Endurance refers to the component of exercise that enables performance over an extended time. Ultra-endurance encompasses training and events that are particularly long, with some disciplines lasting days or even weeks. A sport is usually considered to be ultra-endurance when it exceeds a timeframe of 2.5-4 hours. In the context of this article, we will be addressing nutrition recommendations for ultra-endurance exercise and how to maximise performance for training and competition.

Ultra-endurance refers to your body’s capacity to sustain exercise for a very long time period. It is mainly determined by the body’s ability to generate and utilise energy through multiple metabolic processes. Ultra-endurance is growing in popularity, with events that last hours, days, and even weeks becoming more common in the athletic and recreational fields.

Carbohydrates provide the primary source of energy when intense exercise duration lasts for greater than a few seconds and are extremely important for ultra-endurance activities. 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 ultra-endurance athletes consume between 8-12 grams of carbohydrates per kg of body weight per day ^[3].

The timing of carbohydrate ingestion can also play an essential 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. Their consumption can provide a fuel source for the muscle as glycogen stores are depleted ^[3]. This is especially important during ultra-endurance activities. The long duration of these events makes replenishing energy stores critical for success. It is generally recommended that during exercise bouts of >2.5 hours, athletes consume between 60 and 90 grams of carbohydrates per hour. Although carbohydrate uptake mechanisms are usually limited to 60 grams per hour, ultra-endurance athletes may benefit from ingesting “multiple transport carbohydrates”, which contain different sugar types (e.g. fructose and glucose) ^[4]. These carbohydrates are utilised faster, as two transport mechanisms are used by the cells during digestion.

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 ultra-endurance athletes as extended durations of intense exercise will damage muscle fibres and other tissues in the body. An adequate amount of protein in the diet will maximise recovery and drive training adaptation ^[4].

It is generally recommended that endurance athletes consume 1.5-1.8 grams of protein per kilogram of body weight per day ^[5]. Despite this, it is worth noting that many ultra-endurance athletes self-select protein levels of 2-2.5 g/kg/day ^[5].

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 ^[6]. To maximise this response, it is also recommended that protein is consumed every 3-4 hours, with around 20g being ingested soon after exercise ^[4],^[7]. This means that protein intake should also be included during events, especially those lasting multiple days.

During ultra-endurance exercise, carbohydrates usually 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]. Additionally, when exercise intensity is lower, fatty acids are utilised more for energy production ^[8]. Some ultra-endurance activities may demand fat utilisation as a predominant energy source, as their duration forces lower exercise intensity.

Fatty acids are also crucial in ultra-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) ^[9]. 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 ^[2]. Daily fat requirements are estimated at 2 grams per kilogram of body weight per day to replenish triacylglyceride stores after prolonged endurance training ^[2].

As an ultra-endurance athlete, providing your body with the micronutrients it needs to optimise metabolic function is essential. 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 ^[10]. 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 body ^[4]. Therefore, an iron deficiency can decrease 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 ultra-endurance athletes, as oxidative stress on the muscles and other cells is increased with exercise duration and the body’s relevant demand for oxygen ^[6]. 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 ultra-endurance athlete will face during competition, with an incidence rate of 60-96% ^[5]. 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 ^[11]. The most commonly reported symptoms include dizziness, nausea, stomach or intestinal cramps, vomiting, and diarrhoea ^[1].

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 ^[4]. The potential of prebiotics to exert an anti-inflammatory effect has been identified as particularly relevant to ultra-endurance athletes due to the prevalence of increased gut permeability and inflammation ^[4].

Having a diet high in prebiotic fibres will also 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 ^[4]. Optimising metabolic function will result in greater energy production for endurance capacity, whilst a more robust immune system helps to prevent illness. Therefore, 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 ^[4].

Hydration is one of the fundamental components of success in ultra-endurance exercise. Around 70% of the body’s overall mass is comprised of water, so maintaining optimal levels of hydration is critical for metabolic function ^[12]. Performance can be significantly impaired when just 2% of body weight is lost through sweat ^[6]. Due to the long durations of ultra-endurance events, maintaining a hydrated state is of utmost importance.

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 ^[12].

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 ^[12]. 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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