Background: Dietary calorie restriction reverses dysglycaemia in type 2 diabetes in proportion to the degree of calorie restriction. There has been much interest in whether the timing of calorie restriction provides additional benefit to such a diet. One possible mechanism is the attenuation of the drop in basal metabolic rate commonly seen within a few weeks of starting an energy restricted diet, a phenomenon known as adaptive thermogenesis. Adaptive thermogenesis drops the calorie requirements of a fasting individual below that expected for weight, thus reducing weight loss during a low-calorie diet.
Aims: To determine if intermittent fasting produces less adaptive thermogenesis compared with continuous daily restriction during a 6-week dietary intervention.
Methods: We conducted a randomised controlled trial in obese men of 79% daily restriction versus an intermittent fast consisting of two days of 25% restriction and 5 days of eucaloric intake per week over 6 weeks. Body composition, resting energy expenditure & anthropometry were measured at baseline 3 weeks and 6 weeks. Secondary outcomes were change in HbA1C, blood pressure, fasting lipids, leptin, ghrelin, adiponectin and thyroid function tests. A general linear mixed model (GLMM) was used for the primary outcome. ANCOVA was used for all secondary outcome variables.
Results: 32 men completed the diet intervention and lost approximately 1 kg per week. Intermittent energy restriction did not alter weight loss or attenuate adaptive thermogenesis. There was a trend toward fat mass reduction with intermittent fasting.
Conclusion: Intermittent fasting does not attenuate adaptive thermogenesis. A GLMM approach is suggested for studies of RCT’s examining adaptive thermogenesis.