# A randomised controlled trial of short-term 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

## TL;DR

This study compares two diet strategies for weight loss and improving health in women with obesity at risk of breast cancer.

## Contribution

It is the first randomized trial comparing intermittent versus continuous energy restriction on fat stores and insulin resistance in this specific population.

## Key findings

- Both intermittent and continuous energy restriction led to similar reductions in weight and fat stores.
- Fasting insulin resistance improved with continuous energy restriction but not consistently with intermittent energy restriction.
- Both groups showed comparable reductions in fat-free mass and resting metabolic rate.

## Abstract

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.

Premenopausal women with obesity [n = 28] were randomised to 8 weeks of 25% energy restriction: IER [2 days/week 600 kcal/2511kj and 5 days/week Mediterranean diet] versus CER [7 days/week Mediterranean diet]. Changes in body weight, hepatic, pancreatic and calf intramuscular fat fractions [magnetic resonance spectroscopy] and insulin resistance [HOMA and oral glucose tolerance test], body fat and fat free mass [bioelectrical impedance], resting metabolic rate [RMR, indirect calorimetry] and lipids (total, LDL, HDL cholesterol and tryglycerides) were assessed during the energy restricted and normal eating days of IER compared to CER.

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 fat fraction mean [SD]: IER − 74.1[22.0]% CER − 51.4[34.8]%, pancreatic fat fraction mean [SD]: IER − 41.1[35.4]% CER − 30.8[25.4]% and calf intramuscular fat fraction mean [SD]: IER − 8.9[27.4]% CER − 2.3[24.1]%. 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. The IER and CER groups had comparable reductions in FFM IER − 1.2[1.4] kg CER − 1.2[1.0] kg and RMR IER − 380[594] kj CER − 594[670] kj. Both groups had reductions in total and HDL cholesterol and triglyceride and maintained LDL.

IER and CER have comparable reductions in weight and ectopic fat stores, fat free mass and RMR and lipids. The clinical significance of the failure to maintain beneficial insulin sensitivity across the week with IER is not known and requires further study.

ISRCTN 10,803,394 Registration date 12/01/2015.

The online version contains supplementary material available at 10.1186/s40795-025-01181-4.