Energy balance

Adjuvant chemotherapy for breast cancer causes weight gain primarily through reduced physical activity and sarcopenic obesity (fat gain with lean mass loss), not through increased caloric intake.

If you are gaining weight during breast cancer chemotherapy, do not blame yourself for eating too much. Research shows that caloric intake does not significantly increase during this time. Instead, the weight gain is driven by a drop in physical activity and a loss of muscle mass (sarcopenic obesity). The most effective intervention is to increase physical activity, specifically resistance training for the legs, to preserve muscle and prevent fat gain.