ASCO Annual Meeting
ASCO Annual Meeting
May 15, 2019
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Low-fat diet reduces risk for breast cancer death among postmenopausal women

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Photo of Rowan Chlebowski
Rowan T. Chlebowski

Postmenopausal women reduced their breast cancer mortality risk by adopting a low-fat diet that included increased consumption of vegetables, fruits and grains, according to results from a randomized Women’s Health Initiative clinical trial scheduled for presentation at ASCO Annual Meeting.

“The impetus for a study of dietary fat intake and eating patterns came a quarter of a century ago, when we noticed country-to-country differences in fat intake and breast cancers; countries with low fat intake had lower breast cancer frequency. The question was, were these factors related?” study author Rowan T. Chlebowski, MD, PhD, FASCO, chief of the division of medical oncology and hematology at Harbor-UCLA Medical Center and researcher at the center’s Los Angeles Biomedical Research Institute, said during a press cast. “The observational studies have provided mixed results, and so this randomized clinical trial started as a component of the Women’s Health Initiative.”

Chlebowski and colleagues evaluated the influence of a low-fat diet on breast cancer incidence and outcomes among 48,835 postmenopausal women aged 50 to 79 years seen at 40 participating U.S. centers. Participants had no history of breast cancer and consumed a diet in which fat comprised 32% or more of total daily calories.

Between 1993 and 1998, the researchers randomly assigned the women to a usual-diet control group (60%) or to a dietary intervention group (40%), in which the goal was to decrease fat intake to 20% of energy or less and include one daily serving or more of a vegetable, fruit and grain. In the usual-diet control group, fat accounted for 32% or more of participants’ daily calories.

Women followed the balanced, low-fat intervention diet for about 8.5 years.

Results showed the intervention resulted in a significant decrease in daily fat intake to 25% or less of daily calories — most women did not reach the 20% goal — as well as increased consumption of fruit, vegetables and grains, with modest (3%) average weight loss (all P < .001).

The intervention group incurred 8% fewer breast cancers than the control group during the dietary intervention and fewer breast cancer deaths, but the difference in these rates was not significant.

However, the intervention group demonstrated a 15% reduced risk for death of any cause after a breast cancer diagnosis, with decreases in risk during the intervention (HR = 0.65; 95% CI, 0.45-0.95) and through a cumulative median follow-up of 16.1 years.

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With long-term, cumulative follow-up of 19.6 years and 3,374 cases of breast cancer diagnosed among participants, the intervention group continued to demonstrate significant decrease in deaths after breast cancer (n = 1,011; HR = 0.85; 95% CI, 0.74-0.96), and showed a significant reduction in deaths of breast cancer (n = 383; HR = 0.79; 95% CI, 0.64-0.97).

Additionally, metabolic syndrome score identified a subgroup of women at high risk for death from breast cancer who were more likely to benefit from the dietary intervention. The 9.3% of women with three or four components of metabolic syndrome had a statistically significant 69% (HR = 0.31; 95% CI, 0.14-0.69) reduced risk for breast cancer mortality.

“Adoption of a low-fat dietary pattern reduces the risk for death from breast cancer in postmenopausal women,” Chlebowski said. “It’s a diet we feel is achievable by many, because it represents dietary moderation and was achieved by 19,000 women in the study.” – by Jennifer Byrne

Reference:

Chlebowski RT, et al. Abstract 520. Scheduled for presentation at: ASCO Annual Meeting; May 31-June 3, 2019; Chicago.

Disclosures: NCI provided funding for this study. Chlebowski reports consultant/advisory roles with Amgen, AstraZeneca, Genentech, Novartis and Pfizer; speakers bureau roles with AstraZeneca and Novartis; and patents, royalties and other intellectual property, stock and ownership interests with Metastat. Please see the abstract for all other authors’ relevant financial disclosures.