Worth noting: early in the interview, Dr. Willet explains that "farmers have known for thousands of years that you can make animals fat by feeding them grains, as long as you don't let them run around too much, and it turns out that applies to humans." Yet at the end of the interview, Dr. Willet states that at the base of the Harvard Food Pyramid (PDF) are exercise and whole grains. They have since updated their recommendations to the plate. It seems difficult to reconcile this advice.
This low-fat dogma was incorporated into the USDA food guide pyramid in 1992?
Well, there's a little bit of complexity. It's interesting. In the '70s and early '80s, while heart disease rates were going bad, we were not talking about low-fat diets. We were talking about replacing saturated fat with a healthy fat, polyunsaturated fat. But somewhere in the mid-1980s, we lost that message. It's perhaps partly because some nutritionists felt it was too complicated to talk about different types of fat, and developed the notion we should just reduce all types of fat across the board. That was really the beginning of the low-fat, high-carbohydrate crusade.
How is the simplification -- eat less fat -- manifest in this food guide pyramid?
Well, the food guide pyramid that was developed in 1991 really is based on the idea that all fat is bad. Therefore [if] fat is bad, and you have to eat something, carbohydrate must be wonderful. So the base of the pyramid is really emphasizing large amounts of starch in the diet. We're told we can eat up to 11 servings a day, and if that wasn't enough starch, the pyramid puts potatoes along with the vegetables, so you can have up to 13 servings a day. That's a huge amount of starch.
Fat's up at the top of the pyramid, and where it says explicitly "fats and oils, use sparingly." It doesn't make any distinction about the type of fat, and it tells us to eat basically as little as possible.
From a public health standpoint, how would you characterize this pyramid?
Well, this pyramid is really not compatible with good scientific evidence, and it was really out of date from the day it was printed in 1991, because we knew, and we've known for 30 or 40 years that the type of fat is very important. That was totally neglected.
[What were the] unintended consequences? The food industry started using vegetable oils, but baking was difficult so they made a technical modification.
In some ways, we do have to credit the food industry with being responsive to what nutritionists were saying. They did believe or accepted the evidence that vegetable fats, vegetable oils, would be better than animal fats, and that really led to the development and promotion of the margarine industry and Crisco, baking fats that were made from vegetable oils. But they were made by a process called partial hydrogenation, which converts a liquid oil, say like soybean oil or corn oil, to something like margarine or vegetable shortening. As it turns out that was a very disastrous mistake, because in the process of partial hydrogenation, a totally new type of fat is formed called trans fat. The evidence has now become very clear that trans fat is far worse than saturated fat.
So when people were told to switch from butter to margarine?
Unfortunately, as a physician back in the 1980s, I was telling people that they should replace butter with margarine because it was cholesterol free, and professional organizations like the American Heart Association were telling us as physicians that we should be promoting this. In reality, there was never any evidence that these margarines, that were high in trans fat, were any better than butter, and as it turned out, they were actually far worse than butter.
People read on the label "cholesterol free."
Right. This is a good example where just focusing too much on one particular piece of the diet, one particular substance or nutrient, can really mislead us. It is true that these vegetable shortenings and margarines were cholesterol-free, and that was pushed. ... Even though these products were cholesterol-free, the trans fats in them raised our blood cholesterol much more than actual cholesterol in the margarines would have done.
"All fat is bad" led to many low-fat products, some of which had beneficial value. Talk about one example.
This campaign to reduce fat in the diet has had some pretty disastrous consequences. ... One of the most unfortunate unintended consequences of the fat-free crusade was the idea that if it wasn't fat, it wouldn't make you fat. I even had colleagues who were telling the public that you can't get fat eating carbohydrates. Actually, farmers have known for thousands of years that you can make animals fat by feeding them grains, as long as you don't let them run around too much, and it turns out that applies to humans [my emphasis]. We can very easily get fat from eating too many carbohydrates, and the public was really directed to only focus on fat calories, when we really have to keep an eye on calories no matter where they're coming from.
With more fat-free products than ever, Americans got fatter.
Right. The reality is that during this campaign for fat-free and reduced-fat products, actual fat consumption did go down, but Americans got much fatter during this period of time. Now of course lots of things were going on at the same period in time, but I think it's highly likely this focus only on fat calories to the neglect of carbohydrate calories has contributed to this epidemic of obesity.
Is it fair to blame the food pyramid when people don't follow it anyway?
The food guide pyramid has actually had a substantial impact on the diets of Americans. If we look back compared to 20 years ago, the percentage of calories from fat in the American diet is quite a bit lower compared to earlier days. Second, there're some important indirect impacts of the food guide pyramid, in that many tens of billions of dollars of federal food policies have to be compliant with the food guide pyramid. So many programs -- for example, what's fed to young children, to pregnant mothers, to low-income families -- have to be consistent with low-fat diets. So the impact really has been, overall, substantial.
Behind the food pyramid were a collection of constituencies. Were people receptive when you raised these criticisms in the '90s?
There was not much receptivity in the 1990s, when we raised these criticisms of the food guide pyramid. It was almost an accepted religious belief that fat was bad and carbohydrates were good. Then there were lots of economic interests behind the food pyramid as well. Clearly the dairy industry is extremely well represented in the food pyramid. The beef industry is there, and it's very convenient that beef is combined along with fish and poultry and nuts and legumes. So each one of those industries can say: It's healthy to have three servings a day of our product.
What makes it so difficult to study the relation between diet and health?
The relation between diet and health is unusually complicated to study, and that's probably why we don't have all the final answers even yet. In a trial of a drug, for example, you can randomly assign people, one group to a placebo and another [group] to the new drug, and see what happens to them. But obviously you can't do that with nutrients or a whole diet very easily.
Second, we have to follow people for many years to learn all the consequences of diet, and perhaps even almost a lifetime, because some of the effects of diet may be operating during childhood and not be manifested until adult life. So there's no one simple kind of study that will give us all the truth about how diet influences our health, and we need to combine the results of many different studies to have the best and most complete picture.
One [kind] of study, for example, involves feeding small groups of people very controlled diets for short periods of time, and seeing what happens, for example, to their blood cholesterol levels. But blood cholesterol levels are only part of the picture, so we are also conducting very large studies where we enroll tens of thousands of people and follow them for many years, all the way along, finding out what they're eating, and then what happens to them in terms of their risk of heart attacks, cancers, and other conditions. And of course in those studies we need to control for many factors, like whether they smoke, how much exercise they have, their family history of various diseases. It's really only when we put those kinds of studies together with the more detailed metabolic, biochemical studies that we can have the best information about the effects of diet.
So you find out what they eat, rule out the bad things they do, and look for associations?
Right. What we do is find out what people eat through very detailed, structured questionnaires, observe what happens to them in terms of disease rates -- heart attacks and cancers, for example -- and then put these together, controlling for other aspects of lifestyle like diet and activity.
What did you notice that seemed to clash with the low-fat dogma?
When we began our studies back in the late 1970s, we expected that we would find a relationship between, say, fat intake and breast cancer, because that was almost an accepted relationship. But as the data started coming in over the years, we just did not find any higher risk of breast cancer among women who consume more fat in the diet. And the same was true for colon cancer and for heart attacks and risk of type 2 diabetes. In fact, the percentage of calories from fat in a diet has not been related to any important health outcome.
Amount of fat has no relationship to coronary heart disease?
The amount of fat had no relationship to risk of coronary heart disease, but the type of fat was extremely important.
So the advice we were getting was not just misleading but dangerous?
Right. The evidence that we accrued really suggested not only that the type of advice that people were getting was not useful, but it actually could be dangerous, because some people were eliminating the very healthy types of fat that actually reduce heart disease rates.
Certain fatty acids can dramatically reduce the incidence of cardiac arrhythmia?
One of the important findings, not just from our studies but several trials conducted by other people in Europe and also some careful animal studies, have very clearly indicated that some types of fatty acids in the diet, in particular the omega-3 fatty acids, can actually reduce the heart arrhythmias that really cause people to drop dead in the street. We call that sudden death. And that's very important because some people were eliminating those critically important fatty acids from their diet because they were told that all fat is bad. ...
Traditionally people think of carbohydrates as made up of simple sugars and complex starches. What's wrong about that?
Right. The thinking in nutrition about carbohydrates really had broken them down into two classes: sugars and so-called complex carbohydrates, which are mostly starches. ... The idea has been pushed that all forms of so-called complex carbohydrates are really the poster child of nutrients, and we should be eating them in large amounts. That's what the pyramid tells us to do. But in fact, these kinds of starches -- white bread, white rice, potatoes -- are starches that are very rapidly converted to glucose, really pure sugar, and almost instantly absorbed into the bloodstream. And these are the kinds of carbohydrates that we really should be minimizing in our diets.
A sugar rush from a potato?
Actually, careful studies have shown, demonstrated that you get a bigger rise in blood sugar after eating potatoes, a baked potato, say, than you do from eating pure table sugar.
That seems pretty extreme. Why is that?
... There are several problems with these rapid rises in blood glucose after you ingest large amounts of a rapidly digested form of carbohydrate. First of all, when the blood sugar goes skyrocketing up, the body wants to bring it back down. So our pancreas pumps out a big blast of insulin, and as a result, the blood sugar comes crashing down rapidly. In fact, in many people, after three and four hours, it overshoots and actually become a little hypoglycemic, and that rapid crashing down of blood glucose and insulin stimulates hunger. That would be no problem, except that it's often all too easy to go in the refrigerator or find a snack, and if we do that frequently throughout the day, that can add up to too many calories over weeks and months and years, and contribute to obesity.
Second, these high rises in blood glucose and insulin have a bad metabolic effect on the blood cholesterol fractions. Specifically the HDL, the good cholesterol, is driven down, and triglycerides, another type of fat in the blood that leads to heart attacks, goes up.
Third, after many years of demand for high amounts of insulin, the pancreas tends to give out. And at that point in time, we've got type 2 diabetes.
[What is the role of insulin?]
The role of insulin is to transport glucose from the blood into the cells, like into muscle or into fat cells.
What can go wrong with this system?
Well, the problem really comes about when we develop insulin resistance. And that means that the cells, like the muscle cells, become more resistant to the action of insulin transporting the glucose inside the cell. And we can become insulin-resistant in several different ways. There's some genetic component, and as it turns our, for example, many Asians tend to have more insulin resistance. Also if we have overweight or low levels of physical activity, we'll be more insulin resistant.
Many people argue the virtues of Asian diets, with a lot of white rice.
Right. The Asian diet as it's traditionally been used raises some very interesting issues in nutrition, in fact, some of the most important findings during the last several years. What we've come to realize is that if we have a higher degree of insulin resistance, then we much less well tolerate a high-carbohydrate diet.
Interestingly, in traditional Asian societies, people were very lean, very active, and therefore had low insulin resistance. They could eat large amounts of rice, even white rice, in the diet and have low heart attack rates and have low rates of type 2 diabetes. But if you take that same person, and they [now] may be living in Beijing and driving a car and watching a television, and they put on a few pounds, they're going to have much more insulin resistance. So if you take that same diet, high in carbohydrate and white rice, they will have a much worse metabolic response and much higher rates of type 2 diabetes.
If you're American and overweight, won't you be put on a low-fat diet?
If you're overweight and living in the United States, and you go to a hospital and see a dietician, almost for sure, you're going to be put on a low-fat, high-carbohydrate diet.
What's your view of that?
The problem is that that's really the wrong diet for an overweight person. Because the person is overweight, in general they're going to have quite a bit more insulin resistance and much less well able to tolerate low-fat, high-carbohydrate diet.
But fats have twice the amount of calories per gram as carbohydrates. Doesn't it make sense to push the low-calorie diet and therefore a diet low in fat?
There's been a very simplistic idea: Just because fats have more calories per ounce than carbohydrates, we should be eliminating fats or reducing fats to control our total caloric intake, in other words, to help control our weight. What's really important though is how satisfying a diet is, because we have very complex mechanisms that control our total intake of calories, and it's become pretty apparent that if we have a high-carbohydrate diet, particularly high refined carbohydrate, it makes it much more difficult to control our total caloric intake. That's probably because when we eat refined carbohydrates, we get these swings in blood glucose and insulin that lead to hunger between meals; whereas if we have a diet that's somewhat higher in fat, we tend to be more satisfied over the long run.
Is this what Dr. Atkins was saying 30 years ago?
Dr. Atkins was saying as much as 30 years ago, that if we reduce our carbohydrate intake to quite low levels, that will make it easier to control our caloric intake and thus promote weight loss. As it turns out, there is a strong element of truth in that. A number of studies in the last year have looked in a very careful way, comparing low-fat, high-carbohydrate diets with reduced-carbohydrate diets, and in general people have done better on the reduced-carbohydrate diets in terms of their weight.
Even though each ounce of fat has twice as many calories, you eat fewer calories because they're more satisfying?
Yeah. Well, first of all, this idea of how many calories per gram of fat versus how many calories per gram of carbohydrate is a little simplistic, because we almost never eat foods that are pure fat and pure carbohydrate. They come in foods as mixes, and often with a lot of fiber and a lot of water, and all of those things make a difference as well. But what is really important in the long run is how satisfying a food will be. And as it turns out, that many high-fat foods -- sometimes like meat, but even think of a handful of nuts -- are often very satisfying even though the physical amount is not very great.
One of the interesting observations in the recent studies that have compared high-fat diets with high-carbohydrate diets is that there are a lot of differences between people; that it's not that everybody loses a certain amount of weight on a reduced carbohydrate diet. Some people lose a lot of weight. Other people hardly lose any, so one of the things we have to come to understand better is the reasons why there's such a difference in response to these diets.
Talk about your food pyramid.
We've tried to put together an alternative food guide pyramid that would be based on the best available science. And of course it is a little bit challenging to boil down a tremendous amount of complex science to a simple graphic, and you really have to focus on the things that are well established and important.
Right at the bottom, we put weight control and regular physical activity, because overweight is the number one nutrition problem in the United States. Almost everyone is going to need to exercise on a regular basis if they want to control their weight over the long run. And this also is a message that all forms of calories are important.
On the next level, we put healthy forms of carbohydrate, meaning whole-grain carbohydrates and healthy forms of fat, meaning from vegetable oils, in the recognition that in most people's diet, most calories are going to be coming from some source of carbohydrate and fat. And what's really important is that those both be healthy sources.
Some of those fats have come right from the top of the other pyramid.
Right. What we've done is, we've brought some of those fats from the top of the pyramid down to the base, because healthy fats are an important part of a healthy diet.
The rest of the pyramid?
Our alternative pyramid, like the USDA pyramid, does emphasize plenty of fruits and vegetables, but we've taken potatoes out of the vegetable group. We've put legumes and nuts as a layer. If you want to be a vegetarian, those are good protein sources. But moderate amounts of poultry, fish, and nuts can also make a diet be a non-vegetarian diet and still very healthy. And up at the top we've put red meat and dairy products, dairy fat, because those are high in saturated fat. ... At the top of the pyramid, we've put foods like white bread, white rice, white pasta, and sweets as those that should be used sparingly. And that was really the base of the USDA pyramid.
Some nutritionists have criticized your pyramid as "floating on a lake of olive oil."
The formal studies that had compared a more moderate fat intake as we've suggested, with low-fat diets, have actually consistently shown that people did as well or better controlling their weight on a moderate-fat diet compared to a high-carbohydrate, low-fat diet.
Even good fats are more fattening than good carbs. So they think you're contributing to the obesity epidemic, or there's a risk of that. A tablespoon of olive oil is 14 grams of fat.
There are all kinds of beliefs about the amount of fat in a diet, tremendously strong opinions. What we really need is sound data, and the studies that have been done show that people actually end up controlling their weight at least as well, and usually better, on moderate-fat diets compared to low-fat, high-carbohydrate diets.
Is it okay to get more than 30 percent of your calories from fat?
The evidence is quite clear that it's perfectly fine to get more than 30 percent of your calories from fat, and probably, in fact, it's even better to be getting more than 30 percent of calories from fat, if it's the healthy form of fat. ...
When you look at the causes of obesity, what do you find?
The causes of obesity and the obesity epidemic in the United States are extremely complex. In fact, obesity is sort of a tip of the iceberg of tremendous social change that's been going on during the last few decades. First of all, our activity patterns have changed greatly. We have children and adults now watching on the average, about four hours of television per day, and in study after study, we've seen just the number of hours of television watching being the strongest predictor of obesity. When I was young and came home after school, we'd all go out and play, and our mothers would have to drag us in for dinner. That doesn't happen very often anymore. Often the mothers are not there. Kids are inside. The television is used as baby sitters. We've also made it dangerous and uninviting to walk to places, to walk to stores, to ride bikes in urban areas, and that's removed an important amount of physical activity from our lives as well.
So the physical activities pattern's changed, but the food environment has also changed. We have food available fast and very low-cost and very convenient, almost everywhere. The food industry has invested many tens of billions of dollars in making their products more attractive, more sweet, more salty, more sexy, more seductive in every way that they can, and we're vulnerable to that promotion, and we are eating more. So you put these two factors together -- reduction in activity, heavy promotion of food -- and you've got, not surprisingly, an epidemic of obesity.
Which we're exporting to the rest of the world.
Unfortunately, what we've created is now being exported to the rest of the world. And in almost every country, in Europe as well as Africa, Latin America and Asia, rates of obesity are climbing rapidly.
When you think about solutions, how can we proceed?
The causes of obesity are very complex, and therefore any response is going to have to be complicated and multi-faceted as well. There is no single solution to this, but we have to do many things to really solve this problem.
We've actually looked at this in a very detailed manner over the past two years in the New England states, and identified eight different areas that we have to really modify. For example, schools have to change what's served, what's promoted in schools. The healthcare providers -- physicians, nurses -- have to be providing much better and effective advice to their patients about controlling their weight. Work sites have to change. The whole food environment and what we promote to children has to be somehow modified, and we do have to protect children from these aggressive advertisements. We have to change the physical environment to make it more conducive, more attractive to bicycle to work, to destinations, not just drive places. Many other things need to be done if we're going to solve this problem, and it's time we really began.
The national obesity crisis, I mean, it's really severe. And to hear you talk about it, it sounds like it's hopeless to overcome it.
The crisis we're facing is severe, and it's getting worse. Interestingly, the full consequences won't be seen for another 30 or 40 years, because it takes that long a time for the risk of diabetes and the complication of diabetes to play out. But it's not hopeless, and I think that's the good news. There are places, if we look around the world, where people have been controlling their weight. For example, in Japan and in Sweden, women have really not been gaining weight as they've gone through midlife and gotten older, so we do need to learn more about how they're doing it.
Also in the U.S. there are many people who are controlling their weight successfully. Not everybody is going to be as successful, even if they do the same diet and do the same amount of physical activity, but many people are doing pretty well. And one piece of evidence we have is that upper-income groups actually only have about half the rate of obesity compared to lower-education groups. So it's not hopeless, but we are going to have to devote many more resources to doing this if, as a whole country, we're going to be successful. ...
The advice for so long was: Buy something that says "fat-free," or at least "low-fat" on it. All these [salad] dressings, fat free. But not necessarily a good idea?
In fact, a pretty bad idea, and that was really unfortunate that the crusade against fat really led the food industry to produce all these fat-free salad dressing products. The problem is that the fats that were in the salad dressings were the healthy fats, the ones you should be including in the diet. They were the unsaturated fats that reduce our blood cholesterol levels, and we've also seen that they reduce heart attack risk and type 2 diabetes, as well. So people were giving up these healthy fats, and what we've seen is actually an increase in risk of heart disease among people avoiding full-fat salad dressings.
Of course one of the important roles of a full-fat salad dressing is that it makes salads taste good, and we want people to be eating those vegetables. So it's not that we're telling people to gulp down bottles of salad dressing. We want them to use it on a salad and enjoy it. ...
[At] the base of your pyramid, after exercise: whole grains. Right?
Right. On the base of our pyramid, side-by-side, we put healthy fats and whole grains. And that's because we do see positive benefits in study after study, that there's lower risks of type 2 diabetes and heart disease, and probably better weight control as well, with some whole grains in the product. And that's because these carbohydrates are generally absorbed more slowly, they give less of a spike in blood glucose, and they come with a whole package of minerals, vitamins, and fiber that all have positive health benefits. ...
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