Choosing the best sports drink: Understanding Osmolality – Hypotonic; Hypertonic and Isotonic
Osmolality is a measure of the number of dissolved particles in a fluid. These particles or solids could be maltodextrins, sugars, salt or other electrolytes.
The osmolality of the drink determines the rate at which the fluid moves from the gut and into the bloodstream. A drink with a lower osmolality results in faster absorption than one with a higher osmolality.
Terms-Schlerms!
Hypotonic; Hypertonic and Isotonic:
Hypotonic means that the drink has a fairly low osmolality: It has fewer particles (carbohydrates and electrolytes) per 100ml than is found in body fluids (or blood). Because it is more dilute, it is absorbed faster than water, but because it holds “less” in terms of carbohydrate and electrolytes (less than 4 grams of carbohydrate per 100 mls fluid), it delivers “less”; and thus athletic performance is “less”. This is not an optimal choice of drink for long endurance events.
Hypertonic means that the drink has a high osmolality: The drink has a higher number of particles in 100mls fluid than in body fluid or blood. Because it is more “dense”, it is absorbed much slower than water and can “sit” in the athlete’s gut – causing gastric distress, nausea and general “shloshing around”, sometimes resulting in vomiting. Around 10 grams of carbohydrate or more per 100ml of water makes the sports drink hypertonic. This is not a good choice for hydration during long endurance events, but they can be used to replace carbohydrates after an event, or they can be consumed during a very short “sprint” event – such as a competition that lasts less than 20 minutes.
Isotonic means that the drink has a similar osmolality to body fluid or blood – containing a similar number of particles per 100ml. It is absorbed at approximately the same speed as water. Sports drinks that contain 5-8 grams of carbohydrate to 100ml of water (i.e. a 5%-8% concentration in solution) are isotonic. Because of their efficient absorption, these drinks replace lost fluids rapidly, as well as providing working muscles with a consistent source of carbohydrates and electrolytes.
The TYPE of Carb is equally Important for Athletic Performance!
The type of carbohydrate in a sports drink is as important as osmolality: The best is a blend of carbohydrates, consisting primarily of maltodextrins, some fructose (usually about 2 %) and only very SMALL amounts of glucose. Note that glucose, sucrose or dextrose are not considered ideal primary sources of carb for an endurance drink.
Why Maltodextrins?
Maltodextrins are versatile, longer-lasting carbs: Basically, they consist of a complex grid of glucose-molecule chains, varying greatly in size and length. When consumed, these chains break down into individual units of glucose, providing a fast but steady supply of carbohydrate to the body.
How do I know which Carbs are in my Sports Drink?
A quick squizz at the back of the label will tell you: Find the “Ingredient List”, as labeling laws require that all ingredients must be listed from greatest to least in descending order. So a well-designed sports drink should list the following ingredients in the following descending order: Maltodextrin, then fructose then glucose/dextrose. Maltodextrin, because of its stable delivery system, should be the primary ingredient of the drink (and thus should be listed first).
A Note on Fructose…
If you’re diabetic, your dietician may recommend a sports drinks that has a high content of fructose. (In other words, fructose is listed first under the “Ingredients List”). Medical recommendations such as these make sense! But, for many athletes, fructose can cause significant gastric disturbance during competition! Not an ideal place to find yourself in! So unless you’re diabetic, you’ll want to avoid sports drinks that contain fructose as the primary source of carb – that is, where fructose is listed first on the “Ingredient listing”. If fructose appears second or third on this list, then the drink presents no gastric risk, as fructose is not the primary source of carb, but rather, fulfills a supportive function by topping up the glycogen in the liver.
And the Winner is…
For middle and long endurance events, the drink of choice is..
- A 5-8% carbohydrate blend – that is, an isotonic drink where the absorption rate of the fluid, the carbohydrates and the electrolytes is similar to the absorption rate of pure water.
- A blend of primarily maltodextrins, some fructose and even smaller amounts of glucose, or similar simple sugars.
Why not Pure Water?
Whilst water is THE best and most essential daily drink, it does have its limitations in terms of hydration during athletic events.
Here are some of the issues when hydrating with water alone:
- Water turns off the thirst-mechanism before rehydration is complete. 1
- Water lacks electrolytes and carbohydrates which fuel optimal performance. 2
- Water, since it has no flavour, does not encourage drinking as much as a lightly flavoured drink does. 3
Technical Stuff: Osmolality and Osmolarity
Osmolality is the measure of osmoles of solute per kilogram of solvent (osmol/kg or Osm/kg) whilst osmolarity is the measure of osmoles of solute per litre (L) of solution (osmol/L or Osm/L). Osmolality and osmolarity in terms of sports drinks are practically equivalent.
EnduraPower contains a blend of carbohydrate in a 6%-7% concentration that promotes both fast fluid uptake, whilst maintaining stable blood glucose levels.
EnduraPower achieves the fine balance between effective hydration, energy delivery, rapid gastric emptying and the maintenance of stable blood glucose levels, without causing gastric upset.
References:
1. Wilk, B. and Bar-Or, O. J Appl Physiol 80:1112-1117, 1996.
2. Below, P.R. et al. Med Sci Sports Exerc 27:200-210, 1995.
3. Passe, D.H. et al. Appetite 35:219-229, 2000.