Advice on sports nutrition is now firmly anchored in science. General guidelines on sports nutrition improve when the advice considers such things as the athlete’s personal characteristics and training schedule, as well as the type of sport. It is up to (sports) dieticians to provide such tailor-made advice.
Marietje Vierdag won gold in the 100 meters freestyle swimming for the Netherlands at the Olympic Games in Amsterdam in 1928. She stayed with a host family during the games and had to eat what she was served. To serve sporters with identical foods is now impossible to imagine. The successful short distance runner Usain Bolt was hooked on chicken nuggets at the 2008 Beijing Games. Top tennis player Novak Djokovic follows a gluten-free diet. These top athletes require individual customization based on proven general guidelines.
General advice on a good diet also applies to athletes. The Guidelines for a Healthy Diet of the Dutch Health Council and in line with these guidelines the Wheel of Five of the Netherlands Nutrition Centre form the basis for advice on sports nutrition. But for athletes it is not enough to meet the need for essential nutrients and preventing chronic diseases: they want a diet that delivers the best physical performance. Due to their above-average physical activity and thereby higher energy requirement, athletes have more free choice space in the Wheel of Five and a knowledgeable (sports) dietician will use this space with personal nutritional advice to contribute to the performance of an athlete.
A few months before the Olympic Games in Rio in 2016, three renowned North American agencies released a position paper including the latest state of the art in sports nutrition. This review article, with characteristics of a reference book, delivers helpful recommendations for dieticians to assist athletes in their food choices. The most important advice is presented hereafter. The review article is available free of charge (http://dx.doi.org/10.1016/j.jand.2015.12.006) and is a must read for those giving nutritional advice to sporters.
Energy is the cornerstone of sports nutrition: the body needs fuel; the number of calories determines the space for the intake of nutrients and the energy intake has an effect on the body composition. Both the amount and moments of the energy intake are important. Cyclists, for example, are afraid to encounter a sudden occurring hunger during an uphill climb. The energy requirement increases considerably due to intensive sports. Running a marathon costs almost 3,000 kcal. During the 2008 Games in Beijing, the legendary swimmer Michael Phelps burned every day no less than 12,000 kcal. He ate among other things omelettes with five eggs, pancakes, and pasta. Weightlifting, archery, and diving, however, require little extra energy during the competition. Correct energy intake requires customization for different sports.
Carbohydrates and protein
Of the four energy suppliers (fat, carbohydrates, protein, and alcohol), the protein and carbohydrate supply are of special importance for athletes. Protein is needed for muscle building, maintenance, and recovery and for an average adult the daily recommendation is 0.8 grams per kilogram of body weight. For athletes, the recommended range is 1.2 to 2.0 grams/kg/day and for short periods with intensive training or energy restriction, the requirement is often even higher. The position paper indicates that there is good evidence that 20-30 grams of protein intake during or after exercise leads to more protein formation in the body, among which the muscles. The quality of the protein is also important, and the position paper points out that dairy protein is of good quality for athletes.
Carbohydrates are an important energy source for athletes and this macronutrient contributes to the maintenance of endurance performance. The table shows the recommendations for carbohydrate intake and it shows that more intensive exercise requires more carbohydrates. The figures indicate that the carbohydrate recommendations for top athletes also apply to recreational athletes, but that the recommended amounts differ.
Every person loses water daily through breathing, faeces, urine, and perspiration. An athlete keeps body temperature under control through sweating. Working muscles produce heat as a by-product and the body has to lose heat and for that sweating is important. The loss of fluid during exercise may amount to a maximum of 2% of the body weight. For most athletes and sports, a fluid intake of 0.4 to 0.8 litres per hour is sufficient not to exceed the critical limit of fluid loss. When converting general guidelines into personal advice, dieticians must among other things consider the tolerance and experiences of the athlete. For that advice, it must be known how much fluid the athlete loses during exercise to compensate for that amount. Drinking too much is not beneficial to performance and during sports this mainly occurs in recreational athletes. These sporters sweat less than top athletes and are more likely to think that drinking (a lot) is good.
Micronutrients and Supplements
Physical exertion puts pressure on the metabolism of the body. Micronutrients are needed for countless metabolic processes to run smoothly. For athletes, the most critical micronutrients are iron, vitamin D, calcium, and antioxidants. However, the position paper is reserved about any beneficial performance effects of dietary supplements. Supplements with vitamins and minerals are not necessary with an energy-rich diet obtained with foods that contain a high density of nutrients. Nutritional supplements should only be considered when the diet is inadequate. Beneficial effects on sports performance have been reported for a number of substances: creatine, caffeine, sodium bicarbonate, β-alanine, and nitrate. Sodium bicarbonate, for example, improves performance during high-intensity physical exercise.
Tailored advice for an athlete takes the general guidelines about good nutrition and sports nutrition as a starting point. Knowledge of the athlete’s training and competition schedule is required for a translation into individual advice. As a result, the diet will vary per day and throughout the day. Sports nutrition must optimally support the individual sports schedule. A dietician should also monitor an athlete’s body composition. This is especially true for athletes in sports with different weight classes, such as boxers and judoka.
With a tailor-made advice, the (sports) dietician must consider matters such as performance goals, food preferences, physical characteristics of the athlete and the circumstances during sports. For example, more water loss will occur at high temperatures and humidity. The advice before, during and after exercise also differs. In this translation to individual customization, the (sports) dietician, with creativity, knowledge about nutrition and practical experience, provides added value for both recreational and top athletes.
Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietetics of Canada, and the American College of Sport Medicine: Nutrition and athletic performance. J Acad Nutr Diet, 2016; 116: 501-528.
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