The Women's Health Research Program of the National Institutes of Health found that low-fat diets do little to improve health. The program also includes studies of women receiving estrogen therapy, which have shown that the risks of postmenopausal hormone replacement therapy outweigh the benefits.
Dr. Thune, who is in charge of epidemiological research at the American Cancer Society, said that this is not a general study. Judging from the scale and investment of this study, it is simply a "Rolls-Royce-level study." Thun thinks the study could be conclusive. Such a large-scale study is usually done only once, on a particular topic, he said.
However, some people disagree with the aforementioned research. For example, Ernish, director of the "Preventive Medicine Research Institute" in Susalido, California, who has long promoted low-fat diets, pointed out that if the fat content in these women's diets is not low enough, it is the vegetables they eat. And not enough fruit, and the study, even at eight years, is still too short for a study diet.
Others argue that diet itself makes a difference, at least in terms of heart disease risk, as in a "Mediterranean diet" that is low in saturated fats (such as butter) but high in oils (such as olive oil). But in the study mentioned above, women who followed a low-fat diet reduced their intake of all types of fat. However, the researchers said that the "Mediterranean diet" has never been studied on such a large scale.
Howard, an epidemiologist who participated in the study, said that everyone should understand that diet alone is not enough to maintain health. "We can't avoid any chronic disease by changing what we eat," he said. "People think it has something to do with what they eat, but they don't notice how much they eat, or whether they smoke or don't exercise."
With the exception of not smoking, much of the advice about healthy living is based on indirect evidence, Howard said. For example, most medical researchers agree that a good diet, weight control and regular exercise can lead to good health.
Some warn against putting too much faith in a particular diet's ability to significantly improve health, and that a person's development of chronic disease is not entirely in their hands. Genes also play a role.
Friedman, a statistician at the University of California, Berkeley, who is experienced in the design and analysis of clinical trials, believes that the above research results should be faced with caution. He said the study itself was well designed, and the investigators intended to confirm some popular hypothesis that a low-fat diet had a protective effect against three major diseases in women, but it turned out that the diet had no effect at all.
This research is confronted with a difficult problem. For decades, many scientists have said that the composition of people's diets determines which chronic diseases they are likely to develop, and most people believe this statement. But this is difficult to prove. For example, research on the relationship between dietary fiber intake and colorectal cancer cannot prove that fiber has a protective effect; and people often believe that vitamins can prevent cancer, and related research has not been able to prove that vitamins have this effect. Many cancer researchers are skeptical of many hypotheses about the relationship between diet and cancer, but the general public still believes in them.
In addition, the study gave researchers the opportunity to test some popular notions about the relationship between diet and obesity. Women on a low-fat diet maintained a stable weight despite no intention of losing weight. It is generally believed that Americans are obese because they consume too much sugar (carbohydrate). Follow a low-fat diet, even if the calories are the same as those on a high-fat diet, but eating too much sugar will lead to weight gain, insulin and blood sugar rise, thereby increasing the risk of diabetes. However, this was not the case in this study.
