Plain language summary
Adequate nutrition is important for elite athletes, as nutrient availability influences energy expenditure, body composition, performance and exercise-induced immune responses. Time-restricted eating (TRE) is a form of intermittent fasting that has received much interest in recent years. Previous research of TRE suggested beneficial effects on performance in untrained individuals, by allowing weight loss whilst maintaining muscle functions. These qualities are of interest for endurance cyclists hence the authors of this study sought to investigate the impact of TRE in elite cyclists. Sixteen under-23 year old, elite cyclists were randomly assigned to eat within a TRE window of 8-hr or 15hr window during a 4-week, high-level endurance training phase. Both groups consumed their full estimated energy needs and markers such as fat and fat-free mass, VO2 max, basal metabolism, blood counts, anabolic hormones and inflammatory markers were measured. As a result, TRE produced weight loss, improved body composition and increased peak power output in relation to body weight without compromising aerobic performance. Furthermore, the TRE pattern proved helpful in mitigating some of the exercise-induced suppressions of the immune system. The authors concluded that TRE could be considered as part of a performance nutrition plan in endurance athletes. Particularly where there is a need to reduce body fat mass or for the management of training-induced depression of the immune system and associated respiratory infection susceptibility. This can be of clinical relevance in the support of endurance athletes.
BACKGROUND Although there is substantial interest in intermittent fasting as a dietary approach in active individuals, information regarding its effects in elite endurance athletes is currently unavailable. The present parallel randomized trial investigated the effects of a particular intermittent fasting approach, called time-restricted eating (TRE), during 4 weeks of high-level endurance training. METHODS Sixteen elite under-23 cyclists were randomly assigned either to a TRE group or a control group (ND). The TRE group consumed 100% of its estimated daily energy needs in an 8-h time window (from 10:00 a.m. to 6:00 p.m.) whilst energy intake in the ND group was distributed in 3 meals consumed between 7:00 a.m. and 9:00 p.m. Fat and fat-free mass were estimated by bioelectrical impedance analysis and VO2max and basal metabolism by indirect gas analyzer. In addition, blood counts, anabolic hormones (i.e. free testosterone, IGF-1) and inflammatory markers (i.e. IL-6, TNF-α) were assessed. RESULTS TRE reduced body weight (- 2%; p = 0.04) and fat mass percentage (- 1.1%; p = 0.01) with no change in fat-free mass. Performance tests showed no significant differences between groups, however the peak power output/body weight ratio (PPO/BW) improved in TRE group due to weight loss (p = 0.02). Free testosterone and IGF-1 decreased significantly (p = 0.01 and p = 0.03 respectively) in TRE group. Leucocyte count decreased in ND group (p = 0.02) whilst the neutrophils-to-lymphocytes ratio (NLR) decreased significantly (p = 0.03) in TRE group. CONCLUSIONS Our results suggest that a TRE program with an 8-h feeding window elicits weight loss, improves body composition and increases PPO/BW in elite cyclists. TRE could also be beneficial for reducing inflammation and may have a protective effect on some components of the immune system. Overall, TRE could be considered as a component of a periodized nutrition plan in endurance athletes. TRIAL REGISTRATION This trial was retrospectively registered at clinicaltrials.gov as NCT04320784 on 25 March 2020.