Low-Fat Diets Don't Protect Postmenopausal Women

Trio of studies found no effect on risk of breast and colon cancer, or heart disease

TUESDAY, Feb. 7, 2006 (HealthDay News) -- A large U.S. government study has found that a diet low in fat but high in vegetables, grains and fruits does not reduce the risk of breast cancer, colorectal cancer or cardiovascular disease in postmenopausal women.

The results, the latest from the Women's Health Initiative (WHI), are not likely to be the last word on the subject, however.

"The issue isn't over," said Dr. Jacques E. Rossouw, WHI project officer at the National Heart, Lung, and Blood Institute. "We plan to follow these women for another five years because it's quite possible that a benefit for both breast cancer and colorectal cancer will emerge over time. This is not going to go away."

Added Dr. Michael Thun, vice president of epidemiology and surveillance research at the American Cancer Society: "This is by far the most definitive study showing exactly what it showed -- that a concerted effort to reduce fat intake to 20 percent of total energy over an eight-year period did not reduce the incidence of breast or colorectal cancer in these women. But it's unlikely to end the debate completely."

Previous evidence has suggested that low-fat diets might protect against cancer and heart disease, but no other studies have been this large or this well-designed.

The WHI is a mammoth, 15-year study designed to identify the most common causes of death, disability and poor quality of life in postmenopausal women.

The findings, which appear in three separate papers in the Feb. 8 issue of the Journal of the American Medical Association, involved almost 50,000 postmenopausal women. The women were randomly chosen to follow either a diet with reduced fat (20 percent of total calories) and increased amounts of vegetables and fruits (five or more servings per day) and grains (six or more servings per day), or to a control group that was not asked to change diet. The participants were followed for just over eight years.

The women in the low-fat part of the study had a 9 percent lower risk of breast cancer than women in the control group, but the difference was not statistically significant. Women who started out with a higher fat intake did have a significant reduction in their risk, however, indicating that such a diet might indeed confer a benefit.

The low-fat diet did not reduce the risk for colorectal cancer. Here, however, there was a reduction in the incidence of polyps, a precursor to this type of cancer, leaving open the tantalizing possibility that some benefit may appear later on. "It's possible that with longer-term adherence to such a diet, a benefit might emerge," Rossouw said.

Finally, the low-fat diet did not appreciably reduce the risk of coronary heart disease, stroke or cardiovascular disease. It achieved only modest effects on risk factors for cardiovascular disease, such as triglyceride levels. LDL ("bad") cholesterol levels and diastolic blood pressure were significantly reduced.

It's possible that a diet lower in particular types of fat might show a benefit. "Reducing total fat didn't make any difference to heart disease, but women who chose to reduce their saturated fat or chose to reduce trans fat more within their total fat had a significant reduction," Rossouw said. "With heart disease, it's very clear that total fat isn't enough. We've got to focus on specific types of fat."

Researchers were also interested to note that high intake of carbohydrates did not increase body weight. Rather, it tended to maintain it.

Dr. Elizabeth G. Nabel, director of the National Heart, Lung, and Blood Institute, said at a press briefing Tuesday: "We really think these findings are good news. This study was the most comprehensive study of this kind and the findings are very consistent with current U.S. dietary recommendations about following a diet low in saturated and trans fats and cholesterol, keeping fat calories to about 20 to 35 percent of total calories.

"Its always important when interpreting findings from any study that a woman consult with her physician and we encourage women to do that," she said.

Cardiologists were cautious about the findings.

"We have to be very careful. The last thing I want is someone to go out eating a high-fat, high-calorie diet," said Dr. Nieca Goldberg, chief of women's cardiac care at Lenox Hill Hospital in New York City and a spokeswoman for the American Heart Association. "It's a combination of things that lowers cardiovascular risk. It's no one diet, no one exercise, no one pill." Goldberg is also author of The Women's Healthy Heart Program.

"It would be easy to misinterpret the results of this study," Dr. Robert H. Eckel, president of the heart association, added in a prepared statement. "Reducing the risk of cardiovascular disease is about following an integrated lifestyle program, rather than concentrating solely on dietary composition."

There were other cautionary notes. It's not clear if starting a low-fat diet earlier in life might have conferred a greater reduction in risk. All of the women in the study were postmenopausal when they changed their eating habits.

Despite the somewhat surprising findings, there are still things that experts know can make a difference.

Ways to reduce the risk of breast cancer include maintaining a healthy body weight, avoiding weight gain in adulthood, getting regular physical activity, limiting the consumption of alcoholic beverages and avoiding postmenopausal hormones, Thun said.

As for heart disease, "we have to avoid extremes," Goldberg said. "Really, it's about a balance, how we exercise and how we eat and balance the stress level as well. We need to keep it real. Nobody wants to hear it. We all want the quick fix. Now's the time to say we really need to be balanced about this."

Rossouw said: "The cancer-prevention findings aren't strong enough to say that most women should now go to a low-fat diet, but women already on such a diet can certainly choose to continue, because over time a benefit might emerge. Women who are currently eating a high-fat diet should seriously consider cutting it down. And, for heart disease, reducing total fat isn't enough. You've got to reduce the bad fat and do all the other things you need to do to improve your risk of heart disease."

Ninety percent of the women in the study will be followed for an additional five years, and more examination will be done on the existing data, leaving open the possibility that more specific dietary components might be shown to have an effect on health, experts said.

"We can do a lot more analysis on this data set to systematically investigate these nutrients and their effect on their endpoints," said Barbara Howard, of the Medstar Research Institute and Howard University in Washington, D.C., and one of the WHI investigators.

More information

For more on the Women's Health Initiative, visit the National Institutes of Health.

Related Stories

No stories found.
logo
www.healthday.com