Four weeks of 16/8 time restrictive feeding in endurance trained male runners decreases fat mass, without affecting exercise performance

Authors: TOVAR, ASHLEY - University Of California; RICHARDSON, CHRISTINE - University Of California, Davis; Keim, Nancy; VAN LOAN, MARTA - Retired ARS Employee; DAVIS, BRIAN - Uc Davis Medical Center; CAZZASA, GRETCHEN - California State University

Submitted to: Nutrients
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2021
Publication Date: 8/25/2021
Citation: Tovar, A.P., Richardson, C.E., Keim, N.L., Van Loan, M.D., Davis, B.A., Cazzasa, G.A. 2021. Four weeks of 16/8 time restrictive feeding in endurance trained male runners decreases fat mass, without affecting exercise performance. Nutrients. 13(9). https://doi.org/10.3390/nu13092941.
DOI: https://doi.org/10.3390/nu13092941

Interpretive Summary: Endurance athletes are known to alter macronutrient intake to improve performance prior to competition, but a new nutritional strategy known as time-restricted feeding (TRF) has become popular despite little or no scientific evidence to support use of this regimen. In this study we compared physical performance effects of restricting food intake to TRF of 8 hours with a more normal pattern (ND) allowing 12 hours of eating, in male endurance runners. Using a graded exercise test, a lower production of carbon dioxide and a decrease in blood lactate at the highest exercise intensity was observed with TRF compared to ND. Importantly, the diet patterns did not affect the 10K time trial performance, despite alterations observed with the graded treadmill test. This investigation demonstrated that adherence to a TRF dietary pattern for 4 weeks did not affect running performance in trained male endurance runners.

Technical Abstract: Nutritional strategies, such as periodization of macronutrient intake, have been utilized by athletes to maximize adaptations to their exercise training and optimize performance. Without much evidence, time restricted feeding (TRF) has become a popular dietary pattern among athletes, including endurance runners. Purpose: This study was designed to investigate the effects of a 16/8 TRF dietary pattern on exercise performance in endurance trained male runners. Methods: A randomized crossover intervention was used to compare an 8-hour feeding window (TRF) to a 12-hour feeding window (mimics a normal diet pattern), with the remaining time spent fasting. At the beginning and end of each 4-week intervention runners provided a resting heartrate, completed a graded substrate utilization treadmill running test to analyze exercise metabolism, and ran a 10 km time trial to assess performance. Results: Exercise carbon dioxide production (VCO2) was significantly lower on the TRF diet (p = 0.01) compared to the normal 12-hour feeding pattern. Driven primarily by values at 90% VO2peak, a diet by exercise intensity interaction was seen in blood lactate (p = 0.02), indicating a lower blood lactate from the TRF diet compared to the 12-hour feeding window as intensity increased. No significant changes were seen from either intervention for resting HR, respiratory exchange ratio, or 10km time trial performance. Conclusion: Significant changes to VCO2 and blood lactate during exercise did not translate to an effect on 10 km time trial performance. This investigation demonstrated that adherence to a TRF dietary pattern for 4 weeks did not affect running performance in trained male endurance runners.