Nutritional management of athletes and impact of glycemic index on oxygen efficiency

The notion of physical fitness encompasses three primary components: the body's capacity to perform physical activity, its ability to adapt to disruptions in homeostasis during exertion, and the ability to rapidly restore resting homeostasis during the recovery phase post-exercise. Consequently, physical fitness can be defined as the capability to sustain prolonged or intense physical exertion involving major muscle groups, with gradually increasing fatigue and associated changes in bodily homeostasis. Individuals who engage in regular physical activity exhibit superior oxygen utilization due to enhanced oxygen uptake and delivery to tissues, resulting in more efficient muscle oxygenation during exertion.

The nutrition of athletes plays a crucial role in both the preparatory phase and the recovery process. The primary goal of nutrition and training is to enhance performance capacity by providing the body with essential nutrients. In endurance sports, the demand for energy and nutrients is particularly high, making adequate energy supply, regular supplementation of building blocks, as well as micronutrients and electrolytes, essential. Intense physical exertion can lead to the depletion of energy substrates (primarily muscle and liver glycogen), disturbances in water and electrolyte balance, and nutrient deficiencies. These negative effects reduce physical performance and muscle efficiency. Therefore, adhering to proper nutritional guidelines should be an integral part of the training process. Research indicates that a balanced diet, often supplemented, significantly impacts energy release during exertion and the regeneration of energy substrates. At the International Conference on Sports Nutrition in Lausanne, held 34 years ago, it was emphasized that dietary habits influence performance capacity. Proper nutrition, both in quantity and quality, before, during, and after training and competitions, contributes to achieving optimal sports results. Currently, there are many conflicting trends in athlete nutrition. Some recommend a high-carbohydrate diet, while others advocate for protein- and fat-based diets. However, according to current, scientifically validated recommendations, a high-carbohydrate diet is most suitable for endurance athletes. Over 60% of energy should come from carbohydrates, 25% from fats, and 1.4–1.9 g/kg of body weight from protein. Table 6. Muscle glycogen content depending on diet type: Diet type – Glycogen in 100g muscle (g) – Work time (min): Normal mixed diet – 1.75 – 126; Protein-fat diet – 0.63 – 59; High-carbohydrate diet – 3.3 – 189.

The availability and impact of carbohydrates on the body, determined by their conversion rate into glucose, define the glycemic index (GI). The GI value indicates how quickly consumed carbohydrates become available to the body, particularly for active muscles. Products with a GI of 0–55 are classified as low-GI, those between 55–70 as medium-GI, and above 70 as high-GI. Analysis of international literature does not provide a definitive recommendation for the optimal GI in endurance athletes. Some studies suggest that low-GI products extend exercise time or distance, while others do not confirm this effect. Differences arise from varying methodologies and a focus on single meals rather than overall diet. Nevertheless, long-term intervention studies are increasingly conducted. Continuous substrate supply to muscles is crucial for maintaining glycogen levels. Evidence indicates that a low-GI diet improves exercise performance, serving as direct proof of the effectiveness of nutritional strategies. The general recommendation to consume low-GI products before exercise is justified, as it ensures sustained energy delivery. Such meals should be consumed 1–2 hours before exercise to avoid digestive issues. For rapid post-exercise recovery, high-GI products, preferably in liquid form, are recommended. Within the first 4 hours post-exercise, 1–1.2 g/kg body weight of carbohydrates should be consumed, equating to 240–288 g for a 60 kg individual. If recovery lasts at least 24 hours, exclusively high-GI meals are unnecessary—balanced low-GI meals suffice. Beyond enhancing endurance performance, low-GI products are recommended for preventing diabetes and other metabolic disorders. Avoiding sharp blood glucose fluctuations prevents excessive insulin release, reducing insulin resistance risk. I encourage all athletes, recreational and professional, to adopt mindful nutrition, ensuring adequate caloric intake. Carbohydrates as the primary energy source should have a low or medium GI, while high-GI products should be limited to post-workout meals. Below is an example of a low-GI day (average daily GI = 37): Breakfast: Mackerel paste sandwiches, pear salad; Second breakfast: Low-fat quark with dried morels and almonds; Lunch: Whole-grain pasta with baked salmon; Afternoon snack: Natural yogurt with roasted oat flakes, green banana, and dark chocolate; Dinner: Rye burger with chickpea patties, romaine lettuce, and tomato.