Energy restriction and the prevention of breast cancer.

Energy restriction (ER) to control weight is a potential strategy for breast cancer prevention. The protective effects of habitual continuous energy restriction (CER) and weight loss on breast tumour formation have been conclusively demonstrated in animal studies over the past 100 years, and more recently in women using data from observational studies and bariatric surgery. Intermittent energy restriction (IER) and intermittent fasting (IF) are possible alternative preventative approaches which may be easier for individuals to undertake and possibly more effective than standard CER. Here, we summarise the available data on CER, IER and IF with special emphasis on their potential for breast cancer prevention. In animals, IER is superior or equivalent to CER with the exception of carcinogen-induced tumour models when initiated soon after carcinogen exposure. There are no human data on IER and breast cancer risk, but three studies demonstrated IER and CER to be equivalent for weight loss. IF regimens also reduce mammary tumour formation in animal models and also led to weight loss in human subjects, but have not been directly compared with CER. Animal and some human data suggest that both IER and IF may differ mechanistically compared with CER and may bring about greater reduction in hepatic and visceral fat stores, insulin-like growth factor 1 (IGF-1) levels and cell proliferation, and increased insulin sensitivity and adiponectin levels. Although IER and IF were first studied 65 years ago, we conclude that further studies are required to assess their values compared with CER.