Key Points
- There is little difference for fat or weight-loss between fasted and fed training.
- Carbohydrate-containing meals taken before training are typically unnecessary for sessions lasting less than 90 minutes.
- For longer sessions or when the overall volume of high-intensity sessions per week is high, carb-containing meals before training can benefit performance.
- Wholefood (lower-GI/GL) pre-training meals are likely to be superior to fast-digesting carb meals.
There is an ongoing debate between proponents of training fasted to increase the use of fat-for-fuel and those who support (typically high-carbohydrate) meals before training to supply additional fuel for higher-intensity intra-session bouts of activity. Fasted training increases fatty acid utilisation acutely, and this has led to it being a ‘go-to’ method for fat-loss and body-composition goals but a 2017 review of the evidence has shown that there is little difference in overall energy expenditure, fat loss, or weight loss between fed and fasted training.1
There is little difference in overall energy expenditure, fat loss, or weight loss between fed and fasted training
Should I have some carbs before training?
Carbohydrate ingestion before exertion is associated with improvements in performance for bouts of intensive activity greater than 90 min but it also reduces lipolysis (the breakdown of fat for fuel) and can lead to hypoglycaemia which can negatively affect performance in some individuals.2-4 It’s also generally unnecessary for bouts of exercise under 90 minutes.
Carbohydrate ingestion before exertion is associated with improvements in performance for bouts of intensive activity greater than 90 min
If you are having carbs before training, either because you feel better when performing, and/or you are competing or training in an event or session longer than 90 minutes, having slower-digesting, whole-food based meals are superior to fast-digesting sugary drinks or snacks. It has been demonstrated 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 (i.e., more fat used for fuel compared to ‘burning’ sugar) and greater fat utilisation. Lower-GI pre-exertion meals also resulted in a 59% longer time to exhaustion, faster performance times, and reduced rates of perceived exertion.5-7 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.8
Slower-digesting, whole-food based meals are superior to fast-digesting sugary drinks or snacks
At low exercise intensities (< 70% of VO2max) for relatively short periods (20-50 min), there is no significant effect on performance from lower- vs higher-carb feedings but there is improved fat utilisation and reduced carbohydrate oxidation resulting from a low-carb meal, 9, 10 which provides a likely benefit for the preservation of glycogen which is a finite fuel resource when compared to the relative abundance of fuel in 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.11 A systematic review of these effects concluded that a lower glucose load is superior to a higher glucose load pre-exercise.
For most athletes, especially recreational ones, gym-goers, and bodybuilders, there is no benefit to performance from specific high-carb pre-training or pre-event meals but on the other hand, there’s not likely to be any significant difference in fat loss or health outcomes if you do have a meal before training.
For most athletes there is no benefit to performance from specific high-carb pre-training meals
Remember that lower-carbohydrate athletes can store similar amounts of glycogen and restore it at the same rate as higher-carb consuming athletes,12 BUT… ALL athletes can suffer glycogen depletion if they are exercising for longer than 90 minutes at a time or have a high frequency of long-duration, high-intensity bouts of exercise. So, whether you prefer a low- or high-carb approach, carb-intake relative to your preferred diet type will still need to be higher if you are at risk of glycogen depletion. However, for lower-carb athletes, a better option than a pre-exercise carb-containing meal might be to take additional carbohydrate during activity to benefit from non-insulin mediated glucose uptake that is independent of benevolent Pseudodiabetes (sorry about the nerdy stuff – check out the article here). Notwithstanding endurance athletes, whether low- or high-carb, often benefit from intra-event carbohydrate supplementation.
What should I do to maximise performance?
The best advice is to do what feels best. If you thrive on training fasted (which is often the case for athletes and everyday Joes and Johannas training first thing upon rising) then keep doing that. However, if you think you might feel better or have better performances eating a meal before training or events, then give it a crack (and vice versa). If you are eating a meal before training, the best option is likely to be a ‘carb-appropriate’ meal based on whole foods.
For events and training bouts longer than 90 minutes, you are likely to benefit from pre-training meals containing higher levels of carbohydrate, especially if your overall carbohydrate intake is not sufficient to meet your carbohydrate requirements for higher-intensity (glycolytic or ‘sugar-burning’) activities.
References
1. Hackett D, Hagstrom AD. Effect of Overnight Fasted Exercise on Weight Loss and Body Composition: A Systematic Review and Meta-Analysis. Journal of Functional Morphology and Kinesiology. 2017;2(4):43.
2. 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.
3. 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.
4. Jeukendrup AE, Killer SC. The Myths Surrounding Pre-Exercise Carbohydrate Feeding. Annals of Nutrition and Metabolism. 2010;57(suppl 2)(Suppl. 2):18-25.
5. 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.
6. 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.
7. 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.
8. 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).
9. 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.
10. 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.
11. 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.
12. Volek JS, Freidenreich DJ, Saenz C, Kunces LJ, Creighton BC, Bartley JM, et al. Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism. 2016;65(3):100-10.
