Dose-Response Oxidation of Ingested Phytoglycogen during Exercise in Endurance-Trained Men.

BACKGROUND: Phytoglycogen (PHY; PhytoSpherix; Mirexus Biotechnologies), a highly branched polysaccharide extracted from sweet corn, has considerable potential for exercise oxidation due to its low viscosity in water, high water retention, and exceptional stability. OBJECTIVES: Using gas chromatography-isotope ratio mass spectrometry, we investigated dose-response oxidation of ingested PHY during prolonged, moderate-intensity exercise. METHODS: Thirteen men (≥1 y endurance-training experience, ≥6 d·wk-1, ∼1-1.5 h·d-1; age, 25.7 ± 5.5 y; mass, 79.3 ± 10.0 kg;  V̇O2max, 59.9 ± 5.5 mL·kg-1·min-1; means ± SDs) cycled for 150 min (50% maximal watt output) while ingesting PHY concentrations of 0.0% (0.0 g·min-1), 3.6% (0.5 g·min-1), 7.2% (1.0 g·min-1), 10.8% (1.5 g·min-1), or 14.4% (2 g·min-1) in water (2100 mL) (n = 7-10/dose). Substrate oxidation was determined using stable-isotope methods and indirect calorimetry. RESULTS: PHY oxidation plateaued between 60 and 150 min of exercise and increased (P < 0.001) from 0.49 to 0.72 g·min-1 with 0.5- and 1.0-g·min-1 doses without further increases (0.76 and 0.73 g·min-1; P > 0.05) with 1.5 or 2 g·min-1. Peak PHY oxidation (0.84 ± 0.04 g·min-1) occurred in the final 30 min of exercise with 2 g·min-1. Exercise blood glucose was greater (5.1 mmol·L-1) with 1.0-, 1.5-, and 2-g·min-1 doses compared with that of 0.5 (4.7 mmol·L-1) or 0.0 g·min-1 (4.2 mmol·L-1) (P < 0.0001). Gastrointestinal distress was minimal except with 2 g·min-1 (P < 0.001). CONCLUSIONS: In male endurance athletes, PHY oxidation plateaued at 0.72-0.76 g·min-1 during 150 min of cycling at 50% Wmax (peak oxidation of 0.84 g·min-1 occurred during the final 30 min). This trial was registered at clinicaltrials.gov as NCT02909881.

Indicator amino acid oxidation protein requirement estimate in endurance-trained men 24 h postexercise exceeds both the EAR and current athlete guidelines.

Despite studies indicating increased protein requirements in strength-trained or endurance-trained (ET) individuals, the Institute of Medicine has concluded that "no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise," and the controversy regarding exercise effects on protein requirements continues. The objective of this study was to determine the dietary protein requirement of healthy young ET men (≥1 yr training experience) 24 h post exercise (to minimize any acute effects of the previous training session) by measuring the oxidation of ingested l-[1-13C]phenylalanine to 13CO2 in response to graded intakes of protein (indicator amino acid oxidation technique). Eight men [maximal oxygen consumption 64.1 ml·kg-1·min-1 (SD 3.7)] were each studied 24 h postexercise repeatedly with protein intakes ranging from 0.3 to 3.5 g·kg-1·day-1. Protein was fed as an amino acid mixture based on the protein pattern in egg, except for phenylalanine and tyrosine, which were maintained at constant amounts across all protein intakes. For 2 days before the study day, all participants consumed 1.6 g protein·kg-1·day-1. The estimated average requirement (EAR) for protein was determined by applying a nonlinear mixed-effects change-point regression analysis to F13CO2 (label tracer oxidation in 13CO2 breath), which identified a breakpoint in the F13CO2 in response to the graded amounts of protein. The EAR for protein and the upper 95% confidence interval were 2.1 and 2.6 g·kg-1·day-1, respectively. These data suggest that the protein EAR for ET men 24 h postexercise exceeds the Institute of Medicine EAR and established athlete guidelines by ~3.5- and 1.3-fold, respectively.

Indicator Amino Acid-Derived Estimate of Dietary Protein Requirement for Male Bodybuilders on a Nontraining Day Is Several-Fold Greater than the Current Recommended Dietary Allowance.

Background: Despite a number of studies indicating increased dietary protein needs in bodybuilders with the use of the nitrogen balance technique, the Institute of Medicine (2005) has concluded, based in part on methodologic concerns, that "no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise."Objective: The aim of the study was to assess the dietary protein requirement of healthy young male bodybuilders ( with ≥3 y training experience) on a nontraining day by measuring the oxidation of ingested l-[1-13C]phenylalanine to 13CO2 in response to graded intakes of protein [indicator amino acid oxidation (IAAO) technique].Methods: Eight men (means ± SDs: age, 22.5 ± 1.7 y; weight, 83.9 ± 11.6 kg; 13.0% ± 6.3% body fat) were studied at rest on a nontraining day, on several occasions (4-8 times) each with protein intakes ranging from 0.1 to 3.5 g · kg-1 · d-1, for a total of 42 experiments. The diets provided energy at 1.5 times each individual's measured resting energy expenditure and were isoenergetic across all treatments. Protein was fed as an amino acid mixture based on the protein pattern in egg, except for phenylalanine and tyrosine, which were maintained at constant amounts across all protein intakes. For 2 d before the study, all participants consumed 1.5 g protein · kg-1 · d-1 On the study day, the protein requirement was determined by identifying the breakpoint in the F13CO2 with graded amounts of dietary protein [mixed-effects change-point regression analysis of F13CO2 (labeled tracer oxidation in breath)].Results: The Estimated Average Requirement (EAR) of protein and the upper 95% CI RDA for these young male bodybuilders were 1.7 and 2.2 g · kg-1 · d-1, respectively.Conclusion: These IAAO data suggest that the protein EAR and recommended intake for male bodybuilders at rest on a nontraining day exceed the current recommendations of the Institute of Medicine by ∼2.6-fold. This trial was registered at clinicaltrials.gov as NCT02621294.

Cycling Time Trial Performance 4 Hours After Glycogen-Lowering Exercise Is Similarly Enhanced by Recovery Nondairy Chocolate Beverages Versus Chocolate Milk.

Postexercise chocolate milk ingestion has been shown to enhance both glycogen resynthesis and subsequent exercise performance. To assess whether nondairy chocolate beverage ingestion post-glycogen-lowering exercise can enhance 20-km cycling time trial performance 4 hr later, eight healthy trained male cyclists (21.8 ± 2.3y, VO2max = 61.2 ± 1.4 ml·kg-1·min-1; M ± SD) completed a series of intense cycling intervals designed to lower muscle glycogen (Jentjens & Jeukendrup, 2003) followed by 4 hr of recovery and a subsequent 20-km cycling time trial. During the first 2 hr of recovery, participants ingested chocolate dairy milk (DAIRYCHOC), chocolate soy beverage (SOYCHOC), chocolate hemp beverage (HEMPCHOC), low-fat dairy milk (MILK), or a low-energy artificially sweetened, flavored beverage (PLACEBO) at 30-min intervals in a double-blind, counterbalanced repeated-measures design. All drinks, except the PLACEBO (247 kJ) were isoenergetic (2,107 kJ), and all chocolate-flavored drinks provided 1-g CHO·kg body mass-1·h-1. Fluid intake across treatments was equalized (2,262 ± 148 ml) by ingesting appropriate quantities of water based on drink intake. The CHO:PRO ratio was 4:1, 1.5:1, 4:1, and 6:1 for DAIRYCHOC, MILK, SOYCHOC, and HEMPCHOC, respectively. One-way analysis of variance with repeated measures showed time trial performance (DAIRYCHOC = 34.58 ± 2.5 min, SOYCHOC = 34.83 ± 2.2 min, HEMPCHOC = 34.88 ± 1.1 min, MILK = 34.47 ± 1.7 min) was enhanced similarly vs PLACEBO (37.85 ± 2.1) for all treatments (p = .019) These data suggest that postexercise macronutrient and total energy intake are more important for same-day 20-km cycling time trial performance after glycogen-lowering exercise than protein type or protein-to-carbohydrate ratio.