The truth on foods and fats
Walter Willett is trudging up a long hill in a hamlet outside of Rome, taking advantage of a trip to Italy to see how olive oil is pressed. A professor of epidemiology at the Harvard School of Public Health, he is passionate about oil or, more precisely, fats. Saturated fats, trans fats, healthy fats like olive oil, and the risk of becoming too fat have played major roles in Willett's research and his vision of how humans can live healthiest and longest.
Most Americans may have never heard of Walter Willett, but they probably have been affected by his research. Aided by a team of scientists at Harvard's Nurses' Health Study, the largest women's health project in the world, Willett has produced many of the major observational studies linking diet and lifestyle to health. "Before Walt came along, we thought nutrition was related to disease--somehow," says Harvard's Frank Speizer, who began the Nurses' Health Study in 1976. "But the actual relationships between nutritional factors and chronic disease--Walt Willett should be credited with putting those on the map."
The list is long: Willett and his team have shown that alcohol increases the risk of breast cancer; that animal fats can lead to heart attacks and aspirin can prevent them; that coffee reduces the chance of diabetes; that daily walking is critical to good health and a long life. Their studies have described how fiber, fish, folate, and fruit may prevent diabetes, coronary disease, cancer, and blindness; how luncheon meats may lead to diabetes and margarine to cardiovascular disease. They've uncovered the costs of obesity; the benefits of olive oil and peanut butter; the hazards of refined starches and TV; the power of vegetables, vitamins, whole grains, and more.
Connections. Willett and his group publish some 50 papers a year in top medical journals--an astonishing output. But these epidemiological studies all show associations and risks rather than specific cause and effect. For that, science relies on testing Willett's associations with randomized clinical trials.
Willett grew up on a Michigan farm, eating red meat and potatoes. Yet, he now advocates a traditional Mediterranean diet of fruits, vegetables, beans, whole grains, fish, and olive oil as a primary source of dietary fat. His bestselling 2001 nutrition book, Eat, Drink, and Be Healthy, supports this diet, while attacking the U.S. Department of Agriculture's food guide pyramid for its low-fat approach.
Willett has never been a scientist who shrinks from controversy. "He upsets a lot of people," says Margo Wootan, director of nutrition policy at the Center for Science in the Public Interest. "He thinks about the implications of his research and advocates changes." The best example: his fight over trans fats in prepared foods.
Small amounts of trans fats occur naturally in some foods. But most result from cooking or baking with liquid vegetable oils that have been "hydrogenated," or formed into solids by the addition of hydrogen (think margarine). Their long shelf life made these oils the fat of choice for food makers and fast-food chains.
Early studies in animals indicated trans fats might lead to heart disease. They increased LDL, the "bad" cholesterol, while depressing "good" HDL cholesterol. In 1993, the Nurses' Health Study found a 50 percent increase in heart disease associated with trans fats in food. A year later, Willett dropped another bomb: People who ate the most trans-fat-rich food were two times as likely to have a heart attack as were people who ate less of these fats.
Joint effort. By the spring of 1994, Willett and CSPI had joined forces to persuade the U.S. Food and Drug Administration to require trans-fat labeling on food products. Willett's 1997 study estimated that use of hydrogenated oils was resulting in 30,000 heart-disease deaths per year, representing "the biggest food processing disaster in U.S. history."
These efforts did not endear Willett to the food industry. Indeed, some companies refused to support conferences if Willett was invited to speak. But by 2002, the evidence was overwhelming: The Institute of Medicine reported that the safe amount of trans fat in the diet is zero. In July 2003, the FDA ruled that trans-fat food labeling must begin by January 2006. But Willett no longer believes labeling is enough. In May, he and 27 other scientists urged the FDA to remove hydrogenated oils from the "generally recognized as safe" list of food additives.
Most recently, Willett has been championing "the glycemic index" as a way of judging which foods may be fueling the epidemics of obesity and diabetes. The GI was developed as a lab tool to rank how quickly carbohydrates raise blood sugar. Willett found an association between eating some foods with a high glyce-mic index--such as potatoes and white rice--and diabetes and heart disease. In theory, foods with a high GI release sugar in-to the blood rapidly but leave people hungry, leading to overeating and weight gain.
The problem with this theory, says Xavier Pi Sunyer, director of the New York Obesity Research Center, is that carbohydrates have not been associated with a high frequency of diabetes. "Asians traditionally ate a high-carbohydrate diet with a high glycemic index--lots of rice, low in protein and fat, and they had low rates of diabetes, heart disease, and obesity," he says. Others agree that the evidence is mixed at best. Says nutritionist James Kenney of the Pritikin Longevity Center: "The No. 1 reason for diabetes is overweight. People who have lost weight and kept it off do not eat a low glycemic index diet--they eat a low-fat diet and exercise a lot."
Whether the GI concept will play a major part in reversing obesity is unclear. But in the end, no one denies that Willett's role in nutritional science is enormous. "I think what we've contributed is the magnitude of the importance of diet and lifestyle to health," he says. One small regret: "I never connected with the olive-oil presser." When Willett arrived, the man was on holiday.
This story appears in the July 12, 2004 print edition of U.S. News & World Report.