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We designed a non randomized prospective controlled trial on caloric restriction (CR) or intermittent fasting (IF) in overweight-obese patients with breast or prostate cancer referred for curative radiotherapy.

Patients who meet inclusion criteria underwent CR or IF depending on the patient's preference (according to their lifestyle). CR consisted in reduction in 25% of the basal caloric intake and IF of suppressing intake for at least 16 hours. All patients had to begin their intervention at least 2 weeks before radiotherapy. The primary objective was to investigate the feasibility of a nutritional intervention concurrent with radiation therapy. The adherence was defined as a 5% reduction in the body weight. Secondary objectives included change in anthropometric measures (weight and waist circumference) and serum levels of glucose, insulin and lipids. We also evaluated acute toxicity and quality of life reports (not included in this primary report).

From April 2021 and September 2021 we recruited 16 patients. One patient withdrew from the trial before treatment and 1 patient did not receive radiotherapy. Of the 14 patients available for analysis, 12 were women with breast cancer and luminal ductal carcinoma was the most common histologic subtype. 7/12 received some kind of chemotherapy (neoadjuvant, adjuvant or both) and 8/12 received endocrine therapy. 9/12 underwent CR and 3/12 IF. All patients underwent whole breast radiotherapy (± regional nodal irradiation) and 7/12 simultaneous integrated boost to the tumor bed up to 45,75 Gy. 2/14 patients were men with operated prostate cancer and Gleason score 6 and 7. All of them had initiated androgen deprivation therapy, underwent IF and received a dose of radiotherapy 51 Gy in 17 fractions to the prostate bed or equivalent EQD2. 

At the end of October 2021, 8/12 patients had completed 12 weeks follow up. There was a weight loss of 4,2 kg in average, and 6/8 patients lost 5% or more of the initial weight (true adherence). Mean reduction in waist circumference was 4,9 cm and serum levels of glucose, triglycerides and insulin showed mean reductions of 1.3 mg/dL, 24.2 mg/dL and 2.1 uU/mL respectively.

Implementing a nutritional intervention like CR o IF in patients receiving radiotherapy is feasible and effective in reducing body weight and waist circumference and showed to improve serum levels of glucose, insulin and lipids in a short period of time.