Feasibility and metabolic effects of a 5:2 fasting intervention in women with breast cancer during radiotherapy

Abstract

Abstract Purpose Obesity and insulin resistance appear to worsen prognosis of breast cancer patients. We conducted a feasibility study to test a 5:2 fasting regime in breast cancer patients undergoing radiotherapy. The intervention was rated as beneficial if it would be able to reduce fat mass while significantly improving insulin sensitivity. Methods A total of 13 non-metastatic breast cancer patients were recruited and instructed to completely abstain from food on two non-consecutive days (minimum 24 h) per week during radiotherapy. Body composition was measured weekly by bioimpedance analysis. Blood parameters were assessed before and at the end of radiotherapy. The product of triglycerides and glucose was used as a proxy for insulin sensitivity. A control group on an unspecified standard diet was assigned by propensity score matching. Results A total of twelve patients completed the study. Three patients reported side effects during fasting which were mild (grade 1). Two patients reported feeling bad while fasting, whereas five had a generally good or very good feeling. The fasting group experienced an average decrease of approximately 200 g body mass (p < 0.0001), 200 g (p = 0.002) fat mass and 100 g muscle mass (p = 0.047) per week, resulting in absolute reductions of 2.45 ± 1.19 kg body mass, 1.5 ± 1.6 kg fat mass and 0.7 ± 0.4 kg muscle mass. There was no improvement in insulin sensitivity and other markers of metabolic health except for gamma-glutamyltransferase which decreased by -7 ± 8 U/l. There was also no indication that 5:2 fasting protected against acute skin toxicity. Conclusions 5:2 fasting is safe and feasible for breast cancer patients during radiotherapy and suitable to significantly reduce fat mass, but beneficial metabolic effects could not be confirmed. To improve these results, future studies could combine 5:2 fasting with carbohydrate restriction, increased protein intake and/or exercise. Trial registration Registered on ClinicalTrials.gov under NCT05861362 on May 12, 2023 (retrospectively registered; https://clinicaltrials.gov/ct2/show/NCT05861362).