Effects of Time-Restricted Eating on Aerobic Capacity, Body Composition, and Markers of Metabolic Health in Healthy Male Recreational Runners: A Randomized Crossover Trial.

Background: Optimal nutrition is highly valuable for athletes aiming at maintaining or improving body composition and sports performance. When combined with structured exercise, time-restricted energy intake may represent an effective nonpharmacological approach to achieving these results.

Objective: The aim of this study was to investigate the effects of 4 weeks of time-restricted eating (TRE) vs 4 weeks of habitual diet on aerobic capacity, body composition, and metabolic health in 18- to 30-year-old men accustomed to endurance running.

Design: This trial used a randomized-crossover study design. Participants completed graded exercise tests, body composition scans, and fasting blood samples before and after each intervention condition.

Participants/setting: Sixteen male physical education students were recruited and enrolled in the study from the Faculty of Human Kinetics-University of Lisbon in September 2020, in Lisbon, Portugal. One participant was excluded after 1 week because of a lack of adherence to the study protocol. Therefore, 15 participants completed the study and were involved in the final analysis.

Intervention: During the TRE condition, participants consumed two to three meals within an 8-hour eating window (between 1:00 and 9:00 pm). Only water, tea, and coffee (without caloric additives) were permitted to be consumed in the remaining 16 hours per 24-hour period. During the non-TRE condition, participants consumed their habitual diet without any timing restrictions. The order of the TRE intervention and the habitual diet condition was randomized and counterbalanced, and participants served as their own controls. The participants followed a structured training routine during each dietary condition.

Main Outcome Measures: Body composition variables, indices of running aerobic capacity, and markers of metabolic health were assessed.

Statistical Analyses Performed: One-way repeated-measures analysis of variance and covariance were performed to analyze differences between conditions and time with each intervention.

Results: Neither condition elicited observed changes in total body mass, fat mass, or fat-free mass between time points. Moreover, no significant changes were observed for markers of metabolic health. Significant improvements were obtained with both conditions for the first ventilatory threshold, maximum oxygen uptake (VO), and velocity at VO (P < 0.05).

Conclusions: Four weeks of endurance running and TRE, compared with 4 weeks of endurance running and a habitual diet, in healthy trained 18- to 30-year-old male recreational runners did not result in observed differences in total body mass, fat mass, or fat-free mass. In addition, TRE did not offer any additional benefit for improving submaximal or peak exercise capacity in this population.