Optimized Carbohydrate Fueling to Enhance Physical Performance During Energy Deficit

Overview

This randomized crossover study will examine the effects of consuming isocaloric GLU+FRU or GLU alone on rates of exogenous carbohydrate oxidation during aerobic exercise and physical performance (time trial) under energy balance (BAL) and energy deficit (DEF). Baseline data will be collected on volunteer height, weight, body composition, and V̇O2peak. To ensure volunteers are familiar with exercise protocols, they will complete practice sessions of all exercise before the start of data collection. Exercise and diet will be controlled throughout data collection. To start the protocol volunteers will complete a bout of glycogen normalization on a cycle ergometer followed by 48 hours of refeeding at 100% (BAL) or 50% (DEF) of their energy needs. After the 48 hours of refeeding volunteers will return to the laboratory to complete 80 min of steady-state (60 ± 5% V̇O2peak) exercise on a cycle ergometer. Immediately before and during steady-state exercise, volunteers will consume either 80 g of GLU+FRU (53 g glucose + 27 g fructose) or 80 g GLU. Drinks containing corn-derived crystalline fructose (KRYSTAR® 300, Tate and Lyle Sugars, London, UK) and glucose (CERELOSE®, Ingredion, Westchester, IL, USA) will be prepared by unblinded USARIEM staff. Drinks will be enriched with 13C stable isotopes (Cambridge Isotope Laboratory, Andover, MA, USA) to measure exogenous and plasma carbohydrate oxidation during steady-state exercise. After steady-state exercise, physical performance will be assessed using a graded exercise test on a stationary bike. Indirect calorimetry and breath sampling will be used to determine substrate oxidation during steady-state exercise. Serial blood draws will be collected during each trial to assess isotope enrichments, and circulating substrate/hormone responses. Muscle biopsies will be performed before and after steady-state exercise to assess glycogen status, enzyme activity, and molecular regulation of substrate metabolism. There will be a minimum of 7 days between each carbohydrate metabolism study day.

Periods of energy deficit (DEF) contribute to declines in physical performance during military operations. During DEF, glucose (GLU) supplementation alone is likely an insufficient intervention to enhance physical performance. The lack of an ergogenic effect with GLU consumption during DEF may result from lower glucose uptake and exogenous glucose oxidation in peripheral tissue. As the current carbohydrate beverage base in Meals, Ready-to-Eat (MRE) is derived solely from GLU, an alternative ration product may be needed to enhance physical performance during DEF. Use of multiple transportable carbohydrates, such as glucose plus fructose (GLU+FRU) may be a more effective ration product, as it has been shown to increase rates of exogenous carbohydrate oxidation and improve physical performance compared to GLU. However, previous studies have only been conducted during energy balance (BAL), and the influence of GLU+FRU on substrate oxidation and physical performance compared to GLU during DEF is currently unknown. This randomized crossover placebo controlled double blinded study will examine the effects of consuming GLU compared to GLU+FRU on substrate oxidation and physical performance during metabolically-matched, steady-state exercise during BAL and DEF. Twelve healthy, recreationally active men and women between the ages of 18-39 yrs will be required to complete this study. To start the protocol volunteers will complete a bout of glycogen normalization cycling followed by 48 hours of refeeding at 100% (BAL) or 50% (DEF) of their energy needs. After the 48 hours refeeding volunteers will return to the laboratory and complete 80 min of steady-state (60 ± 5% VO2peak) cycling. Immediately before and during steady-state exercise, volunteers will consume either 80 g of GLU+FRU (53 g glucose + 27 g fructose) or 80 g GLU. Drinks will be enriched with 13C stable isotopes to measure exogenous carbohydrate oxidation during steady-state exercise. After steady-state exercise, aerobic performance will be assessed. Indirect calorimetry and breath sampling will be used to determine substrate oxidation during steady-state exercise. Serial blood draws will be collected during each trial to assess isotope enrichments, and circulating substrate/hormone responses. Muscle biopsies will be performed before and after steady-state exercise to assess glycogen status, enzyme activity, and molecular regulation of substrate metabolism. Volunteers will complete all four trials (BAL: GLU, DEF: GLU, BAL: GLU+FRU, DEF: GLU+FRU) in a randomized order under controlled laboratory conditions at USARIEM. There will be a minimum of 7 days between each carbohydrate metabolism study day.