Effect of an acute fast on energy compensation and feeding behaviour in lean men and women

AIM: Humans appear to defend against energy deficit to a greater extent than energy surplus. Severe dietary energy restriction resulting in 5 - 30% weight loss often leads to hyperphagia and weight regain in lean subjects. However, the period of time over which fasting is often endured in Western society are far shorter, similar to1 - 2 days. This study examined how a 36 h fast effected the subsequent day's energy and nutrient intake in a group of 24 healthy, lean men and women.

METHOD: Subjects underwent two 2 day treatments, termed 'fast' and 'maintenance'. During the 'fast' treatment, subjects were fed a maintenance diet on the day prior to the fast (day -1) to prevent overeating. They then consumed non-energy drinks only, from 20:00 h on day - 1 to 08:00 h on day 2 (ad libitum feeding day), thus fasting for 36 h. On the 'maintenance' protocol, subjects received a maintenance diet throughout day 1. Throughout day 2 they had ad libitum access to a range of familiar foods, which were the same for both treatments. Body weight, blood glucose and respiratory quotient were used as compliance checks. Hunger was monitored on day's - 1, 1 and 2 for the fast treatment only.

RESULTS: On day 2, average energy intake was 10.2 vs 12.2 MJ/day (s.e.d. 1.0) on the post-maintenance and post-fast periods, respectively (P = 0.049). Subjects altered feeding behaviour, in response to the fast, only at breakfast time, selecting a higher-fat meal (P < 0.005). Compared to day - 1, motivation to eat was elevated during the fast (P < 0.05). This continued until breakfast was consumed during the re-feeding period (day 2), when values then returned to baseline.

CONCLUSION: These data suggest that a 36 h fast, which generated a negative energy balance of - 12 M), did not induce a powerful, unconditioned stimulus to compensate on the subsequent day.