Endurance Nutrition: Basic Principles and Strategies

Whether your focus is running, cycling or swimming, endurance training places unique stresses on your body.

One crucial factor is the way endurance training significantly increases daily energy requirements. There’s also increased requirements for key nutrients, minerals and vitamins.

In order to maximise exercise performance, enhance recover, and preserve immune health, it’s vital that we maintain a positive energy balance by replacing these key nutrients. We also need to maintain hydration levels both during and after exercise.

In this article we look at the basic principles of endurance nutrition. And the strategies employed by athletes to maximise performance and enhance recovery.

Endurance nutrition: increased calorie requirements

During endurance exercise, calorie expenditure rises significantly.

But it’s not just the calories you burn during exercise that need replacing. After exercise, your body goes through a process of repair and regeneration. And during this process, your metabolism remains elevated for several hours after exercise (depending on exercise intensity and duration).

How many extra calories do endurance athletes need?

This depends on several factors:

  • Training volume/duration — a greater volume or duration increases calorie expenditure
  • Training intensity — higher intensity = greater calorie expenditure (during and after exercise)
  • The type of sport — weight bearing sports like running burn more calories.
  • Your bodyweight — a greater bodyweight increases work rate and calorie expenditure.
  • Muscle mass — muscle is metabolically active so more muscle = more energy expenditure (during and after exercise)

If we use the example of an endurance runner who runs ~40 miles per week. They will burn approximately 4000 calories per week whilst training. We burn approximately 100 calories per mile when running, although this can vary between individuals (due to weight, muscle mass, exercise efficiency, etc.).

Based on this, we can ‘loosely’ calculate that they would need to consume an extra 4000 calories/week, or nearly 600 extra calories per day, to maintain muscle glycogen stores, body size, muscle mass and aid recovery between training sessions.

This is besides their normal recommended daily energy requirements (typically 2-2,500 calories day dependent on body mass, % body fat, gender etc).

The following formula provides an estimation of Basal metabolic rate (BMR):

  • Men: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5
  • Women: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161

Here, it’s necessary to remember that prolonged or intense exercise will significantly increase BMR. And as mentioned, this often remains elevated for several hours after exercise. So, it’s not always enough to calculate your BMR and add on the energy expenditure from exercise. 

Luckily, many gps watches and fitness trackers now do a good job of calculating daily energy expenditure. Making it a lot easier to calculate your daily energy requirements.

Energy requirements of elite endurance athletes

Among top level elite endurance athletes, the calorie requirements can jump significantly. And greatly exceed the normal recommended intakes for healthy adults.

As an example, an elite marathon runner with a running training volume of around 100miles/week, would require an average daily calorie intake of 3,500-4,000 calories — or more, depending on the intensity of the training sessions.

If we go one stage further and consider at an extreme endurance event like the Tour de France, calorie expenditure ramps up even more. Here calorie expenditure is so high that cyclists can consume around 6500 calories per day, with no increase in bodyweight!

Here, it’s not just about replacing calories spent during exercise; it’s also about repair and recovery of muscles and maintenance of bodyweight.

Endurance nutrition during competition and training

During endurance training and particularly when competing, it’s vital that you consume enough calories before, during, and after exercise:

  • If we consume too few calories before, or during exercise, then performance will suffer.
  • And if we don’t consume sufficient amounts after exercise, we compromise recovery.
  • This can have several negative effects, including reduced performance during training and racing, and increased risk of over-training and illness.

However, it’s not just about the quantity of calories for fuelling endurance sports. Attention needs to be placed on the ratio of key macronutrients (carbohydrates, fats, and proteins). In particular, carbohydrates have proven to have a significant role in exercise performance and post exercise recovery.

Primary energy sources during endurance exercise

The primary energy sources, during long distance events and training, are the aerobic metabolism of fats and carbohydrates.

At moderate exercise intensities (60 – 70% of VO2 max, 65 – 75% HR max), fat metabolism (as free fatty-acids) provide over 50% of your energy requirements. However, as exercise intensity increases, this proportion decreases; whilst the percentage of carbohydrate metabolism increases.

When exercise intensity approaches 80-85% VO2max (close to the intensity of the lactate threshold), carbohydrates become increasingly important, supplying more than half of our energy requirements.

It’s important to note that when exercise intensity increases, the total amount of energy supplied by fats doesn’t change — it’s the proportion that decreases due to increased carbohydrate metabolism. Besides the metabolism of carbohydrates and fats, there’s also a small amount of aerobic metabolism of proteins.

Carbohydrates for endurance exercise

Compared with bodily fat stores, we have comparatively small stores of carbohydrate (primarily stored as muscle and liver glycogen). And these can deplete rapidly:

  • Following 60 minutes of intense aerobic exercise, muscle and liver glycogen can decrease by around 50%
  • After 2 hours of exercise, our glycogen stores may deplete significantly
  • And the more intense the activity, the more quickly glycogen stores deplete

Since carbohydrates provide a large proportion of energy during moderate/intense physical activity; when stores become depleted, our fatigue levels increase and performance suffers.

One point to note: carbohydrates are involved in the complete metabolism of fats. So, when carbohydrate stores deplete, it also affects fat metabolism. An example is the point during a marathon where runners feel like they’ve hit a wall.

Taken together, this highlights the importance of maintaining carbohydrate stores before, during, and after exercise.

Carbohydrates before endurance races or training:

#1 Carbohydrates before races:

If you’ve got a big race coming up, then you’ll want to ensure muscle glycogen levels reserves are full. This is crucial in longer races like marathons, ultramarathons, and middle or long distance triathlons and duathlons.

Two strategies work well here:

  • You can increase your intake of carbohydrates over the final few days before key races.
  • Reduce training volume whilst maintaining your normal carbohydrate consumption.

It’s also important to consume a high carbohydrate meal, 3-4hours before competition; this helps to ensure glycogen levels remain full.

Read more about carbohydrate loading for endurance.

#2 Carbohydrates before training:

Whilst this is less important than when racing; low levels of muscle glycogen will impact training. So, if you’ve got an intense or prolonged session; then you’ll want to ensure that you don’t go into that session with depleted glycogen stores. Here, consuming carbohydrate a few hours prior to training can be beneficial.

Maintaining muscle glycogen levels is essential before more intense training sessions. And low levels will impact the quality of these sessions, and increase the stress placed on your immune system.

Another factor is maintaining glycogen stores by consuming enough carbs after training.

Carbohydrates after exercise

As I’ve mentioned, our carbohydrate stores are relatively small.

In order to maintain adequate levels, endurance athletes must regularly consume carbohydrates — especially after exercise.

The best strategies for maintaining muscle glycogen stores involve:

  • Consuming adequate amounts of carbohydrates after exercise — especially following intense or prolonged exercise.
  • Eating several small meals throughout the day (4-6 small meals).

Why consume several smaller meals?… Simply put, consuming smaller meals will help to ensure we use more carbohydrate to replace muscle and liver glycogen stores, and we store less as body fat.

Maintaining adequate levels of carbohydrate is important for post exercise recovery.

Read more about consuming carbohydrates after endurance exercise.

Carbohydrate during exercise

If you want to race to your full potential, then consuming carbs during exercise makes a massive difference.

This delays the point of muscle glycogen depletion; allowing you to race at higher intensities, and exercise for longer, before fatigue sets in. The most common approaches involve consuming energy gels, drinks or even energy bars or food like bananas during exercise.

One point to note here: if you’re going to use energy gels, or drinks, practice these in training first.

Not only will this allow you to test different gels, this will actually train your stomach to be more efficient at digesting gels during exercise. Interestingly, research has shown that consuming nutrition during training can improve race day performance.

I examine this in greater detail in this article: nutrition training for endurance runners.

Read more about carbohydrate during endurance exercise.

Fat metabolism and endurance exercise

As I mentioned earlier, fat metabolism provides a significant amount of our total energy needs, especially during low-moderate intensity exercise.

Unlike with carbohydrates, fat stores are not a limiting factor during exercise.

Even the leanest athletes will have more than sufficient fat reserves to fuel low intensity exercise for extended periods. In fact, just 1kg of body fat will provide enough energy to run around 3 marathons.

Endurance athletes don’t need to pay as much attention to the maintenance of bodily fat stores. That said, there is some evidence the consumption of a high fat meal prior to exercise (when muscle glycogen stores are already full) may benefit prolonged endurance exercise. This is due to increased levels of free fatty acids in the blood.

For health reasons, focus on consuming healthy fats:

  • Unprocessed vegetable oils (olive oil, sunflower oil, coconut, etc)
  • Avocado
  • Seeds rich in essential omega oils (pumpkin, sunflower, sesame, etc)
  • Oily fish (makeral, herring, sardines, etc)
  • Nuts (almonds, cashews, walnuts, Brazil nuts, peanuts)

Read more about fat intake for endurance athletes.

Training in a fasted state

In order to improve fat metabolism, some athletes deliberately train in a fasted state. This normally involves training early in the morning without breakfast. By doing this, athletes are training in a semi-fasted state.

Whilst we know that consuming carbohydrates before exercising can reduce the rate of fat metabolism, it’s not clear just how beneficial it is to train in a fasted state.

This training method is still controversial, particularly as it can lead to increased rates of muscle breakdown during exercise. It can also place greater levels of stress on the immune system. And if you choose to train in a fasted state, it’s vital that you maintain the required calorie intake. With this in mind, you must increase intake after exercise to balance the reduction in calorie intake (through fasting).

Low Carbohydrate Training Blocks

Another approach (which we’ll look at in a future article) is to employ a low-carbohydrate diet for specific blocks of training. This follows a similar theory to periodised training, i.e. specific nutritional approaches for certain blocks of training.

As an example, an athlete reduces their carbohydrate intake but maintains their total calorie intake by increasing the proportion of calories from fat and protein.

We believe this approach to benefit fat metabolism and may lead to reductions in body weight that may be helpful to endurance athletes.

Recent research in this area is promising, and we’ll cover this in a future article.

Protein metabolism and endurance exercise

Compared with fats and carbohydrates, the contribution of energy from protein metabolism is low during exercise, especially when less than 1 hour in duration (typically < 2%). However, as exercise duration increases, this can rise to ~ 5-10%, especially when glycogen stores become depleted.

Unlike fats and carbohydrate, our body does not store protein specifically for use during aerobic metabolism.

Most of the protein within our body is present within our muscles. In fact, your body comprises just over 40% muscle, with approximately 20% of this made up of protein.

There’s also a small amount of protein available as free amino acids. These amino acids are present in small amounts in your blood, with larger amounts within your muscles.

In order to metabolise protein, your muscle cells must either utilise the free amino acids that are circulating within your bloodstream, or breakdown muscle protein into amino acids.

In fact, we can metabolise the branched chain amino acids (BCAAs) and the amino acid alanine. This has led to the addition of BCAAs to energy drinks. This may benefit aerobic metabolism, spare muscle glycogen levels, and help to reduce the rates of muscle breakdown when exercising.

Reducing muscle protein breakdown

During prolonged endurance exercise (typically > 1hour), or when muscle glycogen levels become depleted, your body will start to breakdown muscle protein for use during aerobic metabolism. This can have a negative effect on strength, recovery and exercise performance.

With that in mind, there are two approaches that can help to reduce muscle breakdown:

  • Maintenance of muscle glycogen levels by consuming carbohydrates before, during, and after exercise
  • Consumption of protein (especially BCAAs or proteins high in BCAAs like whey protein) before, during and after exercise.

Whilst BCAAs can benefit endurance athletes by decreasing muscle damage and muscle breakdown; consuming too much during exercise can lead to an increase in ammonia production. Therefore, It’s important that intake of BCAAs is not excessive during exercise.


  • Daily energy expenditure significantly increases after endurance exercise.
  • Endurance athletes must ensure they consume adequate calories to match their daily requirements.
  • Particular attention needs to be placed on adequate carbohydrate consumption. This is vital for replenishing and maintaining muscle and liver glycogen stores, reducing muscle protein breakdown, improving exercise recovery and reducing the risk of illness.
  • Consuming carbohydrates before, and during competition, can improve endurance exercise performance.
  • Our body contains substantial stores of fat — even if you’re very lean — which we can metabolise during aerobic exercise.
  • Consuming a high fat meal prior to exercise may aid fat metabolism, providing that glycogen levels are maximal.
  • Protein metabolism also contributes a small amount of aerobic energy. This increases to around 5-10% during prolonged exercise, or when glycogen depletes.
  • Protein, and particularly BCAAs, can reduce muscle breakdown, enhance recovery and may aid muscle glycogen resynthesis.
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