In this article Professors Asker Jeukendrup and Michael Gleeson who are the authors of Sport Nutrition 4th edition explain why nutrition is an important factor for Olympic athletes aiming to win a medal in their sport. Using excerpts from their book, which is widely regarded as the most comprehensive and detailed resource for people wanting to understand the science underpinning the current guidelines on nutrition for athletes, the professors explain just how important the composition, amount, and timing of food, beverage, or supplement intake is for sport performance.

Nutrition plays an essential role in exercise and sport because it is important for health, adaptations to physical activity and exercise, weight maintenance, and exercise performance. Nutrition influences nearly every process in the body involved in energy metabolism, from performing physical activity to adaptation to training and recovery from exercise. Yet if we look back 50 years or more, nutrition was largely ignored by those involved in professional sport, and the dietary practices of athletes were often based on folklore, trial and error, or personal experience and opinion. Nowadays, good nutrition—in terms of the composition, amount and timing of food and beverage intake, and the use of selected supplements—is considered essential to maximising performance, health, and recovery.

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Nutrition affects every aspect of human function, so it is an important factor to consider if we want the body to function at its best. Next to training and recovery, nutrition is the third pillar of performance. Nutrition provides fuel for muscular work and supports optimal focus and cognitive function. Good nutrition also supports our recovery from exercise, growth and adaptation, immune functions, and many other physiological systems. However, nutrition is rarely ever a quick fix: like training, it involves consistent and repeated meals that are optimised for the athlete’s goals. Weight loss, muscle gain, or increased mitochondrial density will not occur overnight, but will happen as the result of the longer-term interplay between training, physical activity, and the intake, composition, and timing of meals.

Most competitive sports require moderate to high-intensity actions that are either sustained for considerable periods of time (e.g., long-distance running and cycling events) or are interspersed with periods of less-intense physical activity over the course of a few hours (e.g., rugby, football, hockey, basketball, tennis, and golf). In most team games, match play involves not only running but also various in-play actions, such as jumping, tackling, and hitting, kicking, or throwing a ball. In addition, mental functioning is important for the timing of ball strikes and tackles, placement accuracy, quick reactions, rapid decision making, and maintaining concentration. All of these are affected by fatigue, which tends to result in slower reactions, fewer high-intensity actions, and more errors. Hence, minimising fatigue compared to the opposition is an important strategy in many sports, and nutrition, as well as the will to win, skill and tactics, can play an important role here.

Appropriate nutrition can address two of the major contributors to the development of fatigue: carbohydrate depletion and dehydration. Since the beginning of the 20th century, carbohydrate intake has been known to be related to exercise performance. The availability of carbohydrate as a substrate for skeletal muscle contraction and the brain is important for the performance of prolonged exercise and the performance of intermittent and continuous high-intensity exercise. Because carbohydrate is the most important fuel for the central nervous system, various cognitive tasks and motor skills that play a crucial role in skill sports may also be affected by carbohydrate availability. Various strategies have been developed over the past 30 years to optimise carbohydrate availability and athletic performance. Generally, this can be achieved through carbohydrate intake (e.g., pasta, rice, bread, fruit, and starchy vegetables) before exercise to replenish muscle and liver glycogen stores and carbohydrate intake (e.g., sports drinks, gels, and bananas) during exercise to maintain blood glucose levels and high rates of muscle glucose oxidation derived from the plasma. 

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Dehydration due to heavy sweating during prolonged exercise (especially in hot weather) can also contribute to fatigue. Athletes should start their events well hydrated and during exercise they should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to prevent excessive dehydration (reductions in body weight greater than 2%). Because people vary considerably in their rates of sweating (and, of course, sweating rate depends greatly on environmental conditions and exercise intensity), athletes should develop customised fluid replacement programmes to achieve this goal. 

In addition, a few dietary supplements such as creatine, nitrate, beta-alanine, sodium bicarbonate, and caffeine can produce small improvements in performance in some individuals. Supplements of certain vitamins and minerals (e.g., vitamin D, iron, magnesium, and zinc) are also common to avoid deficiencies of essential micronutrients that support optimal health and performance.

Recovery starts immediately after the competition ends, and nutrition (particularly getting enough protein and carbohydrate) is crucially important at this time for muscle repair and refuelling, particularly in team sports when the next match can be less than 72 hours away. Appropriate food choices and timing are also important to allow athletes and games players to perform hard training, avoid illness, reduce injury risk, maintain mental concentration, sleep well, maintain an appropriate body weight and composition, and recuperate from injury.

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To summarise, in many sports, nutrition matters very much indeed. Good nutrition can improve endurance, delay both physical and mental fatigue, and hasten recovery. It is also important to ensure that nutrition is personalised to the needs and goals of each person because there is no single diet that is best for all athletes and all goals. The optimal diet will also vary from day to day to suit the needs for training, competition, and recovery.

The important take home message for athletes is that a good diet will not make an average athlete become elite, but a poor diet will prevent an elite athlete from achieving their performance potential and seriously limit their chances of winning a medal in most Olympic events. 

Header photo by Luca Dugaro