PSYC 123: The Psychology, Biology and Politics of Food

Lecture 5

 - Biology, Nutrition and Health III: The Psychology of Taste and Addiction


This lecture addresses the complicated relationship between biology and eating. Professor Brownell explores the physiology of taste and eating. Many parts of the body are affected when people eat food, and many biological factors affect what people choose to eat, how much they eat, and the way they regulate their body weight. The experimental methods used to assess how body weight is affected by genes are also reviewed.

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The Psychology, Biology and Politics of Food

PSYC 123 - Lecture 5 - Biology, Nutrition and Health III: The Psychology of Taste and Addiction

Chapter 1. Taste and Supertaste [00:00:00]

Professor Kelly Brownell: Let’s talk about biology and eating, an incredibly interesting yet complicated topic. By the time we’re done with this class I hope that you, as I am, will be impressed with just how many factors are affecting what people choose to eat, how much they eat, the way they regulate their body weight, intake of certain nutrients, and the like. There are all these interesting, some cases redundant systems that are affecting what people eat. Then we’re going to take the completely opposite attack next week where — in the next class on Monday, we’re going to begin by talking about addiction, which is really a carry over from this, food and addiction, but there’s just not enough time to cram it into this lecture, and then we’re going to move onto culture and how culture affects eating. You could make a strong argument that eating is driven almost entirely by biology, or you could also make the argument that it’s driven almost entirely by culture; but where it gets extremely interesting is where the two intersect and how the two affect one another. We’ll talk about more of the biology today.

Some years ago I was talking to a person who worked for M&M Mars, a big candy company of course, and two of their biggest selling products are Three Musketeers and Snickers candy bars. This individual told me that they’re — that one of them is preferred much more by adults and the other preferred much more by children and there are properties that I’ll ask you about in a minute that distinguish why one is more attractive to children and the other by adults. Let’s try out the clickers today. Which do you think more attractive to the kids: the Three Musketeers — oh you know what I need to do? I’m sorry. I need to boot this up through another program. I apologize. See I was so worried that we had so much to do today that I forgot to boot this up. Okay, this time it should work. Now you’ve had a chance to think about it as well. All right, so let’s see if the technology is correct. What do kids prefer: the Three Musketeers or the Snickers? Go ahead and log in, make sure the green light goes on. Okay so people are still voting it appears. All right, so let’s stop the voting now and see if this — yeah so 49% of you said Three Musketeers, 51% said Snickers, so almost a dead heat there. Well the answer is the kids prefer the Three Musketeers, adults prefer the Snickers, who can guess why that might be? Yes.

Student: [inaudible]

Professor Kelly Brownell: All right, you got the right answer that it’s the peanuts that make the difference. What is it about the peanuts do you think make adults like it and kids not? I mean kids like peanut butter after all. Texture is the answer. The peanuts introduce a texture like a Nestle’s Crunch Bar would have. Kids tend to like uniformity in texture and tend not to like extra things thrown in that confuse them with the texture, whereas, adults do like things that have texture, so as much as the adults may like the taste of the peanuts in that kind of a thing, it’s really the texture that makes them like that particular candy bar. So that’s one little interesting little sensory property of foods that will affect who likes what.

Today we’re going to talk about how biology affects a number of things and these are very interesting questions: how does biology affect taste? Which foods do we prefer or not? We’ve talked about that some extent before. How does it affect mood? People seek out foods when they’re feeling depressed, when they’re feeling anxious, when they’re feeling lonely. It’s different for some people; how is biology affecting that? Then of course, these other things are very important as well. Just to make a brief distinction on the third bullet point about hunger and satiety, you probably know what those terms mean. Hunger is pretty obvious, satiety refers to how full a person feels and when eating shuts off once it starts. We’ll come back and talk about some animal studies that distinguish hunger and satiety, human studies as well.

Today we’re going to talk about taste and I’m going to introduce this concept that was developed by a former Yale researcher named Linda Bartoshuk on supertasting. We’re going to talk about the physiology of eating, or what the animal researchers call feeding. I’m not sure why it’s feeding in animals, and eating in humans, but that’s the way it is. We’ll talk about energy balance in the body and how body weight gets affected, the genetics of these things, and then we’ll end with this discussion of something interesting called taste aversions.

First of all, taste. There’s sort of this basic Biology 101 that — where people get a sense that there are different sensory properties of taste and different parts of the tongue that perceive these tastes. This has been known for years and it’s easy to map out the biology of this kind of thing. This is a pretty simplistic version of it, but there’s some very interesting work that’s taken this to a new level. You can see how taste effects has such a profound effect on people, and what it does to them, and you see it in facial expression. You see somebody eating something sweet, fatty, that they enjoy and you get a look like that. Somebody eats something they don’t like and you get a look that. And so if you just saw this face on the right and you asked people to say, well what do you think is happening with this man? People could say well he saw something disgusting or he tasted something disgusting, and that word disgust is pretty interesting in this context, but it shows up in facial expressions.

Now here’s the concept of supertasting. This researcher Linda Bartoshuk, a terrific scientist, who was here at Yale for many years and then moved to The University of Florida, has looked at the way the tongue and the body perceives tastes of foods. Her desire, one of her scientific desires, is to map out the biology of these things and to understand how taste affects biology and how biology affects taste. She’s really, as I said, a very fine researcher.

Well one of the things that she’s done is work with something called PROP, and PROP is the abbreviation for this compound that you see on the bottom, Propylthiouracil. It got the — which is a variation of something that got discovered in 1931 by a chemist named Fox. He was working with that particular compound that you see in the top bullet point there, and it exploded in his lab. What happened is he found that the associate got some of this in his mouth, tasted it as quite bitter, but he didn’t taste it at all, and he got interested in why would this be this case? Why would the two of them have the same thing in their mouth, but taste it much differently? It wasn’t even so much that one liked it and the other one didn’t; one of them couldn’t even detect it. That got picked up by scientists, including Bartoshuk, who started looking at this and have this used this compound, the PROP, in many, many interesting studies. What they do is they put a little bit of this on a little piece of paper and you put the paper on your tongue and keep it in your mouth for just a short time.

The population breaks down into three groups. There are groups who can’t even detect it at all, they’re called the non-tasters. There are some people who experience it as mildly bitter; those are the medium tasters. And then the supertasters are people who experience it as extremely bitter. The population breaks down about like this: quarter of the people are at the extremes and 50% of people in the middle.

The interesting comparison is between the non-tasters and the supertasters. What Bartoshuk has done is mapped out the tongue physiology on this, and there’s a part of the tongue shown in this little picture here, of where there’s a high density of these things called fungiform papilla. Bartoshuk and others have shown that the ability to detect this particular chemical resides in that part of the tongue. What you do is just put a little dye on the tongue and then you take a picture of it, and you can actually count, once it’s magnified, the number of these fungiform papilla. If you look at the picture, but the comparison of tasters and non-tasters, you get something like this. So at that part of the tongue each of those white dots would represent one of the fungiform papilla. The supertasters — again the ones who detect that chemical as very bitter — look like that, so really quite a difference. You get this interesting sense between 25% of the population looks like that, 25% looks like the top slide and you could see how people — to the extent this is related to food preferences — how the tongue people are born with, and there’s probably related physiology elsewhere in the body to that, how that’s going to affect what people eat.

Now what she — what Linda Bartoshuk has found is that the people who were the supertasters in that 25% group, and to a lesser extent but still true, of that 50% in the middle, the larger group, they perceive an intense burn from things that are considered food irritants and they also perceive the most intense sweetness from sweet foods. Bitter vegetables, like broccoli and cauliflower for example, are experienced as very bitter by that 25% of the population, the supertasters. The non-tasters don’t experience them as bitter or difficult at all. You can imagine how easy it is for the non-tasters to eat those kinds of things and how difficult it is for the supertasters to eat those, and it also has relationships to desire for fat.

The sweetness is interesting too. If Linda were here doing a demonstration, she would have you all put this on your tongue, see which group you happen to fall in, give you a little butterscotch candy, and then have you rate how sweet it is and how pleasant that taste is. She could predict in advance who would experience it as very sweet and very pleasant, depending on whether you were a supertaster or not, with the supertasters experiencing the sweetness as very desirable and very powerful sensory experience. Coupled together is this turn-off to the irritants, the fresh fruits and vegetables, not fruits so much because they’re sweet but to the bitter vegetables, and then a liking for sweet things. Of course this would affect dietary preferences and therefore health.

This is a very interesting phenomenon that she has found. The way she puts it in more generic terms is this: that the supertasters live on — in this neon world of taste where everything is bright and vivid, vivid and bold and potent; whereas the non-tasters live in this pastel world where they’re not experiencing as much preference for sweets nor the aversion to the bitter vegetables and things. And so you would expect from that point of view for the supertasters to have greater problem with weight, greater problems with diet related to health than is the case with the non-tasters.

That begins to give you a sense of what’s involved just with the taste part of the equation.

Chapter 2. Physiology of Eating [00:12:15]

Now let’s talk about the physiology of eating. Now, I’m going to break this down for you. It took me a lot of time to uncouple all the little pieces in this graph, but I’m going to show it to you piece by piece. This is one conceptualization of all the factors that are affecting taste and affecting what people eat. Central to this are central signals those — they would be the brain and the central nervous system and then over here are peripheral signals that happen outside the brain, mainly from the body’s organs.

Let’s break this down and take it piece by piece and show you how it might all fall together. Let’s start with the brain. First of all, the brain and its subsequent physiological reaction is affected by external factors. The fact that you might seek out certain foods to soothe yourself when you’re stressed means that there are external things going on that make certain foods more desirable to you at some times then others, that would be an example. There are other things like what’s going on in the environment, as we used as an example before, you just had a nice meal at a restaurant, you don’t feel like you could eat one more calorie, here comes the dessert cart and all of sudden you’re hungry again; those are external factors that affect the brain and therefore the physiology. There are central signals and peripheral signals, as I mentioned before. Let’s look at the central signals first. There are signals that are going on in the brain, some of which stimulate eating and others inhibit eating, and that’s the hunger and satiety that we mentioned a moment ago. These things affect — directly affect food intake. How much food intake — what people eat and what kind of foods they eat, have a feedback loop to the brain that affects subsequent intake, so you get this loop going on.

From a common sense point of view, if somebody eats a lot of food, then the feedback loop would go to the brain, I’ve had enough it’s time to stop. There are signals — or I haven’t had enough and I need to eat more and these central signals that stimulate or inhibit eating are — fall into that category. There are certain number of chemicals in the body that stimulate eating, certain ones that decrease eating, and I’ll just point out a few of these. You don’t really need to know what these are but I’ll point out just a few as examples. One would be the NPY which stands for Neuropeptide Y, and the 5HT which is something that you will hear more of in the common language as serotonin. It’s very interesting how these two things affect — affect eating, and the SSRI is the selective serotonin reuptake inhibitors are a class of drugs mainly used for depression. Prozac and drugs like that are SSRI drugs. Those drugs, once they were discovered, the laboratory scientists found in the initial animal studies just looking at whether these drugs were safe or not for the health of the animals, found out that the animals lost weight and there was some suppression of appetite. Then scientists said, well boy if you think there’s a market for depression, just think about the market for weight loss. There was some marketing of these drugs for that at one point but they haven’t really worked out that well.

You can see how these things are affecting food intake in feedback loops to the brain. People eat, how much they eat is determined partly by some of these things, what they eat then affects those things, and you get the feedback loop going on. There’s this — what happens between what people eat and then subsequently, what their brain tells them to eat is a very interesting part of the equation and that’s where the — some of the peripheral signals come in. Your body takes in food, it senses that you’ve had nutrients of one sort or another, a series of metabolic processes kick in, and those affect what happens to the brain subsequently.

Here’s some of the things that fall in those, those are the peripheral signals. These are some of the compounds that determine — that are the peripheral signals. We talked about blood glucose last week when we — or on Monday when we talked about the glycemic index. You eat food, your blood sugar goes up, that’s the blood glucose goes up, and that affects the brain. We talked about hunger and there was the spike with the high glycemic index foods, the lower spike with low glycemic index foods; so the glucose that you see over here is one example of that. Insulin is also very involved, as you might imagine, and then hormones that get talked about more in the press, Ghrelin and Leptin are important players here, and then Cortisol which is a stress hormone, is a player as well.

These act through organs. It’s the effect of food on different organ systems in the body that create the release or the suppression of these things. First the liver is involved in the glucose, so food intake will affect the liver that will determine blood glucose levels. You have the gastrointestinal tract involved as well, so of course your small and large intestine in the stomach are involved here, and those will affect these things, especially insulin and Ghrelin. Then you have the adipose tissue. The fat cells are involved because they’re perceiving signals from the incoming food; those affect Leptin. Then you have adrenal glands that affect the Cortisol. Cortisol, a stress hormone, is an interesting player here. One of your teaching fellows, Alli Crum, will be talking about some of the work that she’s doing in a later class and she’s doing some work that involves a number of these things, a very interesting study that looks at the intersection of psychology and perceptions in biology. These things then have signals that would either increase or decrease eating, and they feed back to the brain in that kind of way. So you put all this system together and you get things like this. This is what happens after food is consumed and this — then it goes back to the brain and the brain — then that affects what people eat subsequently.

If you put it all together you have this, what seems like perplexing picture to begin with. It still might be perplexing but the — what I’m hoping that you take away from this is an appreciation for how many parts of the body are affected when people eat food; how the brain is an important player and what people choose to eat in the beginning; and how all these feedback loops are occurring. It’s even more complicated then this, but this is an interesting start at looking at the picture.

Let’s look at some factors that affect short-term food intake. Now long term food intake, how much people are eating overall, is affected by some overlapping but also different factors, but let’s talk about what people eat in the short term, like in a given meal at a given point in time. There are different ways scientists have looked at this and they’ve measured different patterns of what people eat by breaking things down into this way. What factors determine whether a meal gets started? What determines whether you start eating at a given point? When do you become hungry? What triggers some awareness in your mind that you’re ready to eat? That would determine meal initiation or snack initiation, or whatever. The size of the meal of course is an important factor, and there are real differences here between the meal initiation and the meal size, and then the meal termination comes in here as well.

There have been very interesting studies over the years using different drugs with animals to look at what it does to their appetite. Of course the pharmaceutical companies have done thousands and thousands of these studies in hope of finding drugs that will help people with their eating and their weight. When you do studies with animals you find that some drugs affect the initiation of a meal, they affect hunger, so how likely is it for the animal (or a human) to start eating, and that would be the hunger part of it. Some drugs selectively affect that but they don’t affect how much is eaten once the meal starts. What might go up then is the interval between meals or even how many meals are eaten, but what’s during a meal is untouched by these drugs. Then there are a whole other class of drugs that affects satiety. The interval between meals remains untouched; the likelihood of initiating a meal remains untouched; but how much the organism eats once the meal starts is highly affected by the drug.

That leads us to think that when people have problems controlling their eating, there could be some people who have disorders of hunger — or not disorders necessarily because that makes it too clinical; but problems with hunger and other people might have problems with satiety. Think in your own experience, when there are times when you are eating things you don’t think you should eat or you’re eating more then you think you should eat, what’s going on? Is it the hunger? Do you just want to eat all the time or do you want to eat more often? Or are you eating at regular times but you’re just having trouble eating as much as you think you should and you overdo it and there could be combinations of these things. That’s one interesting broad cut at this whole issue. There are things that affect all of these.

For example, hunger, the biological experience of hunger, will affect both meal initiation and meal size. The appetite, which is what a person’s desire is for particular nutrients or particular foods, will affect both of these things as well. Satiety, which is the sense of feeling full, as I mentioned, will affect when a meal terminates, when the next meal will start because that feeling of full will only last so long and then of course that affect — that will affect the meal frequency. Then there’s a concept that I’m going to explain in a minute called sensory specific satiety that will affect meal size and meal termination. When you add all these things up you have this array of arrows going every which way. Again, you can get a sense of how the biology affects actual eating patterns in these — this — this very interesting network of affects and they come together in very interesting ways.

Let me tell you what sensory specific satiety is in a minute, but before we do that, I’m going to have you use your clickers and to get your sense of another issue. Here’s a product called Munchies, let’s put this into a specific context of a food. Frito-Lay, I don’t know how long ago, at least a couple years or more, introduced a line of snack products called Munchies and there was one in particular in this chartreuse bag that was oriented towards kids. Its Munchies Kids Mix, and each of these Munchies products takes a series of things that Frito-Lay may sell anyway and puts them into a combination, into a mix.

Now this one in particular, this Munchies Kids Mix, if you look at the back of the bag here’s what’s put together in this mix. It’s Rold Gold pretzels, it’s Captain Crunch Cereal right under that, it’s Doritos, it’s popcorn, Smart Food Popcorn, it’s Cheetos, the cheese ball things, and then it’s M&M type candies. These are what are going into this particular snack mix. Now, is this snack mix good or not good for kids compared to what they might be eating otherwise, which might just be one of these things put together — put in a bag? I’ll talk to you a little bit about how the Munchies is being marketed, and Frito-Lay has several different messages on the bag that make it look like its going to be a healthier product for kids, and that there’s something, somehow good about this compared to the normal things.

Let’s compare what would happen here, so I’d like you to use your clickers and we’ll — on the next slide — to see whether you think that if you just sat kids down in a whatever kind of a setting, and gave them unlimited amounts of that and unlimited amounts of that, what they would eat more of and why? Let’s see how your intuition works here. There’s something that I mentioned in an earlier class that was kind of a tip off as to the answer here. The question is how many of you believe that people would eat more Munchies, how many of you believe they would eat more Cheetos, or how many believe it would be the same? Vote one, two, or three here. Okay, a few people still voting, more Munchies, more Cheetos, or the same? Okay let’s look at the graph; let’s see what you guys said. Okay, 78% of you said that it was more Munchies, why would that be? Variety that was the tip off, so I’m glad you guys remembered that. It was nice that you were paying attention early that morning.

Variety is one issue and variety connects with this concept of sensory specific satiety that I’d now like to explain. Sensory specific satiety is what happens when an organism eats the same food over and over, and basically what it means is that the palpability or the likeability of certain foods and desire for them will go down more than for foods that are not eaten. Presumably, this is the evolutionary response to the body’s need for a variety of nutrients. If you eat the same thing over and over again, even though you might really like it, you’re only getting certain nutrients, you’re being deprived of others, and hence, the body sends out this signal that hey I’ve had enough of that stuff it’s time to move onto something else. That’s the sensory specific satiety concept and it’s been studied a lot over the years. There’s a researcher at Penn State named Barbara Rolls and I’ll discuss some of her work later on in a different context, but she has done some terrific studies on sensory specific satiety.

The environment thwarts sensory specific satiety doesn’t it? Again, if we look back to when I was a boy, and think about when you guys were kids, the number of food choices available went way up. There’s not only the number of opportunities to eat has gone way up because there’s food as we mentioned before in the gas stations and the drugstores and schools and everywhere else; but the variety of foods has gone up. Each year the food industry introduces several thousand new food products. Some of them fall out of the market but some of them don’t, and as a consequence, the number of options available today in a supermarket or a convenience store is way, way higher then it used to be. You think of things like this: a restaurant like the Cheesecake Factory with an enormous menu, or you go to a diner they have enormous menus. Anyplace you go it’s really — if you go to a restaurant and they had like six choices you’d think you were getting gypped and there was something wrong with this place because they don’t have enough choices. Then of course, you’ve got the variety in places like this, it’s happening around the world where you have many, many choices of things in supermarkets. In fact, one thing that people notice when they come from poor countries to the U.S. of how many choices we have of a given food. So for example, they often find themselves perplexed by the number of cereals, or the number of different kinds of coffee, or how many yogurts there are in a supermarket. And it’s this dizzying array of choices whereas in other countries they have fewer choices and that actually would — you would consider them being helped by that. Do you have a question?

Student: [inaudible]

Professor Kelly Brownell: Okay, that’s a good question. The question is with kids especially does the desire for variety override the other sensory properties that you might get from a high sugar or a high fat food? These things are all working in competition with each other in some way. It seems from the bare reality of the fact that the population is getting heavier, and heavier, and heavier especially kids, that the things like the fat and the sugar are overriding the sensory specific satiety.

Now the sensory specific satiety would probably have a chance to kick in if there were a narrower range of high fat, high sugar choices, because then the kid would get tired of those particular things; but there are so many choices that the sensory specific satiety probably never really has a chance to kick in. You see things like this happening in all parts of the world, so of course the food choices are really dizzying. Now it’s interesting how Frito-Lay marketed this particular product. First, on the package it says eight vitamins — fortified with eight vitamins and minerals — essential ones. Now what do you guys think about that? Is this a reasonable thing for a company to do? Okay why?

Student: [inaudible]

Professor Kelly Brownell: Okay, so one vote would be yes this is okay because vitamins and minerals are good. If kids are going to eat it anyway, why not throw some of them in? Okay what about some other reactions to this? Yes.

Student: [inaudible]

Professor Kelly Brownell: Okay, maybe the body’s not going to use these vitamins anyway so what use are they? Yes.

Student: [inaudible]

Professor Kelly Brownell: Yes, I’ll talk about that in just a minute?

Student: [inaudible]

Professor Kelly Brownell: Yes.

Student: [inaudible]

Professor Kelly Brownell: Okay so the — this comment was that this is probably not good because there is more harm — I’m assuming you mean from eating the high calorie foods, then you get the good from coming from the vitamins and minerals. This is an interesting thing. Now food companies do this a lot. They fortify foods, and there are cases where the fortification is a very good thing. For example, we mentioned before, putting iodine in salt helps prevent certain deficiencies, folic acid and certain things helps birth deficiencies; so there’s some examples of where fortification is a good public health move and there’s general consensus that it’s a good idea. In this case, the vitamins and minerals don’t need to be in there because (a) American children for the most part are not vitamin and mineral deficient, and (b) if you want to deliver more vitamins and minerals to American children this would not be the vehicle you would choose.

Some critics of these kind of practices say that this is just pure, base marketing to make what otherwise is not a very good food seem healthier then it really is, and make it — it gives permission for parents to buy this. It says yes, this is a good thing to buy because it’s going to help your children. That’s what the critics would say. Now over on the right hand side up there you see that there’s more permission giving. It says that kids will love this — sorry this is cut off, but it said, this is something that both kids and mothers can love. It gives mothers permission to buy it and it has all their favorite snacks in one bag; and then down here you see that it’s eight vitamins and minerals again, no Trans fat and it’s endorsed by Dr. Kenneth Cooper.

Cooper is the father of aerobics. He’s a physician who has a large practice in Dallas, a place called the Cooper Center and he was really the — he was a cardiologist, still is a cardiologist, but he invented the concept of aerobics many, many years ago. He’s gotten in on the nutrition field as well. Well, he started working with PepsiCo which is the parent company to Frito-Lay. In fact, we’ll have a terrific person from PepsiCo as one of our guest speakers later in the class and he can talk about this sort of thing. Cooper then gets paid as a consultant, I don’t know how much, but he gets paid as a consultant and then issues his proclamation that this is somehow a healthier food. But if, in fact, kids are eating more of it, and getting more calories, more fat, and more sugar then they would if they were just eating the regular old food, then this does seem like marketing that’s ill-advised. Putting out a product and then marketing it as somehow healthy when kids might eat more of it is a problem.

Okay, well we did a little study on this that we haven’t yet published, but we did a study where we brought kids into the lab, we found out which of these foods they liked the most and then gave them that versus the Munchies and — to see which they would eat more of. You guys were exactly right: they didn’t eat less of the Munchies, they didn’t eat the same, but they ate more. This creates interesting issues with marketing and biology and the whole sensory specific satiety idea.

Now I’d like turn our attention to the effect of things like stress and a related concept on social position, because a study came out recently on this, it was very interesting. There’s been a lot of interest in the influence of stress on eating and stress affects eating, as I mentioned before, in different ways. Let’s just get a show of hands on this, if you’re stressed — now most people when they’re severely stressed like things are really just out of control in life tend to eat less and eating is suppressed. But at more moderate levels of stress, the kind of things that you’d experience are studying for a tough exam, you got relationship issues going on, family things happening or whatever it happens to be — How many of you under those conditions would say you eat more? How many of you would say you eat less? Okay, so an interesting mix within this kind of class.

It’s interesting that the preponderant response here was to eat more. There’s biology that affects that. Well there was a graduate student working with me several years — a number of years ago named Elissa Epel, here’s a picture of Elissa who’s now on the faculty at The University of California San Francisco. She looks like she’s on TV at this point because that’s a picture of her on TV. Anyway, Elissa was a terrific, terrific young scholar working with us and now has become the leading expert in the world on this particular topic.

She got interested in why stress makes some people eat more and some people eat less. Depression does the same thing by the way, and there were a number of interesting reasons why this might occur. What does stress actually do that would affect somebody’s food intake? Well, it could stimulate hunger so people just want to eat more. It could stimulate satiety or suppress satiety, either one depending on whether you eat more or less. If could affect the sensory — how you perceive food, so if you get a certain amount of pleasure from food x, pizza let’s say, or a donut, or ice cream or whatever it happens to be under non-stress conditions, the one hypothesis is that if you’re stressed your physiology changes so you derive more pleasure from those foods. It could be that the foods have a whole different biological effect then what I just mentioned, and that would the ability to calm down this arousal that gets produced in people by feeling bad. When you’re stressed, your body is aroused.

You’ve all heard of the fight or flight thing, your body is aroused, that becomes an unpleasant state for most people, and one hypothesis is you eat the food and it calms that state down. It soothes you down and makes you feel better. Elissa did a variety of studies to test these different hypothesis. We’re not going to talk too much about the results now because there — they would take a long time to discuss, but they’re extremely interesting and she found not only does stress affect biology through some of these mechanisms that we talked about, but also it affects things like what the body does with the nutrients that come in, and when they get stored on the body as body fat where they happen to go. There is — she has research showing that when eating is done under stress conditions and there’s a Cortisol response that’s related to stress — you’ll learn more about that later — that the body is more likely to take that fat and store it in the abdominal region and we’ll come back and mention that again as we did before.

A very interesting study related to this was published just a short time ago using monkeys at a well known research facility in Atlanta called Yerkes. What they wanted — what these researchers wanted to do is look at social position within a group of monkeys, looking at the dominant monkeys in social groups versus the subordinate monkeys. If — those of you who have had any psychology will have heard about this kind of thing. This is not an infrequently used measure of stress, and how social position affects stress and therefore affects whatever outcome you’re interested in, in this case, they were interested in eating. What they found here is that they compared females in this particular study and looked at the dominant versus subordinate ones. Both groups could eat all they wanted whenever they wanted because food was freely available, that’s what the ad lib means. The subordinates ate less, but not a lot less, than the dominant monkeys, and the researchers hypothesized that this might be due to the stress of being subordinate in the social group; but they were more or less maintaining a normal weight and able to function fine.

They then introduced high fat, high calorie foods to these animals, and allowed both groups to eat ad lib: whatever they wanted of the high fat, high calorie foods and something very interesting happened at that point. The dominants ate a bit more of this food but not an awful lot, but the subordinates ate much more, especially at night when they’re not ordinarily eating.

There were — the researcher — and of course gained weight as a consequence and the researchers hypothesized that maybe the calorie dense foods became a way to soothe the stress to calm the arousal and had much more reinforcing value for the subordinate animals because of the stress they were experiencing due to their social position. Very interesting study here; so here you get a different effect of introduction of a high fat diet depending on where the organism is in the social position, another interesting phenomenon that has to do with stress. Here would be a perfect example of how environment affects biology, which in turn, affects eating.

Chapter 3. Body Composition and Energy Balance [00:39:28]

Let’s talk a little bit about body composition. What does the body do with calories and how does body weight get affected by these? Again, you’re going to start to see both culture, which we’ll talk about later, but you talk about things external to the body and things internal to the body having big impacts. Biology is a player certainly in how people regulate their body weight.

The fact is, if we took all of you and put you on exactly the same diet, the precise number of calories, the precise composition of the food, x carbohydrate, x fat, those sort of things and you all exercised exactly the same amount, and we did this under very controlled circumstances there would be large variations and what your body would do with those calories. On a given calorie level, some of you might lose weight and some of you might gain weight, some of you would stay the same, and if you plotted — did a scatter plot of what would happen to your weight under identical conditions, there would be pretty large variability. That’s all the biology that you’re born with.

Your biology determines to a great extent how your body handles calories, how efficiently it stores them, how it burns them off, how it wastes them through body heat, what it does with your basal metabolic rate that I’ll describe in a moment and the like. This has been shown a number of ways. Weight is driven, as you know, by energy balance. It’s calories in and calories out. Calories as we mentioned before are just a measure of energy, the unit of energy. If energy intake is different then the energy expenditure the difference is felt more or less — most often in the body fat stores and that determines whether people lose or gain weight, and as you can imagine, energy balance is affected in the following way: if intake is less then expenditure weight loss occurs, so this is of course where hunger and starvation come in. Weight gain occurs under these conditions and you have stable weight if intake and expenditure line up. Now you have problems with the top two features here in different parts of the world, overnutrition in some parts, undernutrition in others, and it’s the energy balance that’s helping drive the weight itself.

Let’s talk about metabolism for a minute. The word metabolism comes up a lot. There are metabolism diets; people say I have fast metabolism, you have slow metabolism, people use that word a lot. What does it mean? Well metabolism is essentially the term that describes how your body handles energy. When you consume food, metabolic processes occur that then — that are pertaining to the way your body is handling the incoming energy, the incoming nutrients, and all of this is our metabolic processes and metabolism is the end product of that. This would be — this particular chart here shows calories people burn, the energy expenditure part of the energy balance equation. How many calories are you burning just sitting there? If you stand up would you burn more calories? If you walked across the room would you burn more? If you ran a marathon how many would you burn? How many calories is your body burning just by virtue of being alive? These are all parts of the energy balance equation, part of energy expenditure.

Let’s look at the left hand side of this bar and we’re going to see how it all partitions. What this particular bar shows is that this might be typical energy expenditure for an average person, so say 2,000 calories a day. Now by the way, that’s why when you see the dietary recommendations, that the average person eat about 2,000 calories a day. It would be in balance: you’re burning as much as you eat, you’re not going to gain weight. The pieces of this, first BMR, basal metabolic rate. That’s how many calories — how much energy your body is using just to function. So your cells are dividing, your heart is beating, your blood is pumping, there’s some movement that occurs even if you’re not — if you’re being pretty sedentary. It’s just the body’s need to function, is the basal metabolic rate. You can see that of the 2,000 calories, that constitutes a lot of it. Now the sleeping metabolic rate, which is less then the basal metabolic rate, is how much energy you’re burning during sleep. You’d be burning less during sleep because of course you’re not being as active and the body doesn’t need as much energy. This TEF is called the thermic effect of food. When you eat a meal or you eat any food your body takes in the calories and makes use of it, but it requires bodily processes to do that, and those bodily processes require energy for your stomach to work, your intestines to work and the like. That accounts for the little bit of the energy expenditure but not a lot.

The SPA is spontaneous physical activity. You can see from this graph that not an awful lot of the calories that people burn overall are driven by how physically active they are. Now being physically active is terribly important with regulation of the balance of energy. So it’s really important, but as important or even much more important, is the biology people are born with that affects things like their basal metabolic rate. That’s why all of you on exactly the same diet, exactly the same exercise plan would not have the same thing happen to your weights because of the differences in things like basal metabolic rate. Some people are very efficient with their calories, as we mentioned before, they consume calories-a certain amount of calories, the body doesn’t waste them through heat and by unnecessary metabolic processes; they store those calories in the body fat when it becomes more then the body needs. Other people are less efficient with calories, they’re consuming calories but their body is wasting them, if you will. Now wasting the calories through high-level metabolic processes is a good thing in a culture of abundance, but it’s a bad thing if starvation is a factor in one’s life. Then you want to be as efficient with the calories as possible.

Overall, the amount of physical activity people get as a function of overall energy expenditure is not as much as you might think, but important, very important, I don’t want to underplay that, but these other factors are very important as well in determining what people weigh. If we look at energy expenditure components they change depending on whether a person is physically active. We look at the three major things: the thermic effect of food which is a small part, the energy expenditure from physical energy, and then resting energy expenditure which is essentially the basal metabolic rate. For a sedentary person that might burn 1,800 calories a day, the partitioning will look like this, but for somebody who’s more physically active and might burn 400 more calories a day, say by walking four miles, running four miles, or doing other things, the partitioning would look like this and so the expenditure, the orange part of the circles here from physical activity goes up a lot, by 400 calories to be precise, but it also becomes a greater percentage of the overall energy expenditure picture. That’s why being physically active is such a good idea.

We’ll talk about body composition as well. Weight is one index of how healthy people are but also how much body fat they have is important as well, and that varies. You can have people at a given weight who vary a lot in their amount of body fat. It’s the relative amount of fat and lean body tissue, lean body tissue is the combination of muscle, bones and organs, but people usually refer to lean body mass as muscle because that’s the most important thing that you have some control over; and then that compares to body fat, so percent body fat of course would be a person weighs 100 pounds and if 30% of it is fat then their percent body fat is 30%.

There are different ways of measuring body fat. Three of the primary ones are by looking at body fat skin folds, by weighing people under water, and by using a device called the Dexa machine. Here’s what they look like, the Dexa machine on the bottom, the top left is measuring body fat with skin folds, through skin folds, and there is a device called skin fold calipers that you see a researcher there using on a part of the back there where a pinch of body fat is made, the thickness of it is measured with the calipers. That’s done on several places in the body, and then you can use equations to figure out from that, estimate from that how much body fat a person actually has.

The most precise way, the gold standard of measuring this, is to weigh people under water which is what you see in the upper left. A person sits on a chair, is submerged in water for just a very short time, and their body fat can get estimated from that because lean tissue and fat tissue have different densities and that can be determined through calculations. Of course you could imagine how this is difficult to do with large numbers of people and if you have to have the right equipment. The same would be true of the Dexa machine, which provides a pretty good estimate of body fat as well, but then requires lots of money and things like that. Even doing skin fold calipers, which doesn’t require the expensive equipment, it requires time and training, and so if you’re doing a large population study, say with thousands and thousands of people, that becomes a barrier. So you can see why most studies just measure body weight in people, even if they’re just reporting it themselves rather then at measuring body fat.

Then those measures get put into this thing called the body mass index. Let’s talk now about what that is. There’s been the need to develop an approximation of body fat because body fat, percent body fat is a stronger predictor of health then body weight is, because with body weight you get false positives and false negatives as I’ll describe in a moment. You can’t measure body fat all the time because it costs too much, it’s too difficult. So the body mass index was developed. What it is, it’s an equation that takes weight and height and puts them together into a number that is — then becomes a health standard and the number is an estimate of how much body fat people have. It’s not an estimate of percent body fat but it better reflects body fat then if all you know about somebody is their weight.

If you get somebody’s height and their weight, you create the body mass index, which is weight, in this case expressed in kilograms divided by height squared, expressed as meters and then you come away with numbers that usually range from 12, 13 at the very low end up into the 60s or even higher at the very high end. In this particular graphic you see what the classifications are for underweight, normal weight, and overweight with body mass index. Now you guys have probably heard of this concept, you’ve seen charts with it, you may have calculated your own body mass index or — plenty of places you can do that on the web — and you can get a sense therefore about what this means. This is a better measure then just body fat.

Now body fat and body composition are usually alike. But not always. That’s where you get the false positives and false negatives. For example, you can get exception like this football player, for example. If all you knew was his weight you would assume the guy weighs too much, but he’s very heavily muscled so that would be a false positive for obesity, let’s say. You can have cases where weight can be good but body composition is bad, so that would mean somebody is actually normal weight but they’re in bad physical condition, they don’t have much muscle, and they have more fat then would be optimal. Of course you can have the opposite where weight could appear to be bad but body composition is actually good, so that’s why you need something that is an estimate of body fat.

Here was a graph that shows the relationship between body mass index and actual body fat measured by something like underwater weighing. You get a large sample of people, in this particular study, each dot represents a subject in here and you take their body mass index, just by knowing their height and weight and you see how carefully it represents body fat. The women are in the lighter colored, the orange colored squares and the men are in the blue colored ovals. The lines here show that — several things. This is the average for the women, the line that goes right through there; this would be the average for the man that goes through there.

What you see is a pretty nice relationship that, as body mass index increases body fat increases as well, and if this were a perfect predictor, if body mass index were a perfect estimator of body fat you’d see an exactly straight line that would go at an angle right like this, but it would be straight. So these lines are almost straight but there is some curve in them. So it’s not perfect but it’s pretty good. You can see here that women have more body fat then men, that’s a natural thing, and I’ll describe that in a minute; and also there is some variability in these things.

Let’s just take a couple of data points as an example. Let’s see. Let’s look at the squares for women that you see in the circles. Here would be a case of individual subjects in this study who have the same body mass index but have much different body fat. This shows that there’s some error in this, that’s it’s not a perfect measure of body fat, because two women who have body mass index of about 20 which is in the healthy range have as little as about 12% body fat or as much as 40%. This would be examples of somebody who’s weights are about the same at a given height but they’re in different kind of physical condition, so there’s some error there. There’s also error in this direction where you’d have two people with the same amount of body fat, but would have a different body mass index, and they’re quite different from one another.There are different errors in this but for the most part body mass index is about the best predictor we have, short of doing physiological assessment of what body fat really is in people.

A few composition — facts about body composition, as I said, women have — naturally have more body fat then men. That is probably due to the need to preserve energy for pregnancy and lactation, I mentioned that before. Strength training increases muscle mass in the body and that changes body composition even if the amount of fat stays the same. Muscle is more metabolically active then fat. It takes more energy for the body to deal with a pound of muscle then it does with a pound of body fat, so that’s why things like strength training become a very good idea if one’s concerned about body weight regulation. It’s good for lots of different reasons but that would be one of them.

Normal body fat is about 15% to 17% of body weight for men, 20% to 25% body fat for women would be the typical range. As I mentioned before, men and women tend to store weight in different parts of the body, and you have the apple and the pear shape. I also mentioned before, there are exceptions to this rule. When people gain enough weight they tend to gain weight all over the body, but when people begin gaining weight it’s more likely for women to distribute it below the waist, men above the waist. There’s good and bad news for both men and women in this. The good news for the men, is that the weight stored above the waist seems more readily mobilized when people go on a diet. The bad news is that it’s worse for your health to have the weight stored in that part of the body. For the women, the weight stored below the waist seems little — it’s more difficult to mobilize. It’s protected more heavily by the body, it’s defended if you will; but the good news is that it’s not going to create risk for disease as much as the excess weight stored above the waist.

As I mentioned before, the reason that people think this is the case, is that the fat below the waist is a storage depot for energy in preparation for pregnancy, for all the energy needed to sustain a pregnancy, and then to feed the child, breastfeed the child after that. The female is burning tremendous number of calories doing these sort of things as you might imagine; and that is the part of the body where the fat for that purpose has the energy stored. Because the reproduction is so much — is such an important function to defend, the body defends that way in particular compared to the apple shape that might occur above the waist. So a very interesting part of biology of that.

Chapter 4. The Genetics of Body Weight [00:57:20]

Let’s talk about genes and body weight. How much is body weight affected by genes? Well it’s affected a lot by behavior of course-how much one eats. It’s affected a lot by culture, I mean we’ve got rampant things like obesity in the United States, you’ve got almost none of it in a country like Somalia, but then biology is also an important player potentially. I’d like to have you guys do a little vote with your clickers and I’d like you to estimate — now somebody responded already before I’ve described the question but maybe it doesn’t matter. How much of the variation in body weight in a population is explained by genetics? Now that doesn’t mean — so 0 to 25% doesn’t mean that 25% of people who are overweight are overweight because of genetic reasons. What it means is that in a population that either weighs a lot or a little, how much is driven by genetics, and as weight varies within a population how much is driven by genetics. Do you think its zero to 25%, which would mean genetics are having a pretty small contribution; 25% to 40%; 40% to 70%; or 70% to 100%, that would mean genetics is having a very strong contribution to body weight? Okay. Let’s see. Everybody done voting? Let’s see what your graph says. 14% of you said zero to 25%. The majority or more then anything else said 25% to 40%, 40% to 70%, 39% and then a few said 70% to 100%, so most of you are clustered in the middle somewhere.

Well let’s see what the number really is. There are several prominent researchers who have done studies on genetics and body weight, and you’ll hear some of them referred to later in the class, and I’m going to show a video clip today that has one of the figures interviewed. This is Rudy Leibel who is a very well known physician researcher at Columbia University who has studied this. This is Albert Stunkard at The University of Pennsylvania who did the initial human genetic studies on body weight regulation and Claude Bouchard is at a place called The Pennington Institute and he’s one of the world leaders on these as well. II’m going to show you some data from studies that these folks and others have done.

There are different methods for studying the genetic contribution to anything. If you’re interested in how much genes contribute to hair color, to depression, to schizophrenia, to heart disease, to cancer, or to body weight regulation these are the kind of methods that typically get used. First, you can do animal studies where you can actually go in and measure genes, you can do that in humans of course too. Or you can manipulate genes by breeding animals to be a certain way. You’ll see some examples of that. You can do family studies to see how well — how much certain things cluster in families. Let’s just say you look to see whether — if parents are overweight whether they’re more or less likely to have overweight children, and so you can see the clustering in families. Now that’s easy to do from a research point of view but has weaknesses as well, as you can imagine because the families also share culture and environment, not just the biology.

Adoption studies are an interesting issue here as well. That’s when you look at people adopted versus their biological relatives who are not. Identical and fraternal twins, twins reared together and apart, and then of course you can go in and do gene studies. Now I’d like to describe a couple of these.

First, there are ways you can breed obesity and in this case there is a laboratory strain of mice called the OB/OB mouse that’s bred to be obese, so you can look at the genes that are doing this. Here are more examples of that kind of thing. These have been used for years in laboratory studies. I’d like to show you this little video clip, in this case, Rudolph Leibel, the researcher I mentioned is interviewed, but it talks a little bit about this issue, about biology.

[video playing]

Interesting here that he talks about cultural perceptions, that we accept the fact that height is very genetically determined but less so with weight because of the way we’ve been trained to think about this issue. But in fact, biology is an important player.

One of the first studies done with humans on this was done by Stunkard, one of the researchers I mentioned before, in the country of Denmark. Denmark keeps very careful records of adoptees and for research reasons keeps track of people who are adopted later in their life and also the parents who raise them, and the parents who gave birth to them, the biological versus adopted parents. Stunkard, collaborating with Danish researchers, was able to look at these adoptees, people who were adopted at birth; and then as adults, how much they weigh and looked to see whether their weights were closer, more closely resembled those of their biological parents or the parents who raised them. If the relationship was strong between the adoptees’ adult weights and the parents who raised them, it would be a strong argument for culture and environment. If the relationship is stronger with the biological parents, of course then it would argue for genes.

The results look like this. If we look at the right first, the relationship between weights of the children and their mothers and fathers — their adoptive mothers and fathers — as the weights increase here from thin to the median level, to overweight and obese you don’t see a very clear relationship because as the adoptees are getting heavier, the parents aren’t necessarily heavier. So this would suggest that there’s not a very strong relationship between the parents who raised the children and the weights of the adoptees; whereas you get a different picture for the biological parents. As the weights are going up in the adoptees, the weights of the biological parents are higher too, even though there had never been any contact after birth. So this would be a strong argument for biology.

Another very interesting way of looking at this is comparing monozygotic and dizygotic twins: identical twins versus fraternal twins, so of course twins born at the same time to the same parents, raised in the same environment — but the monozygotic twins, the identical twins, share all their genetic material. The dizygotic twins share half of their genetic material. You can look at how the weights of twin pairs relate to each other, how the twins relate to each other in weight. If biology is a player you’d expect a stronger relationship for the monozygotic twins then the dizygotic. In fact that’s what you find. This is a picture showing twin pairs of dizygotic twins, so twins born same time to the same parents, but share half their genetic materials, and each panel here shows one pair of twins, so this would be one pair, another pair, etc.

You can really see pretty striking differences in — some in height but also in the amount of body fat, how — and also other physical characteristics, so you see big differences here, you see big differences here, etc. Then if you look at a picture that shows monozygotic twins who share all their genetic material then what you tend to get are mirror images of one another. It’s another method of estimating the genetic contributions to this issue. So genes are a player to be sure.

I’m going to skip over this and conclude about some of the genetics. Those of you who voted for 25% to 40% were correct. That is the amount of variance in the population that you can explain by genetics. Now the question is, is that a lot or a little? Depends on your perspective. If the culture believes that body weight is completely under personal control, or driven by environmental factors, then hearing this number sounds like a lot; that the biology is really a player and we weren’t expecting it to be that way. On the other hand, this means that less then half of the explanation of population body weight is biological and genetic. There’s at least 60%, and as much as 75% left over to explain — be explained by cultural type factors.

It depends on your perspective, but here are some of the conclusions that people have raised putting genetics and body weight together.

Genetic influences largely determine whether a person can become obese, but it is the environment that determines whether a person does become obese and that extent of that obesity.

Then another similar quote, Genes load the gun and the environment pulls the trigger. So you may have very little obesity in a country like Somalia where starvation and famine become real issues, but if their environment became like ours, then genetics might determine how much weight an individual would gain but the environment would determine whether the whole population is gaining weight. We’ll come back and talk about culture and environment later.

Chapter 5. Taste Aversion [01:07:52]

I’d like to end with a discussion of something on taste aversions because this also is a very interesting phenomenon that has to do with the way our body handles food. How many of you have a strong aversion to at least some food? Okay, most of you said yes. Now my guess is that if we had you write down what those foods are it would highly different from one another because these things tend to get conditioned in by happenstance. You tend to eat a certain food when you’re sick, the body then doesn’t want you to eat that food anymore. There’s a good evolutionary reason for that of course, because in nature if you eat something that makes you sick it means that it’s not good for you, and there’s potentially toxins and poison in that, and so you want to avoid that food as much as possible.

A very interesting example of this was done with coyotes and sheep. In the Western part of the U.S. the sheep farmers are plagued by coyotes eating the sheep and this is — this becomes a real problem for them. So the question is how do you control this process? The farmers and — the sheep farmers and the animal protection people don’t like each other so much, because the farmers want to kill the coyotes and the animal protection people don’t want this to happen. A psychological researcher came up with a very interesting way to deal with this, having to do with food aversions. What they did was they took sheep — like carcasses of dead sheep that the coyotes would ordinarily eat, and laced the carcass with lithium chloride — which when eaten by the coyotes would make them very sick — It wouldn’t kill them but it would make them throw up and be nauseous and feel terrible, and all kinds of stuff like that.

What they found then is the coyotes wouldn’t eat the sheep anymore. The same kind of food aversion that you guys may have experienced got drilled into the coyotes by this particular aversive experience. There are video tapes — I tried to get one but I couldn’t find one — of coyotes coming up to baby lambs and running away whimpering as if that little lamb was going to do something terrible to them because of this aversion, so you can see how strong the biology becomes.

Okay, so we will see you guys on Monday. Don’t forget to turn in your concept sheets outside the room.

[end of transcript]

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