After a Century, it's time to turn the page on understanding of lactate metabolism and appreciate that lactate shuttling is an important component of intermediary metabolism in vivo. Cell-Cell and intracellular Lactate Shuttles fulfill purposes of energy substrate production and distribution as well as cell signaling under fully aerobic conditions. Recognition of lactate shuttling came first in studies of physical exercise where the roles of driver (producer) and recipient (consumer) cells and tissues were obvious. Moreover, the presence of lactate shuttling as part of postprandial glucose disposal and satiety signaling has been recognized. Mitochondrial respiration creates the physiological sink for lactate disposal in vivo. Repeated lactate exposure from regular exercise results in adaptive processes such as mitochondrial biogenesis and other healthful circulatory and neurological characteristic such as improved physical work capacity, metabolic flexibility, learning, and memory. The importance of lactate and lactate shuttling in healthful living is further emphasized when lactate signaling and shuttling are dysregulated as occur in particular illnesses and injuries. Like a Phoenix, lactate has risen to major importance in 21 st Century Biology.

Endurance athletes use nutritional guidelines and supplements to improve exercise performance and recovery. However, use is not always based on scientific evidence of improved performance, which type of athlete would benefit most, or the optimal dose and timing of a particular supplement. Health professionals that give advice to athletes need to target their recommendations on the energy systems and muscle fiber types used for the athlete's sporting event, the goal of the training block, the time of the competitive season, and the characteristics and food preferences of the individual athlete. This review aims to summarize the most current research findings on the optimal calorie, carbohydrate, and protein intake for athlete health, performance, and recovery. We also summarized new findings on fluid intake and the optimal dose and timing of beetroot and caffeine supplementation on time trial performance in endurance athletes.

Background: Time restricted Feeding (TRF) is a dietary pattern utilized by endurance athletes, but there is insufficient data regarding its effects on performance and metabolism in this population. The purpose of this investigation was to examine the effects of a 16/8 TRF dietary pattern on exercise performance in trained male endurance runners. Methods: A 4-week randomized crossover intervention was used to compare an 8-h TRF to a 12-h normal diet (ND) feeding window. Exercise training and dietary intake were similar across interventions. Runners completed a dual-energy X-ray absorptiometry (DXA) scan to assess body composition, a graded treadmill running test to assess substrate utilization, and ran a 10 km time trial to assess performance. Results: There was a significant decrease in fat mass in the TRF intervention (−0.8 ± 1.3 kg with TRF (p = 0.05), vs. +0.1 ± 4.3 kg with ND), with no significant change in fat-free mass. Exercise carbon dioxide production (VCO2) and blood lactate concentration were significantly lower with the TRF intervention (p ≤ 0.02). No significant changes were seen in exercise respiratory exchange ratio or 10 km time trial performance (−00:20 ± 3:34 min:s TRF vs. −00:36 ± 2:57 min:s ND). Conclusion: This investigation demonstrated that adherence to a 4-week 16/8 TRF dietary intervention decreased fat mass and maintained fat-free mass, while not affecting running performance, in trained male endurance runners.

Calorie restriction (CR) is a common approach to inducing negative energy balance. Recently, time-restricted feeding (TRF), which involves consuming food within specific time windows during a 24h day, has become popular owing to its relative ease of practice and potential to aid in achieving and maintaining a negative energy balance. TRF can be implemented intentionally with CR, or TRF might induce CR simply due to the time restriction. This review focuses on summarizing our current knowledge on how time-restricted feeding (TRF) and continuous caloric restriction (CR) affect gut peptides that influence satiety. Based on peer-reviewed studies, in response to CR there is an increase in the orexigenic hormone ghrelin and reduction in fasting leptin and insulin. There is likely a reduction in glucagon-like-peptide-1 (GLP-1), peptide-YY (PYY), and cholecystokinin (CCK), albeit the evidence for this is weak. Following TRF, unlike CR, fasting ghrelin decreased in some TRF studies, while showing no change in several others. Further, a reduction in fasting leptin, insulin, and GLP-1 has been observed. In conclusion, when other determinants of food intake are held equal, the peripheral satiety systems appeared to be somewhat similarly affected by CR and TRF with regard to leptin, insulin and GLP-1. But unlike CR, TRF did not appear to robustly increase ghrelin suggesting different influences on appetite with a potential decrease of hunger following TRF when compared to CR. However, there are several established and novel gut peptides that have not been measured within the context of CR and TRF, and studies that have evaluated effects of TRF are often short-term, with non-uniform study designs, and highly varying temporal eating patterns. More evidence and studies addressing these aspects are needed to draw definitive conclusions.