Comparable Exogenous Carbohydrate Oxidation from Lactose or Sucrose during Exercise

Nutritional Considerations for the Vegan Athlete

Accepting a continued rise in the prevalence of vegan-type diets in the general population is also likely to occur in athletic populations, it is of importance to assess the potential impact on athletic performance, adaptation, and recovery. Nutritional consideration for the athlete requires optimization of energy, macronutrient, and micronutrient intakes, and potentially the judicious selection of dietary supplements, all specified to meet the individual athlete's training and performance goals. The purpose of this review is to assess whether adopting a vegan diet is likely to impinge on such optimal nutrition and, where so, consider evidence based yet practical and pragmatic nutritional recommendations. Current evidence does not support that a vegan-type diet will enhance performance, adaptation, or recovery in athletes, but equally suggests that an athlete can follow a (more) vegan diet without detriment. A clear caveat, however, is that vegan diets consumed spontaneously may induce suboptimal intakes of key nutrients, most notably quantity and/or quality of dietary protein and specific micronutrients (eg, iron, calcium, vitamin B12, and vitamin D). As such, optimal vegan sports nutrition requires (more) careful consideration, evaluation, and planning. Individual/seasonal goals, training modalities, athlete type, and sensory/cultural/ethical preferences, among other factors, should all be considered when planning and adopting a vegan diet.

For Flux Sake: Isotopic Tracer Methods of Monitoring Human Carbohydrate Metabolism During Exercise

Isotopic tracers can reveal insights into the temporal nature of metabolism and track the fate of ingested substrates. A common use of tracers is to assess aspects of human carbohydrate metabolism during exercise under various established models. The dilution model is used alongside intravenous infusion of tracers to assess carbohydrate appearance and disappearance rates in the circulation, which can be further delineated into exogenous and endogenous sources. The incorporation model can be used to estimate exogenous carbohydrate oxidation rates. Combining methods can provide insight into key factors regulating health and performance, such as muscle and liver glycogen utilization, and the underlying regulation of blood glucose homeostasis before, during, and after exercise. Obtaining accurate, quantifiable data from tracers, however, requires careful consideration of key methodological principles. These include appropriate standardization of pretrial diet, specific tracer choice, whether a background trial is necessary to correct expired breath CO2 enrichments, and if so, what the appropriate background trial should consist of. Researchers must also consider the intensity and pattern of exercise, and the type, amount, and frequency of feeding (if any). The rationale for these considerations is discussed, along with an experimental design checklist and equation list which aims to assist researchers in performing high-quality research on carbohydrate metabolism during exercise using isotopic tracer methods.

Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g h-1 versus 90 g h-1 at different ratios

Purpose

This study aimed to investigate whether carbohydrate ingestion during 3 h long endurance exercise in highly trained cyclists at a rate of 120 g h⁻¹ in 0.8:1 ratio between fructose and glucose-based carbohydrates would result in higher exogenous and lower endogenous carbohydrate oxidation rates as compared to ingestion of 90 g h⁻¹ in 1:2 ratio, which is the currently recommended approach for exercise of this duration.

Methods

Eleven male participants (V̇O_2peak 62.6 ± 7 mL kg⁻¹ min⁻¹, gas exchange threshold (GET) 270 ± 17 W and Respiratory compensation point 328 ± 32 W) completed the study involving 4 experimental visits consisting of 3 h cycling commencing after an overnight fast at an intensity equivalent to 95% GET. During the trials they received carbohydrates at an average rate of 120 or 90 g h⁻¹ in 0.8:1 or 1:2 fructose-maltodextrin ratio, respectively. Carbohydrates were naturally high or low in ¹³C stable isotopes enabling subsequent calculations of exogenous and endogenous carbohydrate oxidation rates.

Results

Exogenous carbohydrate oxidation rates were higher in the 120 g h⁻¹ condition (120–180 min: 1.51 ± 0.22 g min⁻¹) as compared to the 90 g h⁻¹ condition (1.29 ± 0.16 g min⁻¹; p = 0.026). Endogenous carbohydrate oxidation rates did not differ between conditions (2.15 ± 0.30 and 2.20 ± 0.33 g min⁻¹ for 120 and 90 g h⁻¹ conditions, respectively; p = 0.786).

Conclusions

The results suggest that carbohydrate ingestion at 120 g h⁻¹ in 0.8:1 fructose-maltodextrin ratio as compared with 90 g h⁻¹ in 1:2 ratio offers higher exogenous carbohydrate oxidation rates but no additional sparing of endogenous carbohydrates. Further studies should investigate potential performance effects of such carbohydrate ingestion strategies.

13C-glucose-fructose labeling reveals comparable exogenous CHO oxidation during exercise when consuming 120 g/h in fluid, gel, jelly chew, or coingestion

We examined the effects of carbohydrate (CHO) delivery form on exogenous CHO oxidation, gastrointestinal discomfort, and exercise capacity. In a randomized repeated-measures design [after 24 h of high CHO intake (8 g·kg^-1) and preexercise meal (2 g·kg^-1)], nine trained males ingested 120 g CHO·h^-1 from fluid (DRINK), semisolid gel (GEL), solid jelly chew (CHEW), or a coingestion approach (MIX). Participants cycled for 180 min at 95% lactate threshold, followed by an exercise capacity test (150% lactate threshold). Peak rates of exogenous CHO oxidation (DRINK 1.56 ± 0.16, GEL 1.58 ± 0.13, CHEW 1.59 ± 0.08, MIX 1.66 ± 0.02 g·min^-1) and oxidation efficiency (DRINK 72 ± 8%, GEL 72 ± 5%, CHEW 75 ± 5%, MIX, 75 ± 6%) were not different between trials (all P > 0.05). Despite ingesting 120 g·h^-1, participants reported minimal symptoms of gastrointestinal distress across all trials. Exercise capacity was also not significantly different (all P > 0.05) between conditions (DRINK 446 ± 350, GEL 529 ± 396, CHEW 596 ± 416, MIX 469 ± 395 s). Data represent the first time that rates of exogenous CHO oxidation (via stable isotope methodology) have been simultaneously assessed with feeding strategies (i.e., preexercise CHO feeding and the different forms and combinations of CHO during exercise) commonly adopted by elite endurance athletes. We conclude that 120 g·h^-1 CHO (in a 1:0.8 ratio of maltodextrin or glucose to fructose) is a practically tolerable strategy to promote high CHO availability and oxidation during exercise.NEW & NOTEWORTHY We demonstrate comparable rates of exogenous CHO oxidation from fluid, semisolid, solid, or a combination of sources. Considering the sustained high rates of total and exogenous CHO oxidation and relative lack of gastrointestinal symptoms, consuming 120 g CHO·h^-1 appears to be a well-tolerated strategy to promote high CHO availability during exercise. Additionally, this is the first time that rates of exogenous CHO oxidation have been assessed with feeding strategies (e.g., coingestion of multiple CHO forms) typically reported by endurance athletes.

New Horizons in Carbohydrate Research and Application for Endurance Athletes

The importance of carbohydrate as a fuel source for exercise and athletic performance is well established. Equally well developed are dietary carbohydrate intake guidelines for endurance athletes seeking to optimize their performance. This narrative review provides a contemporary perspective on research into the role of, and application of, carbohydrate in the diet of endurance athletes. The review discusses how recommendations could become increasingly refined and what future research would further our understanding of how to optimize dietary carbohydrate intake to positively impact endurance performance. High carbohydrate availability for prolonged intense exercise and competition performance remains a priority. Recent advances have been made on the recommended type and quantity of carbohydrates to be ingested before, during and after intense exercise bouts. Whilst reducing carbohydrate availability around selected exercise bouts to augment metabolic adaptations to training is now widely recommended, a contemporary view of the so-called train-low approach based on the totality of the current evidence suggests limited utility for enhancing performance benefits from training. Nonetheless, such studies have focused importance on periodizing carbohydrate intake based on, among other factors, the goal and demand of training or competition. This calls for a much more personalized approach to carbohydrate recommendations that could be further supported through future research and technological innovation (e.g., continuous glucose monitoring). Despite more than a century of investigations into carbohydrate nutrition, exercise metabolism and endurance performance, there are numerous new important discoveries, both from an applied and mechanistic perspective, on the horizon.

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.

Carb-conscious: the role of carbohydrate intake in recovery from exercise

PURPOSE OF REVIEW

The present review summarized evidence on the role of carbohydrates in recovery from exercise within the context of acute and chronic effects on metabolism and performance.

RECENT FINDINGS

Recent studies demonstrate that, in contrast to recovery of muscle glycogen stores, the recovery of liver glycogen stores can be accelerated by the co-ingestion of fructose with glucose-based carbohydrates. Three recent studies suggest this can extend time-to-exhaustion during endurance exercise tests. However, periodically restricting carbohydrate intakes during recovery from some training sessions to slow the recovery of liver and muscle glycogen stores may, over time, result in a modest increase in the ability to oxidize fat during exercise in a fasted state. Whether this periodized strategy translates into a performance advantage in the fed state remains to be clearly demonstrated.

SUMMARY

To maximize recovery of glycogen stores and the capacity to perform in subsequent endurance exercise, athletes should consider ingesting at least 1.2 g carbohydrate per kilogram body mass per hour - for the first few hours of recovery - as a mixture of fructose and glucose-based carbohydrates. However, if a goal is increased capacity for fat oxidation, athletes should consider restricting carbohydrate intakes during recovery from some key training sessions.

VIDEO ABSTRACT

http://links.lww.com/COCN/A15.