Fasting diet could boost breast cancer therapy

A fasting-mimicking diet combined with hormone therapy has the potential to help treat breast cancer, according to new study published in the journal Nature.

In studies on mice and in two small breast cancer clinical trials, researchers found that the fasting-mimicking diet reduces blood insulin, insulin-like growth factor 1 (IGF1) and leptin. In mice, these effects appear to increase the power of the cancer hormone drugs tamoxifen and fulvestrant and delay any resistance to them. The results from 36 women treated with the hormone therapy and fasting-mimicking diet are promising, but researchers say it is still too early to determine whether the effects will be confirmed in large-scale clinical trials.

The researchers said the two small clinical trials are feasibility studies that showed promising results, but they are in no way conclusive. They believe the results support further clinical studies of a fasting-mimicking diet used in combination with endocrine therapy in hormone-receptor-positive breast cancer.

The scientists also contributed to a recent clinical study of 129 breast cancer patients conducted with the University of Leiden. The results, published last month in Nature Communications, appeared to show increased efficacy of chemotherapy in patients receiving a combination of chemotherapy and a fasting-mimicking diet.

In the two clinical trials, patients with hormone-receptor-positive breast cancer receiving estrogen therapy along with cycles of a fasting-mimicking diet seemed to experience metabolic changes like those observed in mice. These changes included a reduction in insulin, leptin and IGF1 levels, with the last two remaining low for extended periods. In mice, these long-lasting effects are associated with long-term anti-cancer activity, so further studies in humans is needed.

The data also suggest that in mice, the fasting-mimicking diet appears to prevent tamoxifen-induced endometrial hyperplasia, a condition in which the endometrium becomes abnormally thick. The study authors believe this potential use of the fasting diet should be explored further, given the prevalence of this side effect of tamoxifen and the limited options for preventing it.

Approximately 80 percent of all breast cancers express estrogen or progesterone receptors. The most common forms of hormone therapy for these breast cancers work by blocking hormones from attaching to receptors on cancer cells or by decreasing the body's hormone production. Endocrine therapy is frequently effective in these hormone-receptor-positive tumors, but the long-term benefits are often hindered by treatment resistance.

Several clinical trials are now investigating the effects of the fasting-mimicking diets in combination with different cancer therapies.