Nutrition for Endurance Sports

Ideally, the last large meal should be eaten 2-4 hours before exercise. The following applies: the more intense the upcoming exercise, the higher the carbohydrate content of the meal should be. In the case of moderate endurance exercise, the proportion of proteins and fats can be somewhat higher, but a greater time gap should then be maintained before the activity. If it has been a long time since your last meal, an easily digestible snack is recommended before training

Carbohydrate intake during exercise prolongs performance by preserving muscle glycogen reserves, maintaining liver glycogen stores (important for supplying energy to the brain), preventing hypoglycemia and maintaining a high energy flow. A limiting factor during submaximal exercise is not so much the gastric emptying rate or the absorption capacity of the skeletal muscles, but rather absorption in the small intestine. Protein intake during exercise can reduce the release of muscle enzymes such as creatine kinase and reduce muscle fatigue. However, protein intake during exercise does not appear to have any significant benefit for training success per se. The recommended hourly intake of carbohydrates varies greatly and should be adjusted individually. On average, around 0.7 g of carbohydrates per kilogram of body weight per hour is a guideline for moderate endurance exercise. For more intensive exercise, this amount can be doubled.

During training, we set physiological stimuli that trigger numerous adaptationprocesses in the body and ultimately increase our performance. However, without the provision of the necessary nutrients, we block the signaling pathways that enable these adaptations. Studies show that a timely supply of nutrients not only supports these processes, but also improves the training effect. It is particularly beneficial to consume proteins from different sources in combination with carbohydrates. Branched-chain amino acids in combination with the insulin release triggered by carbohydrates optimally stimulate protein synthesis and the associated mTOR signaling cascade. In addition, we lose considerable amounts of fluid and minerals through thermoregulation and sweating during exercise. These losses can only be partially compensated for during activity, which is why rehydration after training is essential. It is therefore advisable to consume a mixture of carbohydrates, proteins, amino acids and minerals, ideally in liquid form, within 30 to 120 minutes after exercise. The next meal or a small snack should also be planned for this period.

Before the competition, it is particularly important to focus on easily digestible carbohydrates. To avoid stomach problems, dishes high in fat and fiber should be avoided. The following rule also applies: No experiments! Only eat foods that you are used to and that your body tolerates well.

Around 3-4 hours before the start, it is advisable to consume around 4-5 g of carbohydrates per kilogram of body weight. Ideal options are dishes such as porridge with banana, rice with vegetables or pasta with a lean sauce. These meals provide the necessary energy without putting unnecessary strain on the stomach.
Shortly before the race, about 1-2 hours before the start, a small snack can help to keep blood sugar levels stable. Around 1-2 g of carbohydrates per kilogram of body weight is sufficient here. Good snacks in this phase are, for example, white bread with honey, a banana or a granola bar. These foods provide quickly available energy without being heavy on the stomach. Fluid intake is also a decisive factor. It is important to drink enough before the race to ensure you are well hydrated at the start. Isotonic drinks or electrolyte drinks are particularly suitable as they optimally support the fluid balance and electrolyte levels in the body. Drink around 500 ml of fluid 2-3 hours before the start and drink an additional 200-300 ml 15-30 minutes before the start

Numerous studies and experience reports from professional endurance athletes confirm the benefits of an increased carbohydrate intake of 60 to 120 g per hour during intense physical exertion. The more carbohydrates consumed, the better the athletic performance during the race. The main aim of this increased carbohydrate intake is to prevent or slow down the depletion of carbohydrate stores, increase performance during the race and speed up recovery afterwards.

Unfortunately, gastrointestinal problems can sometimes occur when large amounts of carbohydrates are consumed. These range from abdominal pain, bloating, cramps, urge to defecate and diarrhea to belching, upper abdominal pain, heartburn and nausea. These symptoms can significantly impair the performance-enhancing effects of carbohydrates and often lead to athletes having to abandon the race.

The causes of gastrointestinal problems can be related to many factors: lack of oxygen and blood due to intensive exercise, lack of oxygen at high altitudes, loss of fluids due to heavy sweating, insufficient water intake during activity and the mechanical impact of running. The increased sympathetic tone under stress also restricts digestive functions. In addition, mental stress and anxiety during the race can contribute significantly to the development of gastrointestinal problems.

As the causes vary greatly and are often multiple, it is difficult to clearly identify them. To date, there are only a few studies in endurance sports that deal with this problem. However, one approach to optimizing the tolerance of carbohydrates is to "train the gut". This approach, which was proposed by Rehrer et al. in the 1990s and further developed in the 2000s, assumes that the gastrointestinal system can adapt and improve its capacity to process food intake during exercise by gradually preparing it for the nutritional conditions on race day.

It is therefore advisable to test not only the tolerance and taste of the planned food in the run-up to a competition. It is particularly important to train the gastrointestinal system for a high carbohydrate intake per hour. For intensive training sessions and long endurance units, start with an intake of 50-60 g of carbohydrates per hour and increase this gradually. Make sure you do not neglect your water intake during these sessions.

In endurance sports such as triathlon and trail running, sufficient fluid intake plays a crucial role in maintaining the water balance and general performance. Intake is very individual and depends on the temperature and the athlete, as sweat loss varies greatly. This can be determined by weight tests before and after training or by sweat analysis. Recommendations in sports literature range from 400 ml to 800 ml per hour.

However, fluid is not only important to keep the body hydrated - it is also essential to optimize the absorption and utilization of carbohydrates in the body. The absorption of carbohydrates, whether in the form of gels, powders or other supplements, is strongly influenced by fluid intake. If carbohydrates are consumed in too concentrated a form, this can impair the isotonic effect of the fluid in the body. An isotonic solution has the same osmotic pressure as the blood, which means that it can be absorbed quickly and efficiently by the body. This is particularly important as good hydration is necessary to optimally process the carbohydrates in the small intestine and convert them into energy.

Drink mixes that contain more than 8 g of carbohydrates per 100 ml can lose their isotonic effect. In such cases, the body cannot fully absorb the liquid, which in turn means that the carbohydrates are not optimally processed or the fluid balance is not adequately covered.

Studies and practical experience have shown that liquid carbohydrates - i.e. carbohydrates dissolved in a sufficient amount of water - are often better tolerated by the gastrointestinal system than gels alone. This is because the simultaneous intake of liquid promotes carbohydrate absorption in the small intestine and thus improves the provision of energy. When choosing the right carbohydrate source, care should therefore be taken to ensure that the carbohydrates are dissolved in a suitable amount of water to ensure isotonicity and aid digestion or that water is consumed via additional sources, e.g. at the refreshment stations or via a second flask or bottle without a carbohydrate drink.