In this study, researchers compared resistance training combined with time-restricted eating (TRE) to habitual eating on fat and fat-free mass and maximum and explosive force production in healthy, trained individuals.
The non-pharmacological approach of increasing muscle mass and decreasing fat mass is common for improving health outcomes and athletic performance. Diet and exercise often combine when people seek to alter their body composition. Intermittent fasting has become increasingly popular due to its potential health benefits for body composition, lipidemia, glycemia, insulinemia, blood pressure, and inflammation.
In contrast to continuous energy restriction, intermittent fasting is marked by a chronic reduction in daily energy intake of up to 40%, regardless of the frequency of meals. Additionally, intermittent fasting has been shown to produce higher levels of compliance than continuous energy restriction, and this may be especially pertinent for long-term observation.
This crossover trial initially included 18 male students who were well acquainted with resistance training, had normal blood pressure (120/80 mmHg), and did not take any medications. Inclusion was restricted to healthy males with prior experience in resistance training (consistently performing more than three sessions/week for the past three years).
Over several different visits, all participants were assessed at approximately the same time of day (between 6.00 a.m. and 8.00 a.m.). Each dietary intervention (TRE vs regular diet) was combined with resistance training in a structured and supervised fashion, with measurements taken before and after thirty days.
TRE involved an 8-hour eating window, non-TRE involved a habitual meal pattern, and participants served as their controls. The diet order was randomized and counterbalanced. In addition, participants underwent performance strength tests and body composition scans at baseline and post-intervention.
The participants followed a structured training routine during each dietary intervention (four sets of maximum repetitions at 85% 1RM in five dynamic exercises, three times/week); both interventions elicited decreases in fat mass but not in fat-free mass.
It was found that non-TRE training was associated with better lower body jump performance than TRE training (controlling for baseline values as covariates). In contrast, training with TRE elicited higher values of peak force and dynamic strength index for upper body training.
In conclusion, there were no significant differences between interventions in already trained young males in terms of fat mass and fat-free mass. Further, while TRE and resistance training can benefit individuals focusing on developing high-speed strength performances at the upper body level, they do not apply to individuals focusing on developing lower body strength.
Over four weeks of intervention, resistance training had the greatest impact on decreasing fat mass instead of a diet. In addition, resistance training has long been known to affect resting energy expenditure chronically.
As a result of acute resistance training, excess post-exercise oxygen consumption increases, and the respiratory exchange ratio shifts towards values compatible with fat utilization. The combination of all these factors, regardless of dietary pattern, reduces fat mass after resistance training.