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.

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). Forty-six women with overweight/obesity (age = 35 ± 10 years, BMI = 29.1 ± 2.3 kg/m2) 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. Final WL (MΔ = 4.7 [95% confidence interval 4.2, 5.2] kg, 5.9%) did not differ between IER and CER (interaction P = 0.307). During IER, feed-day EI did not differ from baseline and was lower in the final week compared to week 2 (MΔ = 295 [81, 509] kcal, P = 0.004). Daily hunger was greater on fast compared to feed days (MΔ = 15 [10, 21] mm, P < 0.001), but food cravings did not differ. Light PA was lower on fast relative to feed days (MΔ = 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 interactions P ≤ 0.034). 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.