Diet Study Shows Little Effect on Disease in Women
The nearly decade-long dietary modification trial of the national Women's Health Initiative (WHI), which tested the effect of a diet low in total fat and high in fruits, vegetables and whole grains, showed that that diet had no statistically significant effect on rates of breast cancer, colon cancer, heart disease and stroke.
Results of the three arms of the trial were published today (Feb. 8, 2006) in three papers in the Journal of the American Medical Association.
The University at Buffalo is one of the 40 WHI clinical trial sites. This dietary modification arm of the WHI included 1,138 Western New Yorkers among the 48,835 postmenopausal women who participated across the U.S.
Jean Wactawski-Wende, Ph.D., UB associate professor of social and preventive medicine, is a co-author on the papers reporting the breast and colon cancer results. Maurizio Trevisan, M.D., professor and dean of the UB School of Public Health and Health Professions, is a co-author on the heart disease paper.
"The women achieved a remarkable change in dietary fat, but not as much as planned," said Wactawski-Wende. "There is no question that a diet low in fat and high in fruits, vegetables and grains is very healthy. This trial tested the diet's effects on specific conditions. The fact that it showed little effect on those specific conditions does not mean that anyone should abandon a proven healthy diet."
Results showed the dietary change group went from 38 percent to 24 percent of calories from total fat in the first year, to 29 percent in the sixth year. The comparison group, in which women followed their regular diets, averaged 35 percent of calories from fat at year one and 37 percent at year six.
Women in both groups started at 35-38 percent of calories from fat. The low-fat diet group also increased their consumption of vegetables, fruits, and grains.
"If we had achieved what we planned, 20 percent of calories from fat, the changes may have reached statistical significance," she said.
"This study has shown us once again that it is very hard to change behavior. However, those who made those greatest reductions in total dietary fat had the greatest benefits."
"On the issue of breast cancer, results indicated that women who started with the highest fat intake and had greater changes in fat intake showed stronger evidence that they could be reducing their risk," Wactawski-Wende said.
Overall results showed that the intervention group achieved a nine-percent reduction in risk of breast cancer, compared to the comparison group.
"This means that, out of 10,000 women, 42 women in the dietary change group and 45 in the comparison group developed breast cancer each year," said Wactawski-Wende. "This difference was not large enough to be statistically significant -- meaning it could have been due to chance. Longer follow-up may be needed to show the effects of diet on cancer risk over time."
There was no overall benefit on heart disease. Noting that the study focused on total fat intake rather than the type of fat, Trevisan said that for heart disease, specific types of fat, such as saturated fat and trans-fats may be more important than total fat."
"In women who achieved the greatest reduction in saturated fat in this study, we saw the greatest benefit on heart disease and certain blood markers," he said.
The study also found that women following this low-fat and somewhat higher carbohydrate diet did not increase their body weight, triglycerides or indicators of increased risk of diabetes, such as blood glucose or insulin levels.
No effect on colorectal cancer was seen but there was a reduction in the number of colon polyps reported.
Women who took part in the dietary modification trial were assigned randomly to the comparison group and the intervention group. The comparison group maintained their usual diet, while the intervention group was asked to decrease fat intake to 20 percent of total calories, increase fruits and vegetables combined to five or more servings per day, and increase grains to six or more servings per day.
Both groups were tracked for an average of 8.1 years.
The WHI diet proved to be safe, the results showed, and is consistent with current U.S. Dietary guidelines. An ongoing five-year follow-up study may help researchers understand the longer term effects of this low fat dietary intervention, the authors noted.