Nutrition Tips - Sports Drinks
What should a sports drink look like? They have pretty colours, fancy ingredients and vary in taste dramatically. But take it all away and what should an effective sports drink contain and what is just marketing hype?
Carbohydrate
Amount
We all know that carbohydrate is important for performance and to couple it with fluid and consume it from one source is a logical end point - hence the advent of the sports drink. Most sports drinks are between 4-8% carbohydrate. This is the amount of carbohydrate that is accepted to ensure suitable transition time through the stomach. Carbohydrate volumes higher than this can slow down the rate of emptying of the stomach and lead to the fluid sitting in the stomach for longer than expected. The body is highly adaptable and even though these levels are accepted norms the body can be trained to accept concentrations higher than this. In practice elite athletes regularly consume fluids in higher concentrations than 8% (flat coke undiluted is around 11%) to meet their high requirements.
Type
Over the last few years recent research has looked at the type of carbohydrate and how it affects performance. Historically when we talk about carbohydrate in sports drink it has mainly been glucose or sucrose. The problem with glucose is that you can quickly overload its absorptive capacity and this becomes a limiting factor in getting sufficient carbohydrate sources to the working muscle to sustain high intensity performance.
Inventive scientists have now started manipulating the type of carbohydrate to increase the amount absorbed and delivered to the working muscle. This has had a flow on effect into the sports drink market with companies advertising their products as having unique formulas for faster delivery of energy to the muscles. This is achieved by adding other carbohydrates such as fructose and/or Maltodextrins to the sports drink in combination with glucose. These carbohydrates effectively have different absorption sites meaning that when the glucose absorption site is full then these other carbohydrates can still be absorbed. This leads to higher amounts of exogenous carbohydrates (carbohydrates from outside the body) being used by the muscle and sparing the bodies stores.
Electrolytes
These have always been a major marketing buzz word associated with sweating, dehydration and sports drinks. Electrolytes are mineral salts the body loses in sweat during exercise. The major electrolyte of interest is sodium. Sodium is important in a number of bodily functions from the maintenance of blood volume to facilitating nerve impulses. When a lot of sodium is lost in sweat it can have a major effect on performance and bodily functioning.
Sodium is often implicated in severe "exercise associated muscle cramps" but has been over emphasised in the common problem of cramps (will look at that another time). Sodium is identified as the most important electrolyte for replacement due to sweat containing large amounts of sodium. Sodium intake during exercise also facilitates faster rehydration and carbohydrate absorption. Athletes should aim for sports drinks with sodium concentrations in the range of 50mg/100ml (20mmol) - 120mg/100ml (50mmol). Obviously the salty flavour of sports drinks will increase as sodium concentrations increase but this is not such a bad thing as salty flavour actually increases the desire to drink which improves voluntary hydration.
Other electrolytes such as potassium, chloride and magnesium are important electrolytes within the body but research has shown that they are not lost at levels (that are difficult to replace) that adversely effect performance in the average athlete. I know there will be a lot of people out there saying magnesium is essential but there is still no credible evidence that suggests that magnesium losses through sweat is a limiting factor in performance in athletes (again a discussion for another time).
Concentration - Hypotonic vs Isotonic
Sport drinks usually fall into two categories of concentration based on their osmolality (the number of particles in a solution) - Hypotonic or Isotonic. Hypotonic solutions are less concentrated than the bodies fluids therefore, will move into the body from the intestine more rapidly than potentially an isotonic solution which is the same concentration as the body's fluids. This is a good thing when you are loosing body fluid at an alarming rate but not a good thing when you are losing fluid slowly but consuming hypotonic fluid regularly.
Hypotonic sports drinks usually contain less electrolytes and carbohydrates than isotonic sports drinks. By having less sodium and carbohydrate they are going to be less effective at rehydrating and maintaining carbohydrate delivery during high intensity exercise on their own.
So when looking for a sports drink that is right for you ask yourself - "What are you trying to get out of it?" Is it carbohydrate, sodium, fluid, or taste and how will that sports drink then affect your other food and fluid intake during training and a race (ie how will it interact with gels or solid foods)? These are all important questions that need to be asked when looking for a sports drink that works for you and improves performance rather than just being a colourful alternative to water.
Greg Shaw, Australian Institute of Sport, Sports Dietitian

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