The Women's Intervention Nutrition Study (WINS), a randomised, phase-III trial of 2,437 women previously treated for early-stage breast cancer, looked at the effects of a low-fat diet with a target of 15 per cent of the calorific intake from fats, or a normal diet (30 per cent of calories from fat).
"The WINS results indicate that a lifestyle intervention designed to reduce dietary fat intake can be successfully implemented in women with early-stage, resected breast cancer receiving conventional cancer management in a multicenter clinical trial setting," wrote the researchers Journal of the National Cancer Institute.
Several epidemiological, animal and population-based studies have associated high-fat diets with higher rates of breast cancer, while results from previous trials have been contradictory, possibly because of poor compliance of the participants.
Indeed, the highly publicised Women's Health Initiative (WHI) Dietary Modification Trial involving 48 835 post-menopausal women reported fat intake reductions of eight percent.
The new study, to be published in the December 20 issue of the Journal of the National Cancer Institute recruited the women participants between February 1994 and January 2001. Forty per cent of the women were assigned to the low-fat intervention group, and the remaining 60 per cent carried on eating their normal diet.
After five years of follow-up, lead author Rowan Chlebowski, from the University of California, Los Angeles Medical Center in Torrance reported that the some form of breast cancer relapse occurred in 9.8 per cent of the women in the intervention group, compared to 12.4 per cent in the control group. "Women in the dietary intervention group had a 24 per cent lower risk of relapse than those in the control group," wrote the researchers.
While the target for the dietary intervention was provide 15 per cent of total calories from fat, the women succeeded on reducing fat intake to give 20 per cent of total calories from fats (about 33 grams per day). Women in the control group maintained their baseline intake of between 56 to 57 grams of fat per day (about 30 per cent of total calories).
Chlebowski and co-workers also report that the low-fat group had significant weight loss of, on average, 2.7 kg (6 lbs), compared to the control group.
The researchers note the limitations of the study, particularly the reliance on self-reporting of dietary fat intake. They also caution that body weight reductions documented in the dietary intervention group may have had an effect on breast cancer recurrence, rather than dietary fat intake on its own.
Indeed, a study published in Breast Cancer Research (2005, Vol. 7, pp. R833-R843) reported that young women who lost weight reduced their risk of breast cancer by 50 per cent. However, women who gained weight had a 65 per cent higher risk of breast cancer.
The University of California results also suggest that women with hormone receptor-negative breast cancers may have had the most benefit from the dietary fat reduction/ However, this was not statistically significant
In an accompanying editorial, Anne Thiébaut and colleagues at the National Cancer Institute noted the difficulties of conducting clinical trials with such drastic interventions. "WINS demonstrates that such trials can be successfully conducted… The totality of this evidence will help us better understand the fat-breast cancer connection and ultimately provide more definitive public health recommendations," they wrote.
There are over one million new cases of breast cancer diagnosed every year worldwide, according to the European School of Oncology, with the highest incidence rates found in the Netherlands and the US.
Source: Journal of the National Cancer Institute December 20, 2006, Volume 98, Pages 1767-1776. "Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women's Intervention Nutrition Study (WINS)" Authors: R.T. Chlebowski, G.L. Blackburn, C.A. Thomson, D.W. Nixon, A. Shapiro, M.K. Hoy, et al.
Editorial: Journal of the National Cancer Institute December 20, 2006, Volume 98, Pages 1753-1755. "Dietary Fat and Breast Cancer: Contributions from a Survival Trial" Authors: A.C.M Thiébaut, A. Schatzkin, R. Ballard-Barbash, V. Kipnis