Sports Nutrition, Hydration and Performance – Part 1

An athlete’s diet has a significant impact on their performance, especially leading up to and during an important event. Specific nutritional recommendations have been established for athletes for before, during and after an event, in particular for fluid intake.

Water is an essential component of an athlete’s diet. The body is composed of 50-60% of water which equates to between 30 to 50 litres. It is very important to keep the body’s total water content constant, as dehydration can hinder an athlete’s performance. Water is lost from the body through sweat and evaporative losses, which increase dramatically during exercise and can result in more than 2% loss in body weight.

Dehydration causes a fall in plasma volume, which means that less oxygen can be transported around the body. This results in a rise in body temperature which is associated with an increase in muscle glycogen breakdown and can cause premature fatigue. Hypernatremia, low plasma sodium, is associated with loss of electrolytes in sweat. This is dangerous as electrolytes are associated with maintaining fluid balance. The body should be kept hydrated at all times during exercise to ensure cognitive and coordination functions are optimal (O’Brien, 2010).

Prior to an event, the goal is to ensure that any fluid and electrolyte deficiency is correct. Hydrating can begin progressively about 4 hours before the event. 5-7 ml of fluid per kg body weight is advised. Studies have shown that hyperhydration provides no clear physiological or performance advantages over euhydration, which means that the body’s water content is stable. Depending on the sport, fluid intake during exercise is also recommended to account for all the water lost from sweating. Rehydration after exercise is of great importance to revitalise the body and to counteract all the water and electrolytes lost during exercise (American Dietetic Association, 2009).

There is an on-going debate over whether water or sports beverages are most beneficial for an athlete. Both fluid types work efficiently in maintaining hydration levels, but in terms of supplying energy and maintaining electrolyte balance during exercise a sports drink is the better option (van Loon, 2012). Sports beverages are more beneficial to endurance athletes who train for longer than thirty minutes (O’Brien, 2010).

The carbohydrate content of a sports drink is recommended to be 6-8%. It can be used as another source of energy which will delay fatigue. The sodium content in sports drinks act as an electrolyte and helps maintain blood volume which aids in transporting oxygen around the body. Sports beverages are less beneficial to those who exercise for less than thirty minute as water lost through sweat and therefore dehydration is the main concern for them. For exercise routines that are less than thirty minutes, there are insufficient amounts of the glycogen store being used to truly benefit from an intake of a sports drink (American Dietetic Association, 2009).

Recent finding have revealed that milk can be regarded as one of the best recovery fluids for resistance exercise due to its high nutrient content. It was found that milk is more effective at replacing sweat losses and maintaining euhydration than plain water or sports drinks (Shirreff et al., 2007). This is due to the fact that milk contains all of the essential amino acids which are required to stimulate muscle protein synthesis. Carbohydrates within the milk and from other sources stimulate the release of insulin when ingested. Insulin and amino acids work together to increase the net muscle protein balance which is the balance of amino acids in the arteries and veins. This then stimulates net muscle protein synthesis and muscle growth (Elliot et al., 2006).

In conclusion, what we can say for sure is that regardless of the type of fluid consumed, it is essential that athletes remain hydrated at all times especially in preparation, during and after an event.


  • American Dietetic Association (2009). Position of the American Dietetic Association, Dietetians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance.
  • Elliot T.A., et al. (2006). Milk ingestion stimulates net muscle protein synthesis following resistance exercise. American College of Sports Medicine.
  • O’Brien N., (2010). Lecture notes on Advanced Nutrient Metabolism. UCC
  • Shirreff S. et al., (2007) Milk as an effective post-exercise rehydration drink. British Journal of Nutrition; UK.
  • van Loon L.J.C., (2012). The Human Engine. The Netherlands; Oggi communicatie.

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