Overall, making comprehensive dietary changes in line with a Mediterranean diet did not reduce women’s risk for breast cancer recurrence or metastasis. However, women at high risk for recurrence who made the greatest improvements in their diet quality demonstrated a 41% lower risk for recurrence compared with peers who made the fewest improvements.
A growing body of evidence suggests that a better dietary quality may improve survival among patients with breast cancer, but whether diet impacts breast cancer–specific mortality remains controversial.
To better understand the relationship between diet and breast cancer outcomes, investigators recruited 1542 women with breast cancer who had undergone surgical resection in the past 5 years and were considered high risk for recurrence.
All women received general recommendations for cancer prevention, while the intervention group received active support to adhere to a macro-Mediterranean-style diet, which encourages mainly consuming whole grains, legumes, and high-fiber vegetables and discourages eating foods high in saturated and trans fats, processed meats, and foods and beverages high in sugar.
Diet was assessed at baseline, 1 year, and every few months in subsequent years via food frequency diaries. Compliance with dietary recommendations for the whole cohort was assessed using a Dietary Index developed for the trial.
In addition to diet, women in the diet intervention group were encouraged to maintain moderate-to-intense physical activity — 30 minutes, on average, each day — and received pedometers to track steps, aiming for 10,000 per day.
Over 5 years of follow-up, the rate of breast cancer recurrence did not differ between women in the diet intervention group and those in the control group. Overall, 95 of 769 women in the intervention group and 98 of 773 in the control group had a breast cancer recurrence (hazard ratio [HR], 0.99).
When evaluating outcomes in the entire cohort, looking at everyone’s level of compliance with dietary recommendations, women who adhered the most to the dietary guidelines had a 41% lower recurrence risk compared with women who adhered the least (HR, 0.59).
The greatest protective effect among women who demonstrated high compliance occurred in those with ER-positive cancers (HR, 0.42) and those with ER-positive cancers who received tamoxifen (HR, 0.30).
This intervention trial “did not confirm the hypothesis that a comprehensive dietary modification reduces breast cancer recurrence and metastases,” but when looking at compliance to the Mediterranean diet overall, the analysis did find “a significantly better prognosis” for women with the best adherence.
The study, with first author Franco Berrino, MD, PhD, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy, was published online October 17 in Clinical Cancer Research.
The study relied on self-reported dietary data. No dietary instrument was used to estimate nutrient intake and the Dietary Index developed for the trial remains unvalidated.
The study was supported by the Italian Department of Health, the Associazione Italiana per la Ricerca sul Cancro, and the Vita e Salute Foundation. The authors report no relevant financial relationships.
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