Sports nutrition for endurance athletes: the complete beginner's guide

Sports nutrition can quickly sound complicated: macros, gels, timing, supplements. But for most endurance athletes the biggest gains do not come from expensive powders. They come from the basics: eating enough, on time, and matched to your training.

Nutrition also does not have to be a strict diet. It is a tool to train harder, recover faster, and toe the start line fitter. This is the complete beginner's guide to sports nutrition for endurance athletes.

Carbohydrates: your main fuel

For endurance sport, carbohydrates are the main energy source, especially at higher intensity. Your stores in the muscles and liver (glycogen) are limited, and when they run out you hit the well-known wall. Anyone who consistently eats too few carbs often trains on an empty tank: heavy legs, lower quality, slower recovery.

The modern approach is to let your intake scale with your load, in grams per kilo of body weight:

• Easy day: about 3 to 5 g/kg
• Moderate day (about 1 hour of training): 5 to 7 g/kg
• Hard day (1 to 3 hours of endurance training): 6 to 10 g/kg

For a 70-kilo athlete that works out to roughly 350 to 700 grams of carbohydrate a day, depending on what is on the programme that day. Your fuel follows your training, not the other way around. More around your hard and long days, a bit less on easy days.

Protein: the building blocks for recovery

Protein is needed for recovery and adaptation, not only for building muscle but also for making the enzymes and mitochondria that carry your endurance. Endurance athletes need more of it than non-athletes.

A workable guideline is 1.4 to 1.8 grams per kilo of body weight per day. More important than the exact number is the spread: divide your protein across the day in portions of about 20 to 40 grams, every three to four hours. That works better for your recovery than cramming it all into one big evening meal.

Eating during training

Whether you need to refuel during exercise depends mainly on the duration:

• Shorter than an hour: nothing needed, water is enough.
• One to two and a half hours: 30 to 60 grams of carbohydrate per hour.
• Longer than two and a half hours: up to 90 grams per hour, but only with a mix of carbohydrates.

Why the mix? Your gut can only absorb one type of sugar (such as glucose) up to about 60 grams per hour, there is a transport limit. By combining glucose with fructose you use a second absorption route and your gut can process more, up to around 90 grams per hour. That is the classic 2-to-1 ratio.

For reference: an energy gel contains about 20 to 30 grams of carbohydrate, a bottle of sports drink around 30 to 40 grams. So "30 to 60 grams per hour" works out to roughly one gel every 30 to 45 minutes, or a bottle plus a gel.

The very highest intakes (90 to 120 grams per hour) you see in elite marathoners and Ironman athletes are for very well-trained, "gut-trained" athletes. Not a starting point for the average endurance athlete.

Fluid and salt

The goal is to limit dehydration without overdoing it. Both extremes do harm: too much fluid loss hurts your performance, but drinking far more than you lose brings a risk of a dangerously low sodium level.

In practice:

• Drink to thirst as the basic rule for most sessions.
• Try to keep your weight loss over a session under 2 percent of your body weight. Gaining weight during exercise is precisely the sign that you are drinking too much.
• Test yourself: weigh yourself before and after a long session. Every kilo lost equals about a litre of sweat. That personalises your fluid needs better than any general rule, because sweat loss varies hugely from person to person.
• Salt becomes important on longer or hot efforts and for salty sweaters. A sports drink usually delivers 0.5 to 0.7 grams of sodium per litre; that can be higher for those who sweat a lot and saltily.

Timing: before, during, and after

Before training. A carbohydrate-rich meal of 1 to 4 grams per kilo, 1 to 4 hours beforehand, low in fat and fibre. The bigger the meal, the more time you leave for it. A small extra snack in the last hour can help for longer efforts.

During training. See above: from about an hour onwards, your intake becomes relevant.

After training. Combine carbohydrates and protein, and drink enough. The stubborn idea of a strict "thirty-minute window" is outdated: the period in which your body recovers well is much broader, and your total intake across the day weighs more than the exact timing. A normal, balanced meal within a few hours is enough. Only when you do two training sessions close together does fast refuelling really matter.

Race nutrition and training your gut

The golden rule for every race: nothing new on the day itself. No unknown gel, drink, brand, or amount tried out for the first time in competition. You practise everything beforehand in training.

For longer races you build up your nutrition in phases:

• Carb loading (only for long events, from about 90 minutes): in the days beforehand you raise your carbohydrate intake significantly, spread across several meals rather than one giant plate of pasta.
• The pre-race meal: carbohydrate-rich, 1 to 4 hours beforehand.
• During: execute your practised plan.

And your gut is trainable. By practising your nutrition plan a few times during long sessions in the final weeks, and building your intake up gradually, it gets used to a higher load. That is exactly what makes those higher intakes of 60 to 90 grams per hour possible without stomach and gut trouble.

And "train low"?

You sometimes hear about "train low": deliberately doing a few easy sessions with little available carbohydrate (such as a fasted morning run) to boost certain adaptations. That gives interesting signals at the cellular level, but honesty demands: for actual race performance in well-trained athletes it is not proven to be better than simply fuelling well. And eating chronically low-carb or ketogenic can actually harm your high-intensity performance. See it as an optional, advanced technique for easy sessions, not as a diet. You always fuel your hard days and races well.

Supplements that actually work

First this: 80 percent of your result comes from normal, balanced nutrition, training, and sleep. Supplements are a small final layer. But a few do have strong evidence for endurance sport:

• Caffeine lowers your perceived effort and improves your endurance. One of the best-supported aids. Usually 3 to 6 mg per kilo, about 30 to 60 minutes beforehand.
• Beetroot juice (nitrate) improves your exercise economy: you use less oxygen at the same pace. The effect is clearer in less-trained athletes than in top athletes.
• Creatine is best known for strength, but it helps endurance athletes with short, explosive efforts like surges and hills, and it supports your strength training. Bear in mind a little extra water weight.

Caffeine and beetroot juice are the two that pay off most for the average endurance athlete. Always start with your food, not with the supplement jar.

No quick fix, but lasting habits

The biggest mistake in sports nutrition is thinking in diets and bans. What works are lasting habits that evolve with your life and your season: a healthy base, matched to your training, with room to enjoy yourself.

Want to really dial this in for your situation and goals? Our nutrition coaching for athletes in Antwerp translates these guidelines into a tailored plan, whether you want to get fitter or work towards a specific race. Start with a free intro call. Good nutrition will not make you faster on its own, but it does make sure all your training pays off.