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

Purpose: The objective of this study is to examine sex-based differences in substrate oxidation, postprandial metabolism, and performance in response to 24-h manipulations in energy availability (EA), induced by manipulations to energy intake or exercise energy expenditure.

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 1 was a standardized period of high EA; EA was then manipulated on day 2; postintervention testing occurred on day 3. Day 2 EA was low/high/higher EA (LEA/HEA/GEA) at 15/45/75 kcal·kg -1 FFM·d -1 , with conditions of LEA and HEA separately achieved by manipulations of either energy intake or exercise energy expenditure (LEA REST/EX vs HEA REST/EX ). On day 3, fasted peak fat oxidation during cycling and 2-h postprandial (high carbohydrate and energy meal) metabolism were assessed, alongside several performance tests: Wingate, countermovement jump, squat jump, isometric mid-thigh pull, 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 countermovement jump height did not differ between EA conditions ( P > 0.05), whereas squat jump height was lower during GEA than both LEA REST ( P = 0.045) and HEA EX ( P = 0.016). Isometric mid-thigh pull peak force and the Stroop effect did not change with altered EA ( P > 0.05).

Conclusions: Acute (24-h) exercise-induced LEA influenced fasted substrate oxidation more than diet-induced LEA, whereas 24 h of LEA did not impair strength/power, sprint capacity, or cognitive performance. Finally, the responses to EA manipulations did not differ between sexes.