Article Review #2:  Carbohydrates for Training and Competition

Burke LM, Hawley JA, Wong SH, Jeukendrup AE. Carbohydrates for training and competition. Journal of Sports Sciences, 2011;29(S1):S17-S27

Article Summary:

There is an enormous amount of interest and research in the subject of carbohydrates as fuel and the relationship to performance in sports. “Carbohydrate availability” is often discussed in regards to timing of ingestion relating to exercise, as well as the overall daily intake. This subject generates significant interest in athletes and those involved in their care.

This article reviews carbohydrates for daily refueling and recovery, acute refueling strategies, glycemic index as well as intake during and after prolonged exercise. The key findings are:

  • When training at high intensity, daily carbohydrate intakes should match fuel needs of training and restoration. This starts at 3-5 g/kg/day to as high as 8-12 g/kg/day.
  • If the period of refueling is less than 8 hours, time is of the essence – begin refueling as soon as practical; early refueling will be enhanced by higher rate of carbohydrate intake in small and frequent feedings.
  • Adding protein when carbohydrate intake is sub-optimal will enhance glycogen storage.
  • There remains debate on manipulating the glycemic index – this still needs to be individualized to the specific event and the athlete.
  • In events longer than 2-3 hours; higher intakes of carbohydrates, up to 90 g/hr., require products providing “multiple transportable carbohydrates” (glucose:fructose in 2:1 mixtures) which can help achieve higher rates of oxidation of carbohydrate.
  • During shorter events, 45-75 minutes, mouth rinsing of a carbohydrate mixture or intake of a very small amount of carbohydrate can improve performance through a “non-metabolic” role involving the central nervous system.

In addition, low carbohydrate intake, or “train low/compete high”, may present a new paradigm for training adaptations. Recent research examining the effect of exercising at low glycogen levels has shown that both a surplus and a lack of glycogen with exercise can trigger positive training adaptations. A low carbohydrate diet has also been shown to increase the ability to oxidize fat during exercise, but may impair carbohydrate utilization with high-intensity exercise.

Some athletes already periodize their carbohydrate availability for training sessions. By design or accident, many workout sessions are undertaken with reduced carbohydrate stores. Whether implementing additional ‘‘train-low’’ strategies to increase the training adaptation leads to enhanced performance in well-trained individuals remains unclear, and further research is warranted.

Questions for Discussion:

An important question is whether training with reduced glycogen stores should be exploited, and how can that be accomplished without having negative effects on the athlete’s performance?

Similar to this article by Burke and colleagues, the recent article by Volek, Noakes and Phinney (2014), “Rethinking fat as a fuel for endurance exercise,” makes a strong argument for using our largest fuel source, fat. Utilizing fat would cause a shift to fatty acids and ketones as the primary fuel for endurance athletes, which is known as keto-adaptation. There is a need to better understand what level of carbohydrate restriction is appropriate and what the exact composition of the diet should consist of to fully benefit from keto-adapation.

The review presents what may be an entirely different model of fueling athletic performance, “dietary periodization”, which includes periods of training in a low carbohydrate environment. On one hand, the review gives key recommendations for our athletes in regards to training and restoration of glycogen and fuel for performance. On the other, it asks, what might be the best training programs using carbohydrate restriction and dietary periodization?

This will be a fascinating area of future research.

Written By: Michael Reeder, D.O.

Reviewed By: Felice Beitzel, Ph.D.

Additional Reference:

Volek JS, Noakes T, Phinney SD. Rethinking fat as fuel for endurance exercise. European Journal of Sport Science, 2014