Nutrient timing

Nutrient timing guidelines are based on the observation that certain nutrients taken at particular times surrounding exercise can improve athletic performance and training adaptations.

Nutrient intake is not only necessary for use as fuel during exercise but also necessary for recovery, tissue repair, muscle growth, bone remodelling, immune function, good mood, etc.

Generally speaking, you can divide 3 stages: pre, during and post. However, for many athletes there is a blurring of stages as the post-exercise period from one session becomes the pre-exercise period of the next session.

Nutrient intake is essential in the pre and post stages, and in some cases during sessions. But it’s not enough with eating and/or drinking to satiety. What you should consume, how much and when depends on a number of factors including the type, intensity and duration of exercise.

Thus, the term nutrient timing describes the strategy in which certain nutrients are taken at specific times relative to exercise sessions to improve performance and/or adaptations to acute and chronic exercise.

Nutrient timing guidelines

Pre-exercise

This is the stage in which fuel for performance becomes critical. The main fuels for exercising muscles in sessions lasting more than a few minutes are carbohydrate (CHO) and fatty acids (FA). Even the leanest individuals have plenty of FA stores in adipose (fat) tissue. On the other hand, CHO availability depends on glycogen stores (in liver, muscle and other tissues) and direct intake. Therefore, this is the stage in which CHO intake becomes important. CHO consumed hours before the session will be mainly stored as glycogen, and CHO consumed in the minutes prior to exercise will be mainly utilised as fuel.

CHO consumed in combination with essential amino acids (EAA) or protein (PRO) before exercise can also help increase muscle protein synthesis, recovery and adaptations from training.

Finally, CHO plays a role in immune function. This is especially important when performing long duration, intense exercise, as it negatively affects the immune system via a variety of mechanisms.

During exercise

The requirement for intra-exercise fuel depends on the type and duration of exercise. Typically, training or competition sessions of moderate to high intense exercise lasting more than 60 minutes will warrant nutrient intake, in particular CHO to replenish glycogen stores and keep blood glucose levels.

Again, combining CHO and PRO can have some advantages, including:

  • an equivalent performance improvement with lower doses of CHO, which can help minimise gastrointestinal distress sometimes produced by large CHO doses
  • a reduction in muscle protein breakdown
  • a potential reduction in central nervous system fatigue

Post-exercise

The post-exercise stage is where growth and recovery happen. This includes the glycogen stores and muscle protein are rebuilt after an exercise bout. The combination of PRO and CHO seems to be synergistic for both processes. The quantity and quality of PRO is especially important after resistance and high intensity endurance exercise, in which muscle protein breakdown is the highest.

What about hydration?

Hydration is a whole can of worms and will not be discussed in this article.

The guidelines

The table below shows a compilation of best practices for intake of carbohydrate (CHO), protein (PRO) and other nutrients based on the type, duration and intensity of exercise. Note that it doesn’t cover all types of exercise, nor mixed modalities. Also note that most amounts are specified as ranges, because the actual requirement will vary depending on several factors, including intake in previous meals, glycogen stores, individual physiology, etc.

How important is nutrient timing, really?

As seen above, nutrient timing can make a difference in athletic performance and recovery. However, it is not always possible for athletes to follow the guidelines due to multiple limiting factors:

  • time and ability to prepare, transport and/or procure food and beverages
  • time to consume meals especially when completing multiple training or competition sessions plus work, study and/or family commitments
  • practicality of consuming food or drinks during exercise bouts
  • palate fatigue
  • gastrointestinal tolerance
  • health conditions
  • weight requirements

Therefore, athletes should strive to follow nutrient timing guidelines when possible, but place more importance in meeting their energy and nutrient requirements.

References

  1. Burke LM, Castell LM, Casa DJ, Close GL, Costa RJS, Melin AK, et al. International association of athletics federations consensus statement 2019: Nutrition for athletics. Vol. 29, International Journal of Sport Nutrition and Exercise Metabolism. Human Kinetics Publishers Inc.; 2019. p. 73–84.
  2. Arent SM, Cintineo HP, McFadden BA, Chandler AJ, Arent MA. Nutrient timing: A garage door of opportunity? Vol. 12, Nutrients. MDPI AG; 2020. p. 1–19.

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