Friday, September 07, 2018

Do you need to have carbs before training?

Many of my clients are confused about whether they ‘need’ to take carbohydrate before training and events.

So, what’s the deal? Is carbohydrate beneficial, neutral, or detrimental when taken before training?

TL;DR – I think that on balance, for many people, carbohydrate is simply not necessary immediately before training and events. My clinical experience has been that many people either a) don’t require additional carbohydrate to ‘boost’ their glycogen stores before training and b) many suffer adverse effects like energy ‘crashes’ during activity if they have large or even moderate amounts of carbohydrate immediately before training.

Key points:
  • Carbs before training inhibit fat usage
  • Carbs before training don’t offer a benefit to training and events < 90 min
  • Low-carb meals previous to training result in longer times to exhaustion (better endurance)
  • Lower-carb, ‘carb-appropriate’ strategies are likely to result in better preservation of glycogen and improved cardiometabolic health and improved fuel usage

Carbohydrate ingestion before exertion is generally associated with improvements in performance for bouts of relatively intensive activity > 90 min but it reduces lipolysis and can lead to hypoglycaemia which can negatively affect performance in some individuals.1-3 It’s also generally unnecessary for bouts of exercise under 90 minutes.
It has been demonstrated that a low-glycaemic index (GI) meal, more akin to one based on a normal, whole-food meal, as compared to highly refined processed carbohydrate foods (which typically have more rapid digestion and assimilation rates) result in lower respiratory exchange ratios and greater fat utilisation. Lower-GI pre-exertion meals result in a 59% longer time to exhaustion, faster performance times, and reduced rates of perceived exertion.4-6 It has similarly been demonstrated that a lower-carbohydrate meal of 30% CHO, 55% fat, and 15% protein is superior for enhancing endurance performance (time to exhaustion) than a high-carbohydrate meal of 71% CHO, 20% fat, and 9% protein.7
At low intensities < 70% of VO2max for relatively short periods (20-50 min), there is no significant effect on performance from lower- vs higher-glycaemic feedings but there is improved fat utilisation and reduced carbohydrate oxidation,8, 9 which provides a likely benefit to the preservation of glycogen, a finite fuel resource when compared to the relative abundance of fuel in adipose (fat) tissue. This has been further demonstrated in work by Achten and Jeukendrup. Both maximal fat oxidation and the intensity at which maximal fat utilisation was achieved, were reduced by the provision of 75 g of glucose in a graded exercise test.10 A systematic review of these effects concluded that a lower glucose load is superior to a higher glucose load pre-exercise.

Overall, for most athletes, especially recreational ones, gym goers, and bodybuilders, there is no benefit to performance from high-carb meals before training and events and there are likely to be reductions in fat-adaptation and fuel efficiency which could hinder longer term fat loss and impair metabolic health. A better option is to simply stick to a ‘carb-appropriate’ diet that provides sufficient fuel overall, sufficient protein and is nutrient-dense. Pre-workout meals featuring protein can provide some benefit to lean body mass and recovery and post-workout protein supplementation and possibly carbohydrate (depending on nutrition strategy, goals, and metabolic tolerance to carbohydrate) can also be of benefit.

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1.            Hargreaves M, Hawley JA, Jeukendrup A. Pre-exercise carbohydrate and fat ingestion: effects on metabolism and performance. Journal of Sports Sciences. 2004;22(1):31-8.
2.            Kuipers H, Fransen EJ, Keizer HA. Pre-Exercise Ingestion of Carbohydrate and Transient Hypoglycemia During Exercise. Int J Sports Med. 1999;20(04):227-31.
3.            Jeukendrup AE, Killer SC. The Myths Surrounding Pre-Exercise Carbohydrate Feeding. Annals of Nutrition and Metabolism. 2010;57(suppl 2)(Suppl. 2):18-25.
4.            DeMarco HM, Sucher KP, Cisar CJ, Butterfield GE. Pre-exercise carbohydrate meals: application of glycemic index. Medicine and Science in Sports and Exercise. 1999;31(1):164-70.
5.            Wong SHS, Siu PM, Lok A, Chen YJ, Morris J, Lam CW. Effect of the glycaemic index of pre-exercise carbohydrate meals on running performance. European Journal of Sport Science. 2008;8(1):23-33.
6.            Salarkia N, Azar KS, Taleban FA, Golestan B. The Effect of Pre-Exercise Carbohydrate Feeding with Different Glycemic Index on Endurance Exercise Capacity. Scientific Journal of Hamadan University of Medical Sciences. 2004;11(1):31-6.
7.            Murakami I, Sakuragi T, Uemura H, Menda H, Shindo M, Tanaka H. Significant Effect of a Pre-Exercise High-Fat Meal after a 3-Day High-Carbohydrate Diet on Endurance Performance. Nutrients. 2012;4(7).
8.            Sparks MJ, Selig SS, Febbraio MA. Pre-exercise carbohydrate ingestion: effect of the glycemic index on endurance exercise performance. Medicine and science in sports and exercise. 1998;30(6):844-9.
9.            Jentjens R, Cale C, Gutch C, Jeukendrup A. Effects of pre-exercise ingestion of differing amounts of carbohydrate on subsequent metabolism and cycling performance. European Journal of Applied Physiology. 2003;88(4):444-52.
10.         Achten J, Jeukendrup AE. The effect of pre-exercise carbohydrate feedings on the intensity that elicits maximal fat oxidation. Journal of Sports Sciences. 2003;21(12):1017-25.