Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot Environments

Abstract

It is the position of Sports Dietitians Australia (SDA) that exercise in hot and/or humid environments, or with significant clothing and/or equipment that prevents body heat loss (i.e., exertional heat stress), provides significant challenges to an athlete’s nutritional status, health, and performance. Exertional heat stress, especially when prolonged, can perturb thermoregulatory, cardiovascular, and gastrointestinal systems. Heat acclimation or acclimatization provides beneficial adaptations and should be undertaken where possible. Athletes should aim to begin exercise euhydrated. Furthermore, preexercise hyperhydration may be desirable in some scenarios and can be achieved through acute sodium or glycerol loading protocols. The assessment of fluid balance during exercise, together with gastrointestinal tolerance to fluid intake, and the appropriateness of thirst responses provide valuable information to inform fluid replacement strategies that should be integrated with event fuel requirements. Such strategies should also consider fluid availability and opportunities to drink, to prevent significant under- or overconsumption during exercise. Postexercise beverage choices can be influenced by the required timeframe for return to euhydration and co-ingestion of meals and snacks. Ingested beverage temperature can influence core temperature, with cold/icy beverages of potential use before and during exertional heat stress, while use of menthol can alter thermal sensation. Practical challenges in supporting athletes in teams and traveling for competition require careful planning. Finally, specific athletic population groups have unique nutritional needs in the context of exertional heat stress (i.e., youth, endurance/ultra-endurance athletes, and para-sport athletes), and specific adjustments to nutrition strategies should be made for these population groups.

Is the gut microbiota bacterial abundance and composition associated with intestinal epithelial injury, systemic inflammatory profile, and gastrointestinal symptoms in response to exertional-heat stress?

“…1,2,6 The bacterial composition along the gastrointestinal tract, 'the gut microbiota', has previously been proposed as an intrinsic exacerbation factor. 1,8 The absence or presence of commensal and (or) pathogenic bacterial groups may contribute to performance implications (e.g., performance test and performance dependant nutritional provisions and status) through debilitating gastrointestinal symptoms, and clinical implications through the development of gastrointestinal and/or inflammatory conditions (e.g., key pathophysiological aspect of ischemia colitis, disease/disorder of the gastrointestinal tract, fatal sepsis and systemic inflammatory response syndrome). [5][6][7] The interaction between the gut microbiota and human biological systems has recently gained research interest and momentum.…”

The 4R’s Framework of Nutritional Strategies for Post-Exercise Recovery: A Review with Emphasis on New Generation of Carbohydrates

“…Rehydration is important, especially in team, endurance or ultra-endurance sports, where in many cases it is not possible to compensate for the loss of fluids and electrolytes that occur during exercise, particularly in hot and humid environments. As a general advise, for quick rehydration, it is recommended the consumption of 150% of the weight lost after exercise over a short recovery period (less than 4 h) [ 22 , 23 ], with a sodium concentration between 20 and 30 mEq·L −1 [ 18 ]. Athletes and practitioners should replenish three cups of fluid per pound of weight lost (~1.5 L·kg −1 ) and to make sure body mass is back up before the next training session.…”

“…However, if the recovery time is less than 12 h, more aggressive rehydration strategies and the use of moisturizing beverages (e.g., glycerol) are required before the next training or competition [ 25 ]. One practical application to improve both the rate of rehydration and total fluid retention following exercise is the ingestion of glycerol [ 22 , 26 ]; however, professional advice is recommended to avoid potential gastrointestinal discomfort with any hyperhydration agent.…”

Post-Exercise Sweat Loss Estimation Accuracy of Athletes and Physically Active Adults: A Review

“…The second goal was to determine if sweat loss estimation trends across multiple conditions were consistent when viewed from a more global perspective. Vast efforts have been made by the scientific community to promote hydration strategies centered on the recognition of individual sweat rates [ 1 , 3 , 4 , 7 ]. However, data from the current study indicate athletes and adults engaging in exercise underestimate sweat losses by around 40–50%.…”

“…Over the last two and a half decades, multiple scientific cohorts and conclaves have devoted extensive efforts to provide physically active individuals with robust guidelines for fluid intake strategies during and in the times between training bouts [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. While some viewpoints have contended that thirst is an adequate indicator and stimulus for proper fluid consumption [ 6 , 8 ], most other guidelines include detailed recommendations for ideal fluid intake practices based on approximate estimates of sweat losses that will be incurred [ 1 , 3 , 4 , 7 ]. There is no lack of original research concerning hydration and physical activity, but one article in particular, Passe et al [ 9 ], piqued the interest of the current authors in regards to whether the more nuanced guidelines have pragmatic value in real world practice.…”