Endurance refers to the component of exercise that enables performance over an extended time. A sporting discipline is usually considered to be endurance when it exceeds a timeframe of 30 minutes to one hour. However, these timeframes can vary from an hour or two right up to multi-day events (ultra-endurance). In the context of this article, we will be addressing nutrition recommendations for endurance exercise as it relates to events of 1-2.5 hours.

Endurance refers to your body’s capacity to sustain exercise for an extended period. It is determined largely by the ability to distribute oxygen around the body and utilise it for energy production within the muscles. Many sporting disciplines require an endurance component, and in many cases, it is the key determinant for success.

Carbohydrates are the most important macronutrient for the performance of endurance athletes. They provide the main source of energy when exercise duration lasts for greater than a few seconds. Stored muscle glycogen and blood glucose are the most important substrates for contracting muscle (both of which are maintained through the consumption of carbohydrates) ^[1]. Low glycogen concentrations lead to reduced high-intensity performance and less time to fatigue ^[2]. To maintain these energy stores, it is recommended that endurance athletes consume between 6-12 grams of carbohydrates per kg of body weight, per day, preferably from quality sources such as whole grains, vegetables, and fruits ^[3], ^[4].

The timing of carbohydrate ingestion can also play an important role during endurance exercise itself. For example, it is recommended that athletes consume 1-4 grams of carbohydrates per kg of bodyweight, 1-4 hours before competition to ensure glycogen stores are full ^[3]. This helps to ensure that energy stores last as long as possible before reaching fatigue.

Carbohydrates can also be utilised within exercise itself. This is because their consumption can provide a fuel source for the muscle as glycogen stores are depleted ^[3]. It is generally recommended that during exercise bouts of 1-2.5 hours, athletes consume between 30-60 grams of carbohydrates per hour, as uptake is limited to around one gram per minute by cellular digestive and transport systems ^[3].

Finally, post-exercise, it is recommended that you ingest 1-1.2 grams of carbohydrates per kg of body weight to optimise muscle glycogen resynthesis. This reduces fatigue and allows the body to recover for the next session. Prolonged depletion of carbohydrates can impair immune function, reduce training output, and cause burnout ^[2].

Consuming high levels of protein will provide the nutrients your body needs to build and repair muscle tissue. This is crucial for endurance athletes as extended durations of intense exercise will damage muscle fibres. An adequate amount of protein in the diet will maximise recovery and drive training adaptation ^[5].

It is generally recommended that endurance athletes consume 1.5-1.8 grams of protein per kilogram of body weight per day ^[6]. As well as being sufficient in protein, a well-balanced diet should provide an adequate combination of amino acids to match the demand for metabolic pathways and protein synthesis. Rapidly digested proteins containing high levels of essential amino acids and adequate leucine are most effective at stimulating muscle protein synthesis ^[4]. To maximise this response, it is also recommended that protein is consumed every 3-4 hours, with around 20g being ingested soon after exercise ^[5], ^[7].

During endurance exercise, carbohydrates provide the main energy source for the muscles. However, fats also play a role in supplementing energy production. Fats can be stored in the muscle as triacylglyceride, which serves a similar purpose to glycogen. This is a viable fuel source for energy production that supplements carbohydrate metabolism ^[2].

Fatty acids are also important in endurance athletes’ diets due to their role in other cellular processes. They are required to aid the absorption of fat-soluble vitamins, many of which play an important part in energy production. They also provide the raw material for the synthesis of hormones that drive the response to training (such as muscle growth and repair) ^[8]. Additionally, fatty acids are required to maintain nerve cells, as they make up a protective layer called the myelin sheath ^[2]. This is vital for such athletes as continual muscle function relies heavily on repeated neural firing.

It is generally recommended that around 30% of an athlete’s daily energy intake comes from fat sources, whilst up to 50% may be appropriate under vigorous training conditions ^[4].

As an endurance athlete, it is essential to provide your body with the micronutrients it needs to optimise metabolic function. Any deficiencies could result in the body prioritising short-term survival mechanisms and placing less priority on those that enhance long term health and performance ^[9]. For this reason, it is essential to address micronutrient intake across a broad spectrum of vitamins and minerals.

There are also specific micronutrients that play more immediate roles in optimal endurance performance. For example, iron, folate, and vitamin B12 are all fundamental elements for red blood cells, which are responsible for delivering oxygen throughout the body5v. Therefore, an iron deficiency can result in decreased exercise performance as the muscle cannot effectively utilise oxygen for energy production.

Additionally, vitamins C, E, and K play antioxidant roles in the body, removing harmful free radicals. This is particularly relevant to endurance athletes, as oxidative stress on the muscles and other cells is increased with exercise duration and the body’s relevant demand for oxygen ^[4]. Reducing this oxidative stress can help improve recovery and is beneficial for overall health and metabolic function.

Gastrointestinal discomfort is one of the most common issues an endurance athlete will face during competition. When you undergo intense exercise, the rate of blood flow increases around the body to demanding organs such as the skeletal muscles. As a result, the digestive system may experience inadequate blood flow, as other organs are prioritised. This can lead to inflammation and irritation of the gastrointestinal tract ^[10].

If the gut microbiome is healthy, it will optimise systems that prevent this inflammation, reducing discomfort and allowing you to perform without interruption. This can be achieved by including an appropriate array of prebiotics in your diet, a type of fibre that acts as food for the microbiome. Prebiotic substances can help to increase the abundance of healthy bacteria in the gut and reduce gastrointestinal issues during endurance exercise ^[5].

Having a diet high in prebiotic fibres will provide the nutrients that gut bacteria need to produce beneficial metabolic by-products, called postbiotics. These postbiotic substances help to modulate many aspects of the host metabolism and immune system ^[5]. Optimising metabolic function will result in greater energy production for endurance capacity, whilst a more robust immune system helps to prevent illness. The effects of a healthy gut microbiome on endurance performance can also be attributed to the indirect maintenance of good health and subsequently, the ability to optimally train and compete ^[5].

Hydration is one of the fundamental components of success when it comes to endurance exercise. Around 70% of the body’s overall mass is comprised of water, so maintaining optimal levels of hydration is key for metabolic function ^[11]. Performance can be significantly impaired when just 2% of body weight is lost through sweat ^[4].

Hydration can be a challenging aspect to manage, as it is possible to both under-hydrate and over-hydrate. It is also difficult to know precisely how much water to drink during different scenarios, as sweat rate and your body’s demands may change due to individual factors, environment, exercise duration, and exercise intensity ^[11].

In general, good hydration practices include starting exercise in a hydrated state, taking caution not to overhydrate, and replacing fluids lost during exercise through sweating ^[11]. As a guide, average sweat rates during exercise are reported to be between 0.5 and 2L per hour. Consequently, water intake should match these rates to offset weight loss through fluids.

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