Do Low-Fat Diets Curb Disease?

The theory that eating less fat can help prevent disease suffered a setback today with the release of a large-scale study that failed to show such a diet lowered older women's risk of breast and colon cancer, and heart disease.

Health researchers are not giving up on the low-fat message, however, and say the new study has too many shortcomings to provide a clear answer on the health benefits of eating less fat.

The new study was conducted by researchers with the Women's Health Initiative, a $415 million National Institutes of Health study of nearly 49,000 postmenopausal women.

They analyzed the health of women who ate a diet lower in fat and higher in vegetables, fruits and grains over an eight-year period. The low-fat group was compared with women on a regular diet.

At the end of the study, the low-fat group did not show a significantly lower risk of developing breast cancer, colon cancer or heart disease and strokes.

Results of the study were published in several articles in today's issue of the Journal of the American Medical Association.

Questions About Study's Limitations

In e-mails and phone interviews that ABC News conducted with more than 50 specialists in heart disease, cancer and nutrition, questions were raised about the shortcomings of the study. Among the concerns:

   The study was too short in duration to detect reduction in breast and colon cancer from fat reduction. Eight years is not enough time to see a reduction in cancers that often take decades to develop, experts said.

   The amount of fat reduction was too small. The researchers hoped to get the low-fat dieters to reduce fat intake by 20 percent, but they only achieved, on average, a less than 10 percent reduction. Heart researchers say such a small decrease is unlikely to produce meaningful benefits.

   The researchers simply looked at fat intake in general and did not distinguish between healthy fats like olive oil and unhealthy fats like trans fats, which increase cholesterol.

Fat Does Matter

Whatever the concern, the lackluster findings do not mean people should add more fat to their diets, because some small health benefits were seen in the low-fat group, said Dr. Jacques Rossouw, the Women's Health Initiative project officer.