Combined intermittent fasting and exercise intervention in patients with metastatic, hormone receptor-positive breast cancer (FastER): a pilot study.

Purpose: With limited lifestyle interventions available for women with metastatic breast cancer, we aimed to evaluate feasibility of a combined prolonged overnight fasting and exercise intervention in women with hormone receptor-positive metastatic breast cancer initiating treatment.

Methods: Women with metastatic breast cancer initiating endocrine therapy plus targeted therapy were included in a single-arm pilot trial testing a combined 12-week prolonged nightly fasting and exercise intervention. Fasting goals included abstaining from calorie intake after 8 pm and fasting for 13 + hours 6 days per week; weekly exercise goals were 120 min of home-based aerobic exercise and 2 sessions of resistance exercise. Primary outcome was feasibility; secondary outcomes included patient-reported outcomes, cardiorespiratory fitness, and physical functioning. Measures were collected at baseline and 12-week time points.

Results: Thirty-one women enrolled, and 27 completed both timepoint assessments. The feasibility goal for enrollment was met with 80% of participants enrolled within the first year. The fasting intervention was well tolerated, with 74.1% of women meeting the fasting goal. Only 40.7% of women achieved the aerobic exercise goal, and 18.5% met the strength training goal. Participants experienced a significant increase in quality of life post-intervention, with improvements in emotional (+ 8.3 ± 14.2 point; p = 0.003), cognitive (+ 4.9 ± 17.2 point; p = 0.04), social functioning (+ 8.6 ± 18.1 point; p = 0.02), dyspnea (- 12.3 ± 28.0 point; p = 0.002), and insomnia (- 16.0 ± 25.1 point; p < 0.001).

Conclusion: This pilot study provides insights into the feasibility, safety, and preliminary efficacy of a 12-week combined fasting and exercise intervention in women with metastatic breast cancer initiating treatment.