Whether the goal is a triathlon, an Ironman, or a recreational endurance event, nutrition planning is a core determinant of performance. Bringing the fuelling strategy to the same level of preparation as the training programme produces measurable gains.
This article covers the macronutrients; protein, carbohydrate, fat and hydration. Each is addressed below.
Protein
Protein supplies the building blocks for all tissues and organs in the body. It contributes to maintaining and increasing muscle mass[1] and to strengthening tendons and bone[2]. In the context of endurance exercise, protein supports the muscles in oxidising carbohydrates and fats[3], [4].
Many athletes consume most of their protein at the evening meal, which is not optimal for recovery[5]. Protein delivered shortly after training delivers the recovery benefits more reliably. Post-exercise protein supports muscle recovery[6] by reducing exercise-induced muscle damage[7], [8] and the perception of muscle soreness[9].
Carbohydrate
Carbohydrate intake before and during exercise supports endurance performance across short and long durations[10]. For sessions of 2.5 hours or longer, recommended intake is around 1.2 g of carbohydrate per kg of body mass per hour to maintain performance[11]. This intake also delays glycogen depletion[12]. Glycogen is the substrate athletes need to restore after hard training; combining protein with carbohydrate during recovery supports optimal glycogen replenishment[13]. Recent studies indicate that lactose and its components — galactose and glucose — function as useable and efficient energy sources during endurance exercise compared with supplementation with glucose alone or with fructose[14]. This points to an under-explored role for lactose in sports nutrition alongside established carbohydrate supplements.
Carb Guidelines
Fats
Endurance sessions can require energy that exceeds available carbohydrate stores, making the ability to use body fat as fuel relevant[15]. To target fat utilisation during a session, training can begin with a low carbohydrate level — for example by avoiding carbohydrate intake beforehand[16].
Hydration
Fluid requirements depend on training conditions. Hot or humid conditions raise demand. Rehydration is also needed during and after exercise.
Fluids combined with electrolytes — sodium, potassium, and magnesium — support hydration. Adding protein to the fluid–electrolyte mix has been shown to rehydrate athletes more effectively than water and electrolytes alone[17].
Fuelling strategy, like training, requires refinement in the lead-up to a target event. Testing the strategy well in advance allows for adjustment before performance day.
[1]EFSA Journal 2010;8(10):1811, 2011;9(6)2203, Cermak et al. 2012
[2]EFSA Journal 2010;8(10):1811, 2011;9(6)2203, Rizzoli et al. 2018
[3]Hansen et al. 2020 https://doi.org/10.1186/s12970-020-00376-3
[4]Rowlands et al. 2011 https://doi.org/10.1152/physiolgenomics.00073.2011
[5]Gillen et al. 2016 https://doi.org/10.1123/ijsnem.2016-0154
[6]Cintineo et al. 2018 https://doi.org/10.3389/fnut.2018.00083
[7]Hansen et al. 2015 https://doi.org/10.1123/ijsnem.2014-0083
[8]Brown et al. 2018 https://doi.org/10.1139/apnm-2017-0412
[9]Jäger et al. 2018 https://doi.org/10.1186/s12970-017-0177-8
[10]Stellingwerff and Cox 2014 https://doi.org/10.1139/apnm-2014-0027
[11]https://researchonline.ljmu.ac.uk/id/eprint/18221/8/Fuelling%20the%20female%20athlete%20carbohydrate%20and%20protein%20recommendations.pdf
[12]Beelen et al. 2010 https://doi.org/10.1123/ijsnem.20.6.515
[13]Thomas, Erdman et al. 2016 https://doi.org/10.1249/mss.0000000000000852
[14]Odell, O. J., Impey, S. G., Shad, B. J., Podlogar, T., Salgueiro, R. B., Rowlands, D. S., & Wallis, G. A. (2022). Oxidation of independent and combined ingested galactose and glucose, during exercise. J Appl Physiol (1985). https://doi.org/10.1152/japplphysiol.00105.2022 Odell, O. J., Podlogar, T., & Wallis, G. A. (2020). Comparable Exogenous Carbohydrate Oxidation from Lactose or Sucrose during Exercise. Med Sci Sports Exerc, 52(12), 2663-2672. https://doi.org/10.1249/MSS.0000000000002426
[15]Maunder et al. 2018 https://doi.org/10.3389/fphys.2018.00599
[16]Impey et al. 2018 https://doi.org/10.1007/s40279-018-0867-7
[17]Li et al. 2018 (http://dx.doi.org/10.1080/17461391.2018.1442499), EFSA Journal 2011;9(6):2211