ESTES PARK, COLO. – Perhaps the least-known finding of the landmark Women’s Health Initiative was the complete failure of a structured low-fat diet intervention to lower the risks of coronary heart disease, stroke, or colon cancer.
"This has gotten very little press. But the results made me very happy because it gave me one less thing to worry about, which is eating a low-fat diet. It doesn’t seem to have the same magnitude of effect in women as it does in men," Dr. Nanette Santoro said at a conference on internal medicine sponsored by the University of Colorado.
Dr. Nanette Santoro
The Women’s Health Initiative Randomized Controlled Dietary Modification Trial involved 48,835 postmenopausal women aged 50-79 at 40 U.S. centers who were randomized 40/60 to a low-fat diet intervention or a control group.
During a mean follow-up of 8.1 years, the diet intervention and control groups didn’t show any significant differences in rates of coronary heart disease (hazard ratio, 0.97); stroke (1.02); or cardiovascular disease (0.98) (JAMA 2006;295:655-66).
Similarly, the event-rate curves for cardiovascular outcomes as well as for colon cancer in the intervention and control arms were virtually identical the entire time, with no hint of either early or late benefit for the low-fat diet (JAMA 2006;295:643-54).
There was a nonsignificant trend for less invasive breast cancer in the low-fat diet group, where the annualized incidence rate was 0.42%, a 9% relative risk reduction compared with the 0.45% rate in controls (JAMA 2006;295:629-42).
"So if there’s any possible benefit to a low-fat diet, there might be some for breast cancer," commented Dr. Santoro, professor and chair of the department of ob.gyn. at the university.
The diet intervention entailed an intensive behavioral modification program with 18 group sessions during year 1 and quarterly maintenance sessions thereafter, with supplemental individualized contact. The goal was to reduce dietary fat intake by boosting consumption of fruits and vegetables to at least five servings daily, along with at least six servings of grains daily. Weight loss goals weren’t part of the study, which was designed in the 1990s before the obesity epidemic was apparent.
The intervention was effective in terms of accomplishing lasting dietary change. At baseline, fat accounted for about 38% of total daily energy intake. After 1 year, this figure dropped to 24% in the diet intervention arm. At year 6, fat accounted for 29% of daily energy intake in the diet group compared with 37% in controls, a difference Dr. Santoro called "huge" in light of the enormous number of participants and the women’s diverse ethnicities and backgrounds.
The intervention group averaged 3.6 servings per day of fruits and vegetables at baseline and 4.9 by year 6, compared with 3.8 in controls. Efforts to increase consumption of grains were unsuccessful, however. The intervention group averaged 4.7 servings per day at baseline and 4.3 at year 6, compared with 3.8 in controls.
The Women’s Health Initiative Randomized Controlled Dietary Modification Trial was funded by the National Heart, Lung, and Blood Institute. Dr. Santoro reported that she has a research grant from Bayer.