Trying to figure out the healthiest way to eat keeps getting more baffling. Recent news stories question the conventional wisdom that all fat is bad for you. Meanwhile, the old guidepost — the U.S. Department of Agriculture's food pyramid — has come under increasing fire.
Walter Willett, chairman of the nutrition department at the Harvard School of Public Health, wants to throw out the USDA guidelines entirely and replace them with a science-based Healthy Eating Pyramid. A new study of 100,000 people shows that switching to Willett's dietary scheme — which emphasizes whole-grain foods, plant oils, and plenty of exercise — cuts the risk of cardiovascular disease in men by 39 percent and in women by 28 percent.
Willett, who put himself through college by selling home-grown vegetables, discusses the latest findings on nutrition with associate editor Josie Glausiusz.
Discover: Why do you want to throw out the USDA food pyramid?
Willett: At best, it's a lost opportunity to help people make important changes in their diet. At worst, some people are likely to die from following the USDA pyramid because they will be eliminating from their diet healthy fats, such as liquid vegetable oils, that actually reduce the risk of heart disease. The unhealthy fats are the animal fats, mainly from red meat and butter, which are high in saturated fats; even worse are the trans-fats from partially hydrogenated vegetable oils found in some margarines and deep-fried fast foods.
What does your Healthy Eating Pyramid look like?
At the base, we put regular physical activity and weight control. The next layer up emphasizes whole-grain, high-fiber healthy carbohydrates and healthy fats such as liquid vegetable oils and foods made from avocados and nuts. I also encourage eating an abundance of fruits and vegetables. Nuts and legumes are good sources of protein for vegetarians, but adding in fish and moderate amounts of poultry and eggs can also be perfectly healthy.
How does it differ from the USDA guidelines?
We put red meat and butter at the top of the pyramid as things to eat sparingly. Red meat is high in saturated fat, and is related to increased risks of colon and prostate cancer, as well as diabetes. The really big difference, though, is the refined starches and sugars — white rice, white bread, white pasta — which are the base of the USDA pyramid. Those things really are empty calories and have adverse effects on blood cholesterol, and we see a relationship to the risk of heart disease and diabetes. In our pyramid, those are things to be eaten sparingly.
Why are these carbohydrates bad?
First, they don't provide much in the way of nutrients. Second, refined carbohydrates tend to cause rapid, high spikes of blood glucose. The body doesn't like high amounts of glucose in the blood, so it pumps out a lot of insulin from the pancreas, and that brings the glucose crashing down. As a result, two or three hours later you often feel hungry. That tends to increase the frequency of snacking, which probably makes it harder to control weight in the long run. We also have evidence that it will increase the risk of Type II diabetes and heart disease.
How can eating healthy fats like olive oil improve your health?
In several ways. First of all, they help bring down the bad cholesterol and keep the good cholesterol — the HDL — high. And some of these polyunsaturated fats help to reduce or keep the blood from clotting by reducing the blood platelets' tendency to come together. They can also help prevent heart-rhythm disturbances that can lead to ventricular fibrillation, which in turn can lead to dying suddenly.
People are incessantly showered with diet advice. Why should anyone follow yours?
There is a very broad base of scientific evidence to support the Healthy Eating Pyramid, and that's important, because it shouldn't rest on any one study. We have both carefully controlled feeding studies and large epidemiological studies following many tens of thousands of people for many years that show that the type of fat, not the total amount of fat, is what's important for having a good balance of the types of cholesterol in the blood.
If the USDA food pyramid is so wrong, how did it come about?
The Department of Agriculture's first constituency is agribusiness: Big Beef, Big Milk, Big Sugar, Big Grain. Yes, the department has some interest in nutrition, but it's going to be extremely difficult for them to say, "Eat less red meat." The low-fat emphasis is also convenient. The meat people, the dairy people, the baking people, the grain people can all say, "We've got a low-fat version, and this is supported by the pyramid," which it is.
High-fat, low-carb diets are all the rage right now. Do they stand up to scientific scrutiny?
They seem to work better for controlling weight than the opposite, low-fat, high-carbohydrate diet. If you're going to be eating a high amount of fat, however, it's doubly important to make that healthy fat. I don't think this idea of eating all the red meat and cheese you want is a good diet. On the other hand, if you do go on a very-low-carbohydrate diet, it's okay if you emphasize things like nuts and fish and some legumes, like soy.
Does anyone know what the long-term effects of a high-fat, low-carb diet might be?
We don't have good long-term studies. However, there is one group, the Greenland Eskimos, that has had a very low carbohydrate intake, and they seemed to do all right from that, although their general health is not wonderful, mainly because of a lot of tuberculosis. Interestingly, carbohydrates are not an essential part of the human diet. We need glucose to fuel the brain, but we can generate enough, in small amounts, from protein and fat in the diet.
Why eat whole grains, then? What are the benefits?
Most incontrovertible is that they reduce constipation. But we also see lower risks of diabetes and heart disease with some whole-grain/high-fiber products in the diet. There are also some other micronutrients that come along in the whole-grain products — magnesium, chromium — that are stripped away in the refining process along with the fiber. I think for most people the optimal diet is not going to be either the very-low-fat or the very-low-carbohydrate diet, but something in between, which is more like the Mediterranean diet.
Almost one-quarter of Americans are obese. Why?
We've created the great American feedlot. Farmers have known for thousands of years that if you want to fatten up an animal, you put it in a pen so it can't run around and you feed it lots of grains. People are not too different. The vast majority get far too little physical activity. The average number of television hours we watch per week is about 30, and people say they don't have time to exercise, which I find completely incredible. We have a huge abundance of cheap food and a food industry that spends huge amounts of money doing every trick they can, trying to penetrate every human frailty, to get us to eat more of it.
Is there any hope of reducing the obesity epidemic?
It's certainly possible, if there is enough of a commitment to do it. But it will mean that almost every sector of society has got to get involved. The design of buildings and cities to make walking and bicycling more friendly has to be better supported. It also has to involve schools, health-care providers, and parents. If kids are allowed to watch 30 hours of television a week, it's just egregious.
You recommend taking a daily multivitamin. If one is eating a healthy diet, why is it necessary?
Some people may not need it, but there are a few nutrients that are marginal in many people's diets, even if they are very health conscious. One is folic acid. You've got to eat almost perfectly every meal to get the 400 micrograms of folic acid, which seems to be the minimal optimal amount. Vitamins B6 and B12 are short in many people's diets as well. In a mainstream diet, red meat and animal products are actually the major source of vitamins B6 and B12, so if people cut them out, they don't always eat enough legumes to get an adequate amount. Then many people, particularly in the northern half of the United States, are short on vitamin D, because we don't convert enough of it from sunlight when the sun is too low on the horizon in the winter.
What's a typical day's meals for you?
I usually have Kashi breakfast cereal. It's seven whole grains, and you cook it for 45 minutes, and then I usually add some nuts and some fruit that's in season or dried fruit in the winter. Sometimes I take a lunch with some Kashi and add nuts and salad to it. Or sometimes at school they have a stir-fry bar or a salad bar, so I'll use one of those. And for dinner, I usually have some salad, sometimes a bit of chicken or fish.
What's really important to know is that eating healthily is not a punishment, that it can be even more interesting, varied, and flavorful than the sort of mashed potatoes, meat, and gravy diet that I grew up with. There are all these grains — quinoa, barley, rice, wheatberries — that can give the diet a lot more variety, flavor, and texture compared to mashed potatoes. There are different kinds of vegetables and ways of preparing them and a variety of cooking oils and nuts that can give tremendous variety to food.
A group of teens recently sued McDonald's for failing to provide information on the health risks of burgers and fries. What's your opinion of the case?
I think there is some justification for it. Even if they don't win, the threat of lawsuits will have a good impact on the fast-food industry because suddenly they seem to be more interested in making their products healthy. You would like to think that food producers would try to make their products as healthy as they can. But it doesn't happen. To some extent, it's no big surprise, because if you look at the major food brands in the United States, many of them are owned by the tobacco industry. RJR-Nabisco is primarily a tobacco company. Philip Morris owns Kraft. There's this huge web of Big Tobacco and Big Food.
Isn't this a matter of personal decision making? It's no secret that eating hamburgers is bad for you.
You might make that case for adults. But children are really not in a position to make informed choices about long-term health consequences. That's why we don't allow them to buy cigarettes or drive cars or drink alcohol or have firearms. Yet the food industry exploits children who really need protection. They use TV advertising to promote their products to children without any limitation or concern, when it's clearly junk for the most part.