Sports Nutrition, Hydration and Performance – Part 2
Written by Robert Coyle
Food is the fuel that enables athletes to perform to the best of their ability. The diet of an athlete is a fundamental aspect to their training routine. Exercise and eating should form a positive relationship in order to ensure an athlete remains healthy while maximising their performance.
Each nutrient contributes to the overall performance of an athlete; however depending on the type of athlete the requirements for specific nutrients may vary. The energy and nutritional needs of athletes will also fluctuate at different times during their training programme. The food intake of an athlete before an event should contain an increased amount of carbohydrates to develop the glycogen store within the muscles, this is known as carbohydrate loading. The recommended form of carbohydrate loading involves decreasing the training volume while maintaining intensity. In terms of carbohydrate intake the amount should increase from 50% to 70-75% of energy, resulting in a decrease intake of fat foods. The energy consumption should remain the same, but a larger volume of food will be required as carbohydrates are less energy dense than fat foods (van Loon, 2012).
It is essential for athletes to rebuild their glycogen stores quickly following exercise as there is a critical time period where the synthesis of the glycogen store is at its greatest. The type and amount of carbohydrates consumed will determine the rate at which the glycogen store is replenished. Foods with a high glycaemic index such as refined bread and cereals, and sugary products are deemed a better option as they provide readily available source of carbohydrates, whereas foods with a low glycaemic index for example wholemeal products should only make up a third of the recovery meal. The individual requirements of the athlete must be taken into consideration in terms of total energy needs, specific training needs and feedback from training performance. Overall the general recommendations for carbohydrates directly after exercise (0-4 hrs) are 1-1.2 g per kg of bodyweight per hour. When choosing the post-exercise meal the athlete should take into consideration the period before the next exercise session, as the rate of glycogen will have to be greater if the time period is only short (< 8hrs). The rate of glycogen synthesis does not vary between liquid or solid forms of carbohydrates (Burke L., et al., 2004).
Protein is an important component in an athlete’s diet as it is responsible for muscle synthesis and for providing essential amino acids to neurotransmitters and hormones (O’Brien N., 2010). According to the European Food Safety Authority (EFSA) the Population Reference Intake (PRI) for sedentary adults is 0.83 g of protein per kg of bodyweight per day (EFSA, 2012). The United States Department of Agriculture (USDA) have a similar recommendation to EFSA at 0.8 g of protein per kg of body weight (USDA, 2010). During endurance exercise the rate of protein oxidation increases and during strengthening exercise there is an increase in muscle synthesis and repair. Therefore is it recommended that there should be a slight increase in the protein DRI 1.2 -1.8 g per kg per body weight, in order to accommodate for any increase in requirements. This recommendation will vary slightly between endurance and strengthening athletes. This increase can be easily met by changing an athlete’s diet without the use of any supplements (American Dietetic Association, 2009).
Fat is the predominant energy fuel for low intensity, endurance exercise. Fat is stored in adipocytes (fats cells), with some being stored in skeletal muscle tissue, fat accounts for 95% of the body’s total endogenous energy reserve (van Loon L.J.C., 2012). Fats release more energy (9 kcal per gram of fat) than carbohydrates but they do so at a slower rate. Depending on the intensity of the exercise and the availability of substrates, the amount of fat required can vary. Recent studies have suggested that a diet that comprises of 30-35% carbohydrate, 30% fat and 20% protein, with the balance (20%) of total calories supplying the substrates used in exercise, is optimal for athletes (Pendergast D. et al., 2000). The 30% of fat should be split equally between fatty acids so that the proportion of energy from fatty acids should be no more than 10% saturated fat, 10% polyunsaturated fat, 10% monounsaturated fat, and should include sources of essential fatty acids (USDA, 2005).
Vitamin and minerals play a huge role in energy production, maintenance of bone health, immune functioning, protection against oxidative damage, synthesis and maintenance of muscle tissue. As long as an athlete maintains a healthy well balanced diet all the micronutrients should be supplied, even if exercise increases the turnover and loss of micronutrients from the body. There are some micronutrients that are more important than others in terms of improving an athlete’s performance. Such as the B vitamins as they are associated with energy production and the building and repair of muscle tissues. Vitamin D is involved in bone health and development of the nervous system in muscles. Antioxidants such as Vitamin C and E are required to protect against oxidative stress. In terms of the minerals Calcium is needed for the regulation of muscle contraction and bone health, Iron for the formation of oxygen carrying proteins and hormones involved in energy production, Zinc which has a vital role in building and repairing muscle tissue and in the immune system and Magnesium is required for cellular metabolism (American Dietetic Association, 2009).
Overall, it is essential that not only does an athlete maintain a healthy diet but ensures that they receive the correct proportion of energy from each macronutrient which is Carbohydrates, fats, proteins.
- American Dietetic Association (2009). Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance.
- Burke L., Keins B., and Ivy J., (2004). Carbohydrates and fat for training and recovery. Journal of Sports science; Volume 22, Issue 1.
- EFSA (2012). Scientific Opinion on Dietary Reference Values for protein. EFSA Journal 2012;10(2):2557
- O’Brien N., (2010). Lecture notes on Advanced Nutrient Metabolism. UCC
- Pendergast D., Leddy J., Venkatraman J. (2000). A perspective on fat intake in athletes. Journal of American College of Nutrition, Vol. 19, No. 3, 345-350 (2000)
- USDA, (2005). Dietary Guidelines for Americans. United States Department of Health and Human Services and USDA.
- USDA, (2010). Dietary Reference Intakes: RDA and AI Vitamins and Elements, National Academy of Science. Institute of Medicine. Food and Nutrition Board
- Van Loon L.J.C., (2012). The Human Engine. The Netherlands; Oggi communicatie.