|"Only dull people are brilliant at breakfast"
|"The liberal soul shall be made fat, and he that watereth, shall be watered also himself."
-- Proverbs 11:25
The largest study ever to ask whether a low-fat diet keeps women from getting cancer or heart disease has found that the diet had no effect.
The $415 million federal study involved nearly 49,000 women aged 50 to 79 who were followed for eight years. In the end, those assigned to a low-fat diet had the same rates of breast cancer, colon cancer heart attack and stroke as those who ate whatever they pleased, researchers are reporting today.
"These are three totally negative studies," said Dr. David Freedman, a statistician at the University of California at Berkeley, who is not connected with the study but has written books on clinical trial design and analysis. And, he said, the results should be taken seriously for what they are — a rigorous attempt that failed to confirm a popular hypothesis that a low-fat diet can prevent three major diseases in women.
And the studies were so large and so expensive that they are "the Rolls Royce of studies," said Dr. Michael Thun, who directs epidemiological research for the American Cancer Society. As such, he said, they are likely to be the final word.
"We usually have only one shot at a very large scale trial on a particular issue," Dr. Thun said.
The studies were part of the Women's Health Initiative of the National Institutes of Health, the same program that showed that hormone therapy after menopause can have more risks than benefits. In this case, the diet studies addressed a tricky problem. For decades, many scientists have been saying, and many members of the public have been believing, that what you eat — the composition of the diet — determines how likely you are to get a chronic disease. But it has been hard to prove. Studies of dietary fiber and colon cancer failed to find that fiber was protective. Studies of vitamins thought to protect against cancer failed to show an effect.
Gradually, many cancer researchers began questioning the dietary fat-cancer hypothesis, but it has retained a hold on the public imagination.
"Nothing fascinates the American public so much as the notion that what you eat rather than how much you eat affects your health," said Dr. Peter Libby, a cardiologist and professor at Harvard Medical School.
But the new studies, reported in the Feb. 8 issue of the Journal of the American Medical Association, found that women who were randomly assigned to follow a low-fat diet ate significantly less fat over the next eight years. But they had just as much breast and colon cancer and just as much heart disease.
And, confounding many popular notions about fat in the diet, the different diets did not make much difference in anyone's weight. The common belief that carbohydrates in the diet lead to higher insulin levels, higher blood glucose levels and more diabetes was also not confirmed. There was no such effect among the women eating low-fat diets.
As for heart disease risk factors, the only one affected was LDL cholesterol, which increases heart disease risk. The levels were slightly higher in women eating the higher fat diet, but not enough to make a noticeable difference in their risk of heart disease.
The studies follow a smaller one, reported last year, on low-fat diets for women who had breast cancer. That study hinted that eating less fat might help prevent a recurrence. But the current study, asking if a low-fat diet could protect women from breast cancer in the first place, had findings that fell short of statistical significance, meaning they could have occurred by chance. In essence, there was no solid evidence that a low-fat diet helped in prevention.
"These studies are revolutionary," said Dr. Jules Hirsch, physician in chief emeritus at Rockefeller University, who has spent a lifetime studying the effects of diets on weight and health. "They should put a stop to this era of thinking that we have all the information we need to change the whole national diet and make everybody healthy."
Although all the study participants were women, the colon cancer and heart disease results also should apply to men, said Dr. Jacques Rossouw, the project officer for the Women's Health Initiative. He explained that the observational studies that led to the colon cancer-dietary fat hypothesis included both men and women. As for heart disease, he said, researchers have consistently found that women and men respond in the same way to dietary fat.
The results, the study investigators agreed, do not justify recommending low-fat diets to the public to reduce their heart disease and cancer risk.