Obesity Abstracts

Background: Intermittent fasting involves alternating between periods of severely restricted and unrestricted energy intake. Physical activity energy expenditure (PAEE) is reduced during, and energy intake is elevated after, a period of energy restriction, but whether these are altered in anticipation of energy restriction is currently unknown. The aim of this study was to assess whether energy intake and PAEE are altered in the 24 h before, as well as during and at the first meal following, a 24 h period of severe energy restriction.

Methods: In randomised, counterbalanced order, 14 lean males completed two trials spanning 3-days. Upon arrival on day 1, participants were informed which diet they would receive on day 2 of the trial; either an energy balanced diet providing 100% (2755 (159) kcal; EB), or an energy restricted diet providing 25% (691 (42) kcal; ER), of their estimated energy requirements. Ad-libitum energy intake was then determined at researcher-weighed breakfast (0830 h–0900 h), lunch (1230 h–1300 h), mid-afternoon (14:00–18:00) and dinner (1930 h–2000 h) meals. On day 2, participants were provided their allocated diet, consuming this outside the laboratory according to guidance provided by researchers. On day 3, ad-libitum energy intake was determined at breakfast (0830 h–0900 h). PAEE was measured throughout via integrated heart-rate and accelerometry monitors.

Results: Energy intake was 6% greater on day 1 (259 (92) kcal; P<0.05) and 14% greater at breakfast on day 3 (176 (59) kcal; P<0.05) during ER compared to EB. PAEE was 156 (67) kcal lower on day 1 (P<0.05) and 239 (105) lower on day 2 (P<0.05) during ER compared to EB. Excluding the study intervention, compensatory changes in energy intake and PAEE resulted in an 830 (123) kcal more positive energy balance during ER (P<0.0001), accounting for 40% of the energy deficit induced by the dietary intervention on day 2.

Conclusions: This study demonstrates that compensatory changes in energy intake and PAEE occur before, during and after an acute 24 h period of severe energy restriction, which favour the restoration of energy balance. Whether these changes remain with chronic intermittent fasting warrants further study.

Keywords: Intermittent fasting, energy balance, eating behaviour, physical activity

Disclosures: none.