Effects of 24-Hour Diet- or Exercise-Induced Energy Availability Manipulations on Substrate Utilization and Performance

Purpose: To examine sex-based differences in substrate oxidation, postprandial metabolism, and performance in response to 24-hour manipulations in energy availability (EA), induced by manipulations to energy intake (EI) or exercise energy expenditure (EEE). Methods: In a Latin Square design, 20 endurance athletes (10 females using monophasic oral contraceptives and 10 males) undertook five trials, each comprising three consecutive days. Day one was a standardized period of high EA; EA was then manipulated on day two; post-intervention testing occurred on day three. Day two EA was low/high/higher EA (LEA/HEA/GEA) at 15/45/75 kcal·kg-1FFM·day-1, with conditions of LEA and HEA separately achieved by manipulations of either EI or EEE (LEA REST/EX vs. HEAREST/EX). On day three, fasted peak fat oxidation during cycling and two-hour postprandial (high carbohydrate and energy meal) metabolism were assessed, alongside several performance tests: Wingate, countermovement jump (CMJ), squat jump (SJ), isometric mid-thigh pull (IMTP), and the Stroop Color and Word Test. Results: Highest peak fat oxidation occurred under LEA induced by exercise (p<0.01), with no difference between sexes. Postprandial glucose (p<0.01) and insulin (p<0.05) responses were highest across both sexes when LEA was induced by diet. Relative peak and mean power throughout the Wingate, alongside CMJ height did not differ between EA conditions (p>0.05), while SJ height was lower during GEA than both LEAREST (p=0.045) and HEAEX (p=0.016). IMTP peak force and the Stroop effect did not change with altered EA (p>0.05). Conclusions: Acute (24-hour) exercise-induced LEA influenced fasted substrate oxidation more than diet-induced LEA, while 24 hours of LEA did not impair strength/power, sprint capacity, or cognitive performance. Finally, the responses to EA manipulations did not differ between sexes.