A question many patients with cancer ask is if diet can improve their prognosis or prevent recurrence. A low-fat diet has been shown to prevent or improve many conditions, including breast cancer. This fact sheet explores the data from studies evaluating the effect of a low-fat diet on breast cancer outcomes.

Supportive Data

The WINS trial (ClinicalTrials.gov Identifier: NCT00002564) randomly assigned 2437 women with early-stage breast cancer to an intervention or control group. The intervention group received intensive dietary intervention with a target of 15% of energy from fat, whereas the control group received minimal counseling. The counselors did not discuss weight reduction.1,2

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The baseline energy from fat was 29.6% and 29.2% in the intervention and control groups, respectively, and was 20.3% and 29.2%, respectively, at 12 months. This change was maintained for at least 5 years.

Fruit intake increased in the intervention group, and serum fatty acid analysis suggested that the fatty acid profiles were improved.

Relapse-free survival (RFS), the primary endpoint, was 24% higher in the intervention group (events, 9.8%) compared with the control group (events, 12.4%; hazard ratio [HR], 0.76; 95% CI, .60-.98; P = .077 log-rank, P = .034). Women with hormone receptor–negative disease experienced an even greater benefit, with a 42% higher RFS at 8 years (RFS, 9.5%) with the intervention compared with the control counseling.

The authors noted, however, that body weight was significantly lower in the intervention group (P = .005) after 60 months and could have influenced the results.

In the prospective, Collaborative Women’s Longevity Study (CWLS) population study, 4441 women with breast cancer aged 20 to 79 completed a food frequency questionnaire and were followed for a mean of 5.5 years for all-cause and breast cancer–related mortality.3

There was a significantly greater risk of all-cause mortality among women with the highest intake of saturated (HR, 1.41; 95% CI, 1.06-1.87; Ptrend = .03) and trans fat (HR, 1.78; 95% CI, 1.35-2.32; Ptrend = .01) intake compared with those with the lowest intakes. There was a trend toward higher saturated and trans fats intake and increased breast cancer–related mortality, but this association was not significant. Total fat intake was not associated with all-cause or breast cancer–related mortality.

A meta-analysis of 3 of the studies described in this fact sheet,1,3,7 which included 9966 women with breast cancer, concluded that a low-fat diet reduced the risk of breast cancer recurrence by 23% (HR, 0.77; 95% CI, 0.63-0,94; P = .009) and all-cause mortality by 17% (HR, 0.83; 95% CI, 0.69-1.00; P = .05).4

More recently, an analysis of the Women’s Health Initiative (WHI) trial evaluated the role of dietary intervention with breast cancer outcomes. This trial randomly assigned 48,835 postmenopausal women without breast cancer to dietary intervention with a goal of fat intake of 20% of energy and increased fruits, vegetables, and grains, or the usual diet. This analysis identified 1764 women in the cohort who developed breast cancer.5

Though there was a trend of fewer breast cancer–related deaths among the women during the 8.5-year intervention compared with the usual dietary group, the finding was not significant (0.016% vs 0.024% per year; HR, 0.67; 95% CI, 0.43-1.06; P = .08).  All-cause mortality after breast cancer, however, was significantly less in the intervention group vs the usual diet group (0.025% vs 0.038% per year; HR, 0.65; 95% CI, 0.45-0.94; P = .02).

During the 16-year follow-up period, breast cancer–related mortality was significantly less in the intervention group (0.085% per year) compared with the usual diet group (0.11% per year; HR, 0.82; 95% CI, 0.70-0.96; P = .01).