Effects of Time Restricted Feeding on Peak VO2 and Substrate Utilization in Healthy Adults

Abstract

Time Restricted Feeding (TRF) is a type of Intermittent Fasting, which refers to the finite time to intake calories during the day. TRF has become a dietary approach that is used for weight loss and overall health. Individuals that partake in TRF may experience a decrease in peak volume of oxygen uptake (VO2peak) due to minimization of glycolytic stores. To date, few studies have compared the impact of TRF on VO2peak. PURPOSE: The current study aimed to further investigate the metabolic impact of TRF. METHODS: Twenty one participants, ages 18-60, completed an eleven week longitudinal study to examine differences in VO2peak, substrate utilization crossover, and resting substrate utilization. Participants self-reported diet, exercise, sleep, and medications over two separate four week periods. The first four weeks were without TRF and the following four were with TRF. A maximal exercise test and a resting metabolic test were performed three times, four weeks apart from each other. A repeated measures ANOVA was performed to determine within subject differences. A post-hoc analysis was performed to determine the time effect. RESULTS: VO2peak was significantly lower after implementing TRF (p<0.001). The mean pre-test VO2peak was 2.95±0.59 L/min and the non-TRF testing was 3.14±0.68 L/min. During TRF, the mean was 2.76±0.54 L/min. There was a significant difference between the pre-test and TRF (p=0.012). Also, there was a significant difference between non-TRF and TRF (p=0.002). Resting RQ showed a significant increase (p<0.004). The pre-test mean for resting RQ was 0.716±0.071. Non-TRF resting RQ had a mean of 0.736±0.082 and the TRF resting RQ was 0.802±0.097. There was a significant difference between the pre-test and TRF (p=0.010). Substrate utilization crossover showed a significant decrease (p<0.03) in fat usage after TRF implementation. There was a significant difference between the pre-test (123.9±30.1 watts) and TRF (98.8±30.1 watts; p=0.05). CONCLUSION: An earlier crossover of substrate utilization implies a decrease in fat usage and an increase in carbohydrate usage, therefore significantly lowering fat oxidation and VO2peak. Future studies are needed to examine the physiological mechanisms that may lead to shifts in substrate utilization during TRF.