An exploratory investigation of the impact of 'fast' and 'feed' days during intermittent energy restriction on free-living energy balance behaviours and subjective states in women with overweight/obesity

Background/objectives This controlled-feeding randomised controlled trial examined free-living appetite and physical activity (PA) on 'fast' and 'feed' days during intermittent energy restriction (IER), compared to continuous energy restriction (CER). Subjects/methods Forty-six women with overweight/obesity (age = 35 +/- 10 years, BMI = 29.1 +/- 2.3 kg/m(2)) were randomised to IER (n = 24; alternate fast days at 25% energy requirements and ad libitum feed days) or CER (n = 22; 75% energy requirements daily) to >= 5% weight loss (WL) or up to 12 weeks. Self-reported energy intake (EI; online food record), objectively measured PA (SenseWear Armband) and retrospective daily hunger and food cravings were measured over 7 days at baseline, week 2 and final week. Intent-to-treat analyses were performed using linear mixed models. Results Final WL (M-Delta = 4.7 [95% confidence interval 4.2, 5.2] kg, 5.9%) did not differ between IER and CER (interactionP = 0.307). During IER, feed-day EI did not differ from baseline and was lower in the final week compared to week 2 (M-Delta = 295 [81, 509] kcal,P = 0.004). Daily hunger was greater on fast compared to feed days (M-Delta = 15 [10, 21] mm,P < 0.001), but food cravings did not differ. Light PA was lower on fast relative to feed days (M-Delta = 18 [2, 34] min/day,P = 0.024), with no other differences in PA. Compared to CER, IER increased hunger and led to smaller improvements in craving control (both interactionsP <= 0.034). Conclusions IER fast days were associated with increased free-living hunger and lower light PA compared to feed days, but had no impact on food cravings or self-reported ad libitum daily EI. IER may be less favourable than CER for the free-living day-to-day control of hunger and food cravings.

Automated summary

This study compared the effects of intermittent energy restriction (IER) and continuous energy restriction (CER) on weight loss, appetite, physical activity, and food cravings. The results showed that IER fast days increased hunger and decreased light physical activity compared to feed days, but had no impact on food cravings or self-reported daily intake.