Nutritional Best Practices for Endurance Athletes

The Speed Read: Why Nutrition Matters

Fuelling for endurance isn’t just about loading up on carbs the night before a race. To perform, recover, and stay healthy, you need a well-rounded nutritional strategy that covers carbohydrates, proteins, fats, fluids, and micronutrients. This guide blends evidence from scientific literature with my real-world experience from hundreds of long sessions (and too many mistakes!), helping you avoid mid-race crashes and recover day after day.

Building the Foundation: Why Nutrition Matters

Macronutrients (carbohydrates, proteins, fats), hydration, and micronutrients are critical for sustaining energy, supporting muscle repair, and maintaining health. Whether you're training for your first marathon or trying to beat your mates on the Saturday group ride (my current goal), getting these pillars right can make all the difference (Thomas et al., 2016).

Carbohydrate Intake

Daily Requirements

Carbohydrates are the primary fuel for endurance efforts, powering glycolysis and glycogen stores. I derived most of my dietary carbs from a well-rounded diet, avoiding sugary snacks even when cravings hit (most of the time). Research recommends 6–10 g/kg body weight/day, increasing to 8–12 g/kg during hefty training blocks or multi-day events (Burke et al., 2011). The timing of carbohydrate intake can be key and very individual. For me, too many carbohydrates in the morning seem to lead straight to a hypoglycemic rebound, leaving me feeling flat.

Pre-Exercise Nutrition

To maximise glycogen stores, consume a carb-rich meal 1–4 hours pre-exercise, targeting 1–4 g/kg body weight (Burke et al., 2011). Most people can eat much closer to the start of a bike effort than a running race. Find out what works for you. My pre-race favourite was tins of rice pudding! Some people find reducing fibre in their pre-race diet reduces the chances of stomach problems, and others don’t have a problem. Opting for low-fibre or no-fibre choices is a safe bet to avoid sluggishness and stomach problems.

During Exercise

For sessions exceeding 90 minutes, consume 60 plus g/h of carbohydrates, up to 120 g/h for intense efforts and ultra-endurance events, using gels or sports drinks. Combining glucose and fructose (e.g., 1:1 ratio) enhances absorption (Burke et al., 2011). If you’ve ever bonked in training, you’ll know why mid-session fuelling is critical!

Post-Exercise Recovery

Post-exercise, aim for 1–1.2 g/kg body weight of carbohydrates within 30 minutes to replenish glycogen, ideally paired with 0.2–0.4 g/kg protein (Thomas et al., 2016). This window is when muscles are most receptive to recovery.

Protein Intake

Protein supports muscle repair and adaptation. I aim for 1.2–2.0 g/kg body weight/day, mostly from milk, eggs, and meat, though tofu and lentils work too. Research supports this range for endurance athletes, with higher needs during intense training (Tipton & Wolfe, 2004). Post-workout, I include 10–20 g of protein within 30 minutes, especially after hard runs with high eccentric load.

Fat Intake

Fats are crucial for longer efforts, hormone balance, and absorbing fat-soluble vitamins. Aim for 20–35% of daily energy from quality sources like olive oil, fatty fish, nuts, and seeds (Thomas et al., 2016). Avoid high-fat meals pre-exercise—they’re slow to digest and can upset your stomach mid-session.

Hydration and Electrolytes

Fluid Intake

Hydration regulates core temperature and effort. I sip fluids regularly and monitor sweat loss by weighing myself before and after long sessions. Aim to keep weight loss <2% during exercise (Sawka et al., 2007).

Electrolyte Replacement

Sweat depletes sodium, potassium, magnesium, and chloride. I target ~1 g salt (400 mg sodium)/L of fluid during long sessions, especially in heat, adjusting for my salty sweat (Maughan & Shirreffs, 2010). For short sessions or training in the cool, you probably don’t need to worry about electrolyte replacement. For long and intense efforts, in hot conditions, my experience is that you need to intake sodium to prevent muscle cramps. Think carefully about how many electrolytes you are ingesting anytime you are consuming significant amounts of fluid (> 1L per hour) to replace your sweat loss. Sports drinks or electrolyte tablets help.

Post-Exercise Rehydration

Post-session, drink 1–1.5 L fluid/kg body weight lost, adding salt (100–1400 mg/L) for retention (Sawka et al., 2007). I use salty foods like broth or pretzels alongside recovery drinks.

Micronutrients

Vitamin D (bone health), iron (oxygen delivery), and vitamin C (immune function) are key. A colourful, whole-food diet usually covers needs, but if I feel run down, I get bloodwork or supplements under professional guidance (Holick & Chen, 2008). Supplement to your individual needs. I always have low Vitamin D levels, so make sure to take extra during the winter.

Nutrient Timing

Before Exercise

I keep pre-exercise meals simple: moderate carbs, low fibre, small protein, minimal fat. Think toast, rice cakes with jam, or banana (Burke et al., 2011). The goal is digestible fuel, not a gut bomb.

During Exercise

I start fuelling within 45 minutes, even if not hungry, using small, regular carb doses (gels, drinks) and electrolyte fluids to maintain energy (Burke et al., 2011).

After Exercise

Within 30 minutes post-exercise, I target a 3:1 or 4:1 carb-to-protein ratio (e.g., smoothie with oats and whey, rice and eggs, or recovery drink with banana) (Thomas et al., 2016). Timing matters—delay it, and recovery slows.

Recognising Poor Nutrition

I’ve learned the hard way that nutritional gaps derail performance. Signs include:

• Running: Legs feel like concrete, heart rate spikes, you can’t focus on anything or you’re irrationally angry at a gel packet (or anything really!)
• Cycling: Can’t hold wattage, hands tingle from electrolyte loss, or you start cold-sweating. I get extremely painful quads.
• Swimming: Losing feel for the water, form breaks, or you miscount laps.

Mental fog, irritability, or sluggish reflexes signal fuelling issues.

Final Thoughts

Nutrition isn’t about perfection—it’s about consistency. Tune into your body, prioritise carbs, protein, quality fats, hydration, and micronutrients like vitamin D and iron. Get it right, and you’ll feel stronger in training and racing.

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References

• Burke, L. M., Hawley, J. A., Wong, S. H. S., & Jeukendrup, A. E. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(sup1), S17–S27. https://doi.org/10.1080/02640414.2011.585473
• Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528. https://doi.org/10.1016/j.jand.2015.12.006
• Sawka, M. N., Burke, L. M., Eichner, E. R., Maughan, R. J., Montain, S. J., & Stachenfeld, N. S. (2007). American College of Sports Medicine position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377–390. https://doi.org/10.1249/mss.0b013e31802ca597
• Tipton, K. D., & Wolfe, R. R. (2004). Protein and amino acids for athletes. Journal of Sports Sciences, 22(1), 65–79. https://doi.org/10.1080/0264041031000140554
• Maughan, R. J., & Shirreffs, S. M. (2010). Development of individual hydration strategies for athletes. International Journal of Sport Nutrition and Exercise Metabolism, 20(5), 377–384. https://doi.org/10.1123/ijsnem.20.5.377
• Holick, M. F., & Chen, T. C. (2008). Vitamin D deficiency: A worldwide problem with health consequences. The American Journal of Clinical Nutrition, 87(4), 1080S–1086S. https://doi.org/10.1093/ajcn/87.4.1080S

About the Author

Alistair Brownlee is a two-time Olympic gold medallist, Ironman Champion, and co-founder of Truefuels. He is driven by a belief in science-backed training, clear structure, and removing friction from performance.