MS. DIANE REHMThanks for joining us, I'm Diane Rehm. Most of us know, if we consume more calories than we burn, we'll gain weight, but the findings of a new study indicate staying lean over time is more complicated. I'll talk with a panel of nutrition experts about specific foods and their effects of weight.

MS. DIANE REHMJoining me here in the studio, Dr. Lawrence Cheskin of Johns Hopkins University and Amelia Baker of Georgetown University. Joining us by phone from New Hampshire, Dr. Walter Willett of Harvard University. And I know this is a subject that concerns each and every one of us, perhaps not all the time, but at certain times in our lives. And this new study has some fascinating findings, so do join us, 800-433-8850, send us your e-mail to drshow@wamu.org, feel free to join us on Facebook or Twitter. And good morning to all of you.

DR. LAWRENCE CHESKINGood morning.

MS. AMELIA BAKERGood morning.

DR. WALTER WILLETTMorning.

REHMDr. Willett, let me start with you. Tell us about this Harvard project that examined food choice and weight gain. What did you learn?

WILLETTThis was actually an analysis of three separate studies, but we combined them all in one and it involved over 100,000 people followed for up to 20 years, so it was a lot of information. And we looked at many different aspects of our diet, many foods and how they related to long-term change in weight and what we found was that many different foods made it either more difficult or less difficult to control our weight over the long run.

WILLETTThe effect of any one food seemed to be fairly small, but if we added them all up, loading our diet up with the foods that help us maintain the weight and minimizing those that contribute to weight gain, it made a really big difference and especially if we combined it with regularly exercising and not watching too much television.

REHMSo were there specific foods, other than potatoes and potato chips, that got a really, really bad rap?

WILLETTYes. The findings on potatoes sort of added up to eat a potato, sit like a potato and look like a potato, but that wasn't the only finding. There was no single food that -- again, that explained a large part. Clearly, as we've seen in other studies, sugary beverages were very a very important contributor to weight gain, especially because people consume them so often, but also, red meat contributed to weight gain and there were some other foods that were related to less weight gain, fruits, vegetables, whole grains and nuts, in particular.

WILLETTAnd one other food we didn't expect to see, but it showed up in all three studies, was that regular consumption of yogurt seemed to be related to less weight gain and that's pretty interesting and certainly needs some follow up.

REHMYou know, the other thought I'd like to follow up on is nuts because I think of nuts as, you know, having a pretty high caloric content. Are you talking about certain kinds of nuts?

WILLETTNo, this seemed to apply to nuts in general, whether they be peanuts or tree nuts and many other short-term studies have found that nuts produce more satiety than many other foods. In other words, a few hours after eating them, we'll be less hungry after having a serving of nuts than potatoes or soda or many other foods and that production of satiety seems to be very important in helping us control our calories.

WILLETTAnd I think that's really what this is mostly about, that if we're satisfied and less hungry a few hours after a meal, we're not so likely to go our snacking, we're not going to eat so much the next meal. And different foods pretty clearly do contribute differently to our long-term (word?).

REHMOf course, the other question is there are different rates of feeling well-feed or quite full. Individual people feel differently and would feel fuller than perhaps other people.

WILLETTYes. There's clearly quite a range of response to any aspect of diet and that's something that shows up in study after study that put people on the same diet and the responses are very different. We don't really fully understand that, so in some sense, we do need to be sensitive to what works for us and what doesn't work for us as individuals.

REHMDr. Walter Willett, he's chair of the Department of Nutrition at the Harvard School of Public Health, he's professor medicine at Harvard Medical School and co-author of "Eat, Drink and Be Healthy." Do join us, 800-433-8850, send us your e-mail to drshow@wamu.org. Dr. Cheskin, I know you have some issues with the Harvard findings. Talk about what you may question.

CHESKINWell, I don't have issues with the study conduct and it's certainly clear what was done and was do with all good intentions of detecting which factors were associated with more or less weight gain in the population, but, as I'm sure Dr. Willett can describe more fully, most studies have limitations and to explain the limitations of this one that I see, is that it is an association.

CHESKINIt's what we call an epidemiologic kind of study and that it's very fraught with danger, especially when it hits the press and people start hearing, oh, maybe I should eat more nuts or maybe I should, you know, stay away from all carbs, you know, because of what was found in the study and, you know, the fact is that it is very variable between people and this is just an agglomeration in a very specific population and this is looking only at health professionals who were not obese to start with, so it's not always clear that you can generalize from that kind of population to everyone else.

REHMDr. Lawrence Cheskin, he's director of the Johns Hopkins Weight Management Center and he is a faculty member in the Department of Health, Behavior and Society at the Johns Hopkins Bloomberg School of Public Health. Amelia Baker, as a registered and licensed dietitian at Georgetown University, how do you see this study and its findings?

BAKERI think that it's a good study in the amount of people that participated in the study and also that it took place over 24 years. That's a long amount of time...

REHMYou bet.

BAKER...to follow a group of people, so this can provide us with a lot of good information. One thing that I thought was very important was that with the increase of vegetables and whole grains and fruit, we found a decrease in potato consumption and in the foods associated with weight gain. And I think that that's interesting. So then eating more of the good foods means that we eat less of the "bad foods." There's no good or bad food, there's levels of good and better in quality of diet.

REHMWell, it sounds as though, at least from what Dr. Willett says, that eating potatoes, white potatoes, over a long period of time is going to put at least a pound or two on you from time to time.

BAKERThe amount of calories that we eat, calories in versus calories out, how much we need versus how much we receive per day, is what determines weight loss or weight gain. So something about eating more potato chips or eating more potatoes is associated with this weight gain, so maybe it's that we're overeating potatoes and eating more calories in potatoes and not feeling that satiety from the potatoes.

REHMWhat about that, Dr. Willett? How do you respond?

WILLETTWell, I think that's right, that it -- there are short-term studies and I quite agree with Dr. Cheskin, that no study is perfect and we shouldn't look at these findings in isolation, but what is important is that what we saw was in general very consistent with short-term studies that looked at responses after even a single meal or responses over a few weeks. Those studies are very important, but again, they have limitations because it's really long-term weight control that's important, not what happens over a day or a few weeks.

WILLETTBut where we can really have more confidence is where there is consistency between the short-term studies and then the very long-term studies. It really wouldn't be possible to do randomized trials that went on for four or 20 years with individual foods and expect people to stay on those for that long period of time. When it's been tried, those studies just don't work very well, so -- but the findings, almost all of them are consistent with what we've seen in the short-term studies and in particular for potatoes, it is very clear that those kinds of carbohydrates that are very rapidly absorbed do make it harder to control our weight in the long run.

WILLETTIt's not an issue of carbs or not carbs. We did find that whole grains, high fiber whole grains, were related to lower weight gain and so it does seem it's a quality of the carbohydrates that much more important.

REHMInteresting. What about did you see any difference between white potatoes and sweet potatoes?

WILLETTYeah, we don't really have enough consumption of sweet potatoes in this study to look at them and we weren't able to answer that question. I think it's an interesting one. There are some more micronutrients in sweet potatoes, but my guess is if you ate them in the same quantities, they might not be too different from regular potatoes in terms of their effect on weight control.

REHMDr. Walter Willett, he's chairman of the Department of Nutrition at the Harvard School of Public Health. Your calls, your comments when we come back. Stay with us.

REHMAnd welcome back. We're talking about a new study that's come out of Harvard regarding the different kinds of food that provide not only calories, but do, in fact, according to this study, put more weight on us than other foods. For example, potatoes, white potatoes, are at the top of the list putting on not only calories, but weight gain over a long period of time. Whereas nuts, which also have a high caloric count, tend to put less weight on us. Yogurt seems to play a rather interesting role as well.

REHMHere in the studio, Amelia Baker, she's a registered and licensed dietician at Georgetown University's Lombardi Comprehensive Cancer Center. Dr. Lawrence Cheskin is director of the Johns Hopkins Weight Management Center. On the line with us from New Hampshire is Dr. Walter Willett, chairman of the Department of Nutrition at the Harvard School of Public Health, co-author of "Eat, Drink and Be Healthy."

REHMDuring the break, we were talking about satiety, Dr. Cheskin. I'd be interested in your thoughts about the roles satiety plays in not only how much we eat, but how much weight we might gain.

CHESKINSatiety's a very interesting phenomenon and it's certainly one that there's a lot of effort being put into altering satiety. Think of a company is trying to come out with medicines that will curb our appetite and yet I've seen a lot of patients who want to lose weight. If you ask a room full of people who are struggling with their weight, when's the last time you were physically hungry? You may get a blank look because we don't let ourselves get very physically hungry, so satiety is not necessarily the major driver of our eating behaviors a lot of it is habit, a lot of it is which habits travel together.

CHESKINAnd one of the concerns I have when we try to isolate very specific ingredients is that we don't really understand what goes along with that. So if you, for instance, look at people who eat, you know, yogurt or who eat Greek yogurt or something, you may find that you've got a high socioeconomic status group who's educated, who's heard that this is good for their GI tracts and so that it's perhaps not the yogurt so much or not the nuts so much, but the people who are eating these foods are more health conscious and more likely to be exercising, just educated and watching what they eat in other ways.

CHESKINAnd it is extremely difficult, even when you ostensibly or what the statisticians call controlling for or adjusting for other factors. There are lots of unmeasured factors like motivation and behavior. So satiety is -- has some relevance. Obviously, you can get filled up on a huge salad with no salad dressing and get 20 calories out of it and that clearly is more filling than one bite of potato or nuts, so it has some relevance, but very often not as much as you'd think.

REHMDr. Willett, what are your comments?

WILLETTWell, I think that's true, that satiety's only one factor, and clearly, the food industry is -- does a huge amount of research on ways to get us -- to seduce us to eat more of their product and they often make them salty, sweeter, package them well and put them in front of us 24 hours a day and most people have a hard time resisting that. We're not -- we're really designed and they've done a huge amount of research to find what makes us eat their product, so those kinds of factors also are very clearly important.

WILLETTAnd satiety -- but satiety does play a role, clearly. We -- the fact that we don't gain more weight is a strong indication of how much feedback there is. If we just had no inhibition, no feedback mechanism that reduces our intake, we'd gain a lot more. And what -- I think one point that I wanted to make here is that we're not talking about the kind of people Dr. Cheskin is referring to. People are already obese that he's working with. We're talking about specifically that -- and that's why this study was somewhat different than others, people who are not obese.

WILLETTBut the problem is that on average, we put on almost a pound a year in the United States. And so after 20 or 30 years, we -- most people -- the majority of people do become overweight and obese and that -- that's what we're really looking at here. And it -- the studies that have been done shorter term do find that the mix of foods that we eat can make a difference and does make a difference in our ability to avoid weight gain overtime.

REHMAll right. And let me just ask you this because we've had a number of inquiries. Who paid for the Harvard study? Who were the professors or people conducting their studies and might there have been links to the dairy, yogurt and nut industries? Dr. Willett.

WILLETTSure. Your caller paid for this study, along with all the other Americans who pay taxes. This is entirely supported by the National Institutes of Health.

REHMOkay.

WILLETTThank you.

REHMI'm glad to know that and to have that clarified. One more clarification, some people think we're talking about potato chips and French fries only. Actually, you've found, Dr. Willett, it was baked, boiled potatoes, too, causing these kinds of weight gain. Is that so?

WILLETTThat's so, but there was a greater weight gain with potato chips and French fries. Clearly, those are designed to be even more seductive and the added fat does add some additional calories there as well.

REHMAnd someone else has asked, "I've heard that artificial sweeteners can cause weight gains because they trick the insulin system." Amelia, any comment there?

BAKERThe newer research is showing that those manufactured sugars, the body's having relatively the same amount of reaction calorie per calorie as for with refined sugars. So in terms of satiety, I can comment on that in terms of an everyday American's diet. It takes 21 minutes to feel full, to feel the satiety. It actually takes a little bit of time for your body to make that message to itself, I feel full now.

BAKERSo when you look at packaging and when you look at what we're serving in schools or when you look at what we're serving at restaurants, portion sizes, it takes not -- it doesn't take too much time to eat a lot of food, possibly overeat your food, without feeling full. When we look at sugary drinks, when we look at soda and the portion size of a soda, 16 ounces, that's usually two servings, not one, and 180 calories per serving, so that's a lot of calories...

REHMIt certainly is.

BAKER...per soda. And to drink a soda wouldn't take 21 minutes.

REHMYeah.

BAKERSo if you have a soda in front of you, there's no cue to stop eating until that soda's done.

REHMAnd we've had several comments like this. "Potato chips and potatoes are two different things. While I do believe potato chips are one of the biggest contributors to Americans' weight gain, plain potatoes are probably harmless. It's the salt and oil in the chips which makes you want them more. Dr. Willett.

WILLETTWell, I think that's part of the explanation, but as you mentioned earlier, we did see some weight gain still, higher weight gain, with even mashed potatoes or baked potatoes as well and those are foods that in other shorter term studies, those are what we call very high-glycemic foods. That starch in the potato is very rapidly broken down into glucose or -- and we absorb it and we see it as blood sugar. And there's lots of studies now that show that that very rapid increase and then rapid fall in blood glucose makes it harder to control caloric intake in the long run.

WILLETTSo it's not a powerful factor, but I think what we're looking at here is small nudges in the direction of weight gain over many years can add up to a few extra pounds. And then, when you look at many different foods doing that, the results is what we see is that pound a year weight gain which leads to an enormous problem by midlife.

REHMDr. Cheskin.

CHESKINI think that's basically correct. I would point out, though, that we have to be very cautious again in interpreting these very specific data. Because the generalized view that people might take in hearing this sort of thing is avoid starches entirely, which, you know, might have value, but might not. I sometimes point to the example of there are a billion people in China who live on nothing but -- or very little other than rice, which is in exactly the same category as potatoes. I don't know if the study found that rice had the same effect. It may not have, but there's no biochemical reason to categorize white rice any differently than white potatoes. And you know, although in China there is a growing weight problem...

REHMYes, yes.

CHESKIN...it's not because of the rice that they've eaten traditionally, it's when they eat fast foods and are less physically active, et cetera. So again, we often don't understand what -- whether it is truly this specific food ingredient that is driving an association, because it's not necessarily causative. And it's only by doing intervention studies and seeing that if you alter these things whether there's an effect. So my greatest fear is that people will read far too much into these kinds of data in a specific population that seem to isolate specific foods...

REHMYeah.

CHESKIN...and alter their behavior inappropriately.

REHMDr. Willett, what about the difference between white potatoes and white rice?

WILLETTRight. That -- I agree that those are going to have very similar biological effects and those should be minimized in a diet, both of them. And what we've seen in our data is that whole grains, like brown rice and other high fiber whole grains, actually are related to less weight gain. And also, less risk of diabetes and cardiovascular disease as well, so I have no question given our findings in combination with all of the other short-term intervention studies that have been done that people are going to be better off eating lower glycemic foods with higher fiber in them for many reasons, weight gain being one of them.

REHMAnd of course, we haven't talked about lifestyle, Amelia, which plays a huge role in whether we gain weight over time.

WILLETTYes, that's very true. And there's some interaction there because I think my grandfather survived the Great Depression eating potatoes for most of his calories, but he was a farmer in Michigan and very active 10, 12 hours a day, so he could eat those kinds of starches like potatoes. But not very many Americans are that active anymore and we do see in lots of studies that our metabolic response depends a lot on our underlying degree of insulin resistance, which is largely a function of how active we are.

WILLETTSo different populations at times in the United States, at times the Chinese, who were very active and are slowing down and watching much more television anymore, the same diet can have quite a different effect, so it is all this -- all of these factors are influencing what we do. And if you only act on one of them, the impact will be quite modest.

WILLETTBut what we saw here is when you put together a combination of good foods -- there are good foods, there are bad foods, you minimize the bad foods -- and be active, not watch much television and that is associated with much less weight gain over the long run. I quite agree, there's no single isolated food and that's one of the messages that our study shows...

REHMAll right.

WILLETT..that there's no single solution, it is this whole package.

REHMDr. Walter Willett of Harvard University and you're listening to "The Diane Rehm Show." Amelia, would you like to comment on lifestyle?

BAKERLifestyle is a big part of our entire weight loss and weight gain spectrum. Physical activity is something in Dr. Willett's study that was associated with weight loss over these four-year periods. But what I can tell you from a physiological perspective is that physical activity not only burns calories while you're doing it, but it also raises your BMR, your Basil Metabolic Rate, so after you have stopped exercising, you continue to burn calories at a higher rate. And this is very important to consider over the long run. And people that exercise regularly, how that can positively impact their lifestyle.

BAKERAs we age, our caloric needs decrease, so this is a 24-year study and it's important to note that the physical activity is associated with weight loss. So these people are continuously meeting their caloric needs or undercutting to the point where they're losing weight. So physical activity in reducing -- in heart health, in reducing risk for oncology diagnoses and in risk for obesity is very, very important to consider.

REHMAll right. I'm going to open the phones. We have many callers waiting. First to Boston, Mass. and to Larry. Good morning, you're on the air.

LARRYHello. I'm referring to what Dr. Willett said early in the program, and I've heard this a lot, that nuts are an excellent food, but given that they're pretty high in fat, what kind of serving size is he talking about and are some nuts better than others, based on fat, than others?

REHMDr. Willett.

WILLETTWe didn't see any difference between different kinds of nuts. I don't -- and from a nutritional standpoint, they are very similar, except chestnuts have a lot more carbohydrate. But in general, nuts are pretty similar from nutrient standpoint. And yeah, serving size is important and you can overeat almost any food, including nuts, and that will lead to weight gain.

WILLETTBut here it's more choice -- an issue of choice. If by comparison you're going to have a snack, you are hungry and one choice is potato chips, another choice is nuts. What this is suggesting, and it is again consistent with lots of other short-term intervention studies, that you will be less hungry a few hours later with the nuts rather than the potato chips.

REHMInteresting.

WILLETTAnd again, there's many other good metabolic effects associated with nuts that are related to lower risk of cardiovascular disease as well.

REHMAmelia.

WILLETTIt's that kind of choice that we make pretty often and it does look like that kind of choice can nudge us in a better direction or in a worse direction.

REHMAmelia.

BAKERIn terms of satiety, fiber, fat and protein are big factors in feeling fullness. So like I said before, it takes you 21 minutes to feel that fullness. And the fiber, fat and protein...

REHMSo excuse me, but the more slowly you eat...

BAKERYes.

REHM...and chew...

BAKERYes.

REHM...the more you are going to feel that satiety.

BAKERAbsolutely. And that's why I tell my patients not to distract themselves while they're eating. Have lunch with a friend, but don't watch television while you're eating lunch. You're much more prone to overeat when you're distracted. If you can pay attention to your food, then you can get much more enjoyment out of that and feel satiated. In terms of nuts...

REHMAnd serving size, yeah.

BAKERYes. That's 17 almonds or a small handful or one-quarter cup is a serving size of nuts. So just like those sugary drinks, how it's very, very easy to overeat, you should be portion-sizing those nuts. So instead of having a big bowl, you should have just that quarter cup in front of you.

REHMAmelia Baker and she is with Georgetown University. Short break, right back.

REHMAnd as we talk about the latest Harvard study on nutrition, weight gain, that singled out white potatoes a peculiarly weight gaining vegetable, here's an e-mail from David who's a potato farmer in Washington State. He says he's been involved in several studies on nutritional value on russet potatoes and found repeatedly that people gain more nutrition for your body than weight. Also he says, "I'm wondering if they found on red potatoes and weight gain?" Dr. Willett?

WILLETTWe didn't have data on russet potatoes versus red potatoes, we didn't make that distinction and there may be some subtle differences, but the large majority of potatoes are going to be russet-type potatoes in the United States, so that's in reality mainly what we were looking at. I did want to go back though. I mentioned, again, the press picked up a lot on potatoes and that was perhaps a little bit of an unfair focus on them because that was one of many different factors we saw related to higher weight gain and again soda consumption was -- is the number one problem.

WILLETTPer serving, it wasn't more than potatoes were, but many people have two or three servings a day of soda and not very many people would have that -- very few people would have that many potatoes, so the big picture is sugary beverages and soda. I don't think we should get distracted from that point.

REHMAll right. Let's go back to the phones to Boyds, Md. Good morning, Dale, you're on the air.

DALEGood morning. This subject has interested me for some time and I have been reading research-based opinions that the conventional notions stated so emphatically by the dietician earlier that calories in minus calories out equals weight change is just not true and that this study is just one more piece of evidence that that is not true. I was surprised that she wasn't challenged when she laid down that gauntlet.

REHMAnd what you're saying is that this study, because it points to particular foods, sort of challenges the idea that it's calories in, calories out?

DALEYes. In this study, with a good bit of other research, but since it runs against the establishment, the conventional wisdom of the public health professional, it is -- all such points are usually ignored and refuted as quickly as possible and I was hoping that there would be a discussion on that subject.

REHMAll right. Dr. Cheskin.

CHESKINIt's something that I think is widely discussed and often misunderstood. Yes, in the simplest terms, you can say, nobody defies the laws of thermodynamics, so I can promise you, I sometimes joke to someone who is struggling with their weight, I promise you, if you let me lock you in your room and slide the food under your door, I can make you any weight you want to be. So ultimately, yes, the calories count.

CHESKINThere are some subtle differences in the way we metabolize, there's something called the thermic effect of food, how many -- how much of the calories you waste in digesting, processing, storing, at that sort of thing, which are not necessary, I think, for people to fully understand, but I think it is diluting ourselves to think that if you simply eat certain kinds of foods, that you defy the laws of physics. It's still based on whether the amount of calories you're eating balances how much physical activity you're doing.

REHMOkay. But you were talking earlier, Dr. Cheskin, about vegetables. For example, if you ate a head of broccoli, you would feel full...

CHESKINYes. Very full.

REHM...but you would not gain a great deal of weight.

CHESKINYes, yes. So you can manipulate your satiety and that is a very important thing to do, even though I said earlier satiety is not the whole story by any means, it's valuable.

REHMBut if you ate the equivalent of the bulk of a head of broccoli in terms of nuts, surely you'd gain weight?

CHESKINAbsolutely.

REHMOkay.

CHESKINSo there are also the calories count, but it doesn't track with satiety and fullness very, very well.

REHMOkay. And Dr. Willett, I want to get back to the question of yogurt because it sounds as though even those who were doing the study don't quite understand why you had the findings you came to.

WILLETTYes, and if I just might add, though, that I also agree that our study did not refute the idea that a calorie is a calorie. I think we're mostly talking about foods that make it easier to control our calories from foods that make it less difficult to control our calories.

WILLETTYogurt was, yes, unexpected to us and I think that particular finding because there's not a body of other literature that's looked very specifically at interventions with yogurt in the short-term to see if it affects weight and caloric intake. I think that finding does need to be confirmed with other kinds of research, but there is actually a lot of interest and activity in the probiotics, the lactobacillus that are contained in yogurt and if we consume those kinds of fluids -- foods, it can change the microorganisms that live in our bowels and in animal studies, it does look like that can affect our weight control and weight gain in the longer run.

WILLETTSome of these organisms leap to a higher inflammatory state than others and there are some very plausible reasons why that could make a difference, so I think this a signal that more research needs to be done along both...

REHMNow, what about probiotics in pill form?

WILLETTThere's a lot of interest in that. I don't have very active research. I don't think the answers are in final state yet.

REHMDo you want to comment, Amelia?

BAKERGetting our nutrients from food sources, the body absorbs those micronutrients and macronutrients much more easily. So if you're going to take a pill of vitamin C, it's much easier to get that -- the vitamin C absorbed in your body if you take it with food and it co-absorbs with other vitamins, than if you were to take it by pill.

BAKERThe other thing to recognize when taking supplements is that sometimes while a supplement sits on the shelf, it oxidizes or it decomposes in some ways. So taking these pre and probiotics in the form of yogurt makes sure that they're alive and they're in that yogurt. These are microorganisms and the precursors to microorganisms. Soluble fibers are prebiotics and they feed those probiotics in our small intestine.

REHMAll right. Let's go to Traverse City, Mich. Good morning Kelly.

KELLYHi, this has certainly been an interesting conversation. I just wondered if any of the panel had heard of the book "Potatoes, Not Prozac" by Kathleen DesMaisons? I am calling, I guess, in defense. It's been interesting to see how many people came to the potatoe's defense here.

KELLYShe runs alcohol recovery program and is claiming that the timing of proteins and carbs going into your body can actually change your cravings for alcohol and sweets and she claims over 90 percent success rate with the alcohol recovery, but also, my brother had used this program and lost 30 pounds just by having a plain baked potato every night before he went to bed. Didn't have the cream cheese and butter and all that other stuff on it, but I was wondering if there was any comment to be made on how the potatoes with the specific timing connection would helpful or...

REHMDr. Cheskin?

CHESKINWell, I would just throw in a note of caution and I'm not totally familiar with that work. There are certainly things in foods that can have effects on mood. Amelia and I were just communicating that brain serotonin levels, for instance, when you have carbohydrates, and it can be jelly beans, will raise your feel-good neurochemicals in the brain, one of them being serotonin and the other one being dopamine and this is the one of the reasons people, you know, seek chocolate and other things that make them feel good. But again, the calories themselves, having a potato before you go to bed, it's hard to conceptualize how that is going to cause weight loss.

CHESKINNow, on the other hand, if you talk something up and you say, well, there's all this research on serotonin and it'll make you feel better and it'll curb your appetite, there's a large, you know, bias towards people who want to control their weight anyway, getting a benefit from that sort of thing and it's just our job as the scientists and health professionals to make sure that this passes, you know, the test of scientific credibility.

REHMAmelia?

BAKERAnd this also speaks to the obesity epidemic in America. Obese populations have much higher levels of depression, so this is a kind of a diet that makes sense, that it targets these feel-good hormones in our body, so having a balanced diet will keep your body and your hormones balanced and make you feel good regardless.

REHMDr. Cheskin.

CHESKINThere are so many factors, it is unfortunately a very complicated thing when you look at rates of obesity in the United States. And some of it, you know, raises the question of, is it really specific foods. If you look at socioeconomic status, if you're poor or if you're black, if you're Hispanic, you're far more likely to be obese. Some of this, perhaps, is genetic, perhaps it's environment and we're just starting to understand what the different factors are, but food is just one of those factors.

REHMWell, and of course, we've heard from many sources that socioeconomic conditions do play a role. If you're living in the inner city and there's no good grocery store with green vegetables and other things to help you nutritionally, you're going to go for potatoes, potato chips and dessert. Amelia?

BAKERThere was a great article in The Economist about food deserts last week and these are places in the United States that the USDA has a website that tracks the food deserts and it shows places where people don't have access to fresh fruits and vegetables. Now, the definition of a food desert is changing and has been changed by the United States, but it's very important to recognize who has access to what. And I think that this is very important for the American government to recognize in programs and how we target this problem because lower socioeconomic status is related to obesity. Obesity is also related to food insecurity.

REHMIs obesity necessarily in certain regions around the country, Dr. Cheskin?

CHESKINYes, there is variability and that leads us to again say, is this related to other things besides what we're specifically eating that is driving this? If you say Colorado is the thinnest state, which it seems to be and has been for a long time, is it because there's something very different about Coloradoans and what they eat? Is it that they are...

REHMOr in what they do?

CHESKIN...younger, wealthier and at high altitude and, you know, are more likely to be more physically active, so it is a very complicated picture.

REHMDr. Lawrence Cheskin and you're listening to "The Diane Rehm Show." Let's go to Cynthia, in Hoyt Lake, Mich. Good morning, you're on the air.

CYNTHIAHi, good morning, Diane.

REHMHi.

CYNTHIAYes, this is a fascinating conversation and you've talked about nuts several times, but no distinction has been made between nuts that are cooked in oil, and there are good oils and bad oils, and nuts that are plain. For instance, you can eat plain almonds and I think those are very healthy or roasted almonds, but not roasted in oil or you can eat a handful of nuts that are drenched in oil. So doesn't that make a difference?

REHMAmelia.

BAKERAbsolutely. Most Americans are eating roasted or honey roasted or salted nuts and that makes a big impact on the amount of calories, but the amount of sodium as well.

REHMSo I gather that answers it?

CYNTHIAThank you.

REHMAll right. What about smokers, Dr. Cheskin?

CHESKINSmokers tend to be a bit thinner in the United States than nonsmokers...

REHMAnd doesn't cessation of smoking put on weight?

CHESKINAbsolutely. Yes. And I'd done some studies years ago with whether there was any difference based on what diet you were on 'cause I think often people will substitute food for cigarettes when they quit smoking.

REHMAll right. And let's go to Gary in Gulf Breeze, Fla. Good morning, you're on the air.

GARYGood morning. And I know you don't have very much time.

REHMRight.

GARYI appreciate you doing this. I would like your panel to discuss the difference between a study and a scientific experiment in the sense that a scientific experiment always has a control group. And a lot of studies gather information and they're very scientific about the way they try to do it, but I would like for them to comment on the difference between a study and a control group in a scientific experiment. Thank you.

REHMOkay. Dr. Willett, can you comment?

WILLETTYes, There are different kinds of studies, I think you're quite right. These can all be called studies. There are some where there are randomized groups that one is a control group, one is an intervention group. In others that essentially measure what people do and follow them over time and this study was the latter kind. It was what we call an observational study as opposed to an intervention or randomized control trial.

WILLETTAnd they both, as Dr. Cheskin said earlier, have their advantages and disadvantages. Can't go into all of those, but again, the most reliable kind of information or conclusions will come when we have different kinds of studies showing similar results. And in this case, except for the finding related to yogurt, which hadn't been really looked in intervention trials measuring weight gain over the long run, most of the findings were confirmed by shorter term intervention trials.

REHMAnd quick response, Amelia, on the question of processed foods. How do they contribute to weight gain?

BAKERProcessed foods on a whole have much more calories, ounce per ounce, than foods that we find that are vegetables...

REHMFresh.

BAKER...fresh fruits, fruits and vegetables.

REHMAnd why is that?

BAKERThrough processing, we make foods marketable to people. We make them sweeter, we make them fattier, we make them have better mouth feel. So in the case of something like peanut butter, we process peanut butter, we put it to high temperatures and high pressures to make it better "mouth feel." And that increases the Trans fats in the peanut butter, so that can contribute to all sorts of other issues, including poor outcomes in cardiovascular health.

REHMAmelia Baker of Georgetown University, Dr. Lawrence Cheskin of Johns Hopkins Weight Management Center, Dr. Walter Willett, he's at the Harvard School of Public Health and author of "Eat, Drink and Be Healthy." The mystery continues and I'm sure we'll continue to talk about it. Thanks to all of you and thanks for listening. I'm Diane Rehm.