Eating Lean Doesn’t Cut Risk
Overturning three decades of conventional wisdom, a new study of low-fat diets shows that eating less fat does not significantly reduce the risk of heart disease, stroke, breast cancer or colorectal cancer, researchers report today.
Results on weight loss from the same study, published last month, also show that reducing fats without reducing calories does not lead to significant weight loss.
The $415-million study, which tracked about 50,000 women for as many as 13 years, is by far the largest ever to address the role of fats in health and, though it hints at some potential benefits, largely closes the book on a highly publicized chapter of dietary history.
“Basically, the low-fat, high-starch diets completely struck out,” said Dr. Walter Willett of the Harvard School of Public Health, whose own smaller studies have shown similar results. “This is ... the end of the low-fat era.”
But, he cautioned, “the one really important point here is that it would be a serious mistake to interpret this study as ‘Go and load up on sausage, butter and fast food.’ ”
Experts said that the results on cardiovascular disease and colorectal cancer, obtained in older women, probably applied to men as well because the disease mechanisms are the same. It is not clear, however, if changing the diet earlier in life would produce a different outcome.
The results, published today in three papers in the Journal of the American Medical Assn., might be surprising to a public that has grown accustomed to seeing more than 15,000 low-fat products on the shelves of supermarkets.
But to nutritionists and physicians working in the field over the last decade, they are consistent with new ideas about the roles of so-called good and bad fats.
“Nutrition knowledge has progressed dramatically since the study began,” said Mara Vitolins, a professor of public health sciences at Wake Forest University Baptist Medical Center in Winston-Salem, N.C., and a coauthor of the study. “Today we know that reducing total fat may not be enough -- we need to focus on the types of fat we eat.”
That means reducing consumption of saturated fats like those found in meat and butter and increasing the intake of vegetable and fish oils, which studies have shown have a protective effect.
Although the study found no significant benefits from a low-fat diet, it also found no harm from the accompanying increased consumption of carbohydrates -- grains, starches and sugars.
The finding contradicts the claims of proponents of low-carbohydrate diets, such as the Atkins Diet, that high carbs increase the risk of diabetes.
The women in the study “did not show any signs of diabetes, their triglycerides were normal, and their blood glucose was normal,” said Dr. Elizabeth G. Nabel, director of the National Heart, Lung and Blood Institute, which sponsored the study.
When the study was conceived in the 1980s, fat was perceived as a universal villain.
For weight control, it was a problem because of its high energy density -- 9 calories per gram, compared with 4 calories per gram for carbohydrates.
For cardiovascular disease, animal fats were known to play a role in the buildup of artery-clogging plaque, whereas the role of protective vegetable fats had not yet been recognized.
Studies of women in countries with low-fat diets showed a lower incidence of breast cancer, which rose when the women migrated here and began consuming an American diet. And red meats, which have a high fat content, had been linked to colorectal cancer.
Nabel said the study was initiated to explore these issues, and was conducted in women to broaden the range of clinical trials.
“We realized most clinical trial results came from men, and that we had very little information about health as it related to women.”
The new results indicate that the concerns about fat were overblown.
“People just think fat is the devil incarnate, and that’s an incorrect message,” said Abby Bloch, vice president for programs and research for the Dr. Robert C. Atkins Foundation in New York. Atkins proponents have long argued that fats are harmless.
“Americans unfortunately tend to go to extremes,” Bloch said. “So if you say fat may be bad, then they’ll try to eliminate all fats.”
The trial was conducted as part of the Women’s Health Initiative, a $750-million program that has studied about 161,000 women. Another leg of that study overturned the long-held dogma that estrogen replacement therapy after menopause reduced the risk of heart disease.
For the study, 48,835 healthy women with an average age of 62 were enrolled. Forty percent of them were given intensive counseling -- 16 sessions in the first year and four per year thereafter -- to help them reduce their fat intake, while the remainder continued their normal diet.
The women filled out forms indicating what they ate and were tracked for an average of eight years.
Despite the size and scope of the study, there were problems.
Even with counseling, most women were not able to reduce fat consumption from the average of 35% of their calories at the start of the study to the target of 20%. At the end of the first year, their fat consumption was 24% of calories, and by the sixth year it had inched back up to 29%.
Biostatistician Ross Prentice of the Fred Hutchinson Cancer Research Center in Seattle said that lower adherence to the diet than planned was why he believed the results of the study were not definitive.
The study also did not differentiate between good and bad fats, and the women did not take specific measures to reduce calories, control blood pressure and increase exercise -- all of which are now recognized as key ingredients of successful programs to preserve health.
Prentice cautioned that the subjects were all “very healthy women who were already following most of the [government’s] dietary guidelines,” so their ability to cut risk by lowering fat may have been low. “Unhealthy women may gain more benefit.”
Marion Nestle, professor of nutrition, food studies and public health at New York University, said she would interpret the study cautiously because she saw many flaws in its methods. One crucial factor, she said, is that the food-intake questionnaire, in which the women recorded their consumption, is “probably inaccurate.”
The women in the low-fat group weighed about 170 pounds and reported a consumption of 1,500 calories per day -- compared with the 2,000 calories a day of a typical diet -- with minor weight loss. “Something is wrong with this picture,” she said
The study did hint at some possible benefits from reducing fat intake. Women who ate the most fats at the beginning of the study and had the greatest reduction in intake had the lowest risk of breast cancer.
Those who achieved the lowest levels of fat consumption -- less than 10% of their calories from animal fats -- had the lowest risk of heart disease. And those who reduced fat intake had a lower incidence of colon polyps and adenomas, generally considered to be precursors of colorectal cancer.
In each of those cases, however, the reductions were not statistically significant, meaning that they could have occurred by chance.
It is possible that the average of eight years that the women in the study have been followed is too little time to see an effect on cancer, said Dr. Rowan T. Chlebowski of the Los Angeles Biomedical Institute, a study coauthor.
“I’m cautiously optimistic that, with a few more years of follow-up, there may be something,” particularly for breast cancer, he said.
Chlebowski reported last year in a study of about 3,000 women who had recovered from breast cancer that a low-fat diet substantially reduced the risk of reoccurrence. The women in that study were able to achieve lower levels of fat intake, however, “perhaps because they were more motivated,” he said.
Concluded Nestle: “My advice is simple, and these studies do not change it: Eat less, move more, avoid junk food, and eat plenty of fruits and vegetables.”
