A Randomised Controlled Trial of Intermittent Energy Restriction (IER) Versus Continuous Energy Restriction (CER) on Body Fat Stores and Measures of Insulin Resistance in Women with Obesity at Increased Risk of Breast Cancer

Background Weight loss and energy restriction are potential strategies for reducing cancer risk, particularly if they reduce ectopic body fat and improve insulin resistance. This randomised study compared the effects of intermittent energy restriction (IER) to continuous energy restriction (CER) on hepatic, pancreatic and intramuscular fat, and insulin resistance. Method Premenopausal women with obesity (n=28) were randomised to two months of 25% energy restriction: IER (2 days/week 600 kcal and 5 days/week Mediterranean diet) versus CER (7 days/week Mediterranean diet). Changes in body weight, hepatic, pancreatic and intramuscular fat (magnetic resonance spectroscopy) and insulin resistance (HOMA and oral glucose tolerance test), body fat and muscle mass (bioelectrical impedance), resting metabolic rate (RMR, indirect calorimetry) were assessed during the energy restricted and normal eating days of IER compared to CER. Results 9 IER and 11 CER participants completed the trial. IER and CER had comparable reductions in body weight mean (SD): IER -6.7(1.4) kg CER -6.2(2.9) kg, and reductions in hepatic, pancreatic and intramuscular fat stores. Fasting measures of insulin resistance (HOMA IR, HOMA-β and fasting insulin) reduced in the CER group and with IER when assessed immediately after the two low energy days but were not maintained during normal eating days. There were no changes in 2-hour glucose in either group. Conclusions IER and CER have comparable reductions in weight and ectopic fat stores. The clinical significance of the failure to maintain beneficial insulin sensitivity across the week with IER is not known and requires further study.