WHO Guidelines for ORS

For optimal hydration some glucose is required to facilitate fluid absorption in the small bowel via the sodium : glucose co-transport system which aids water absorption.

SOS contains a small amount (2.5-3.5g per serve) for this purpose. Sports drinks typically contain 5 times more glucose than the same sized SOS serve. Too much sugar can slow gastric emptying and absorption of fluids. Zero sugar hydration drinks, whilst presented as a ‘healthy alternative’ to sports drinks are also less effective at hydrating due to no glucose facilitating fluid absorption.

The major electrolyte involved in fluid balance in the body is sodium. Sodium is also the electrolyte that we lose in highest concentrations through sweat. Knowing the importance of sodium regulation for fluid balance, muscle contraction and nerve impulse regulation, the amount of sodium in SOS serves two main functions:
• Replace the sodium that is lost through sweat
• Aid the absorption of water in the body

Osmolarity refers to the number of particles in a solution. When applied to a hydration formula osmolarity is used in reference to absorption of fluid via natural osmotic mechanisms in the body to drive fluid via the blood stream into cells.

Oral Rehydration Solutions (ORS)  are hypotonic formulas, which means they have a lower osmolarity than blood.
Most sports drink are Isotonic (same as blood stream) or Hypertonic (higher than blood stream). This results in a slower and less effective absorption rate than an ORS.

In order to aid the absorption of water, sodium and a small amount of glucose (sugar) work together in the gastro-intestinal system. This occurs through the Sodium : Glucose co-transport system in the small intestine. When a molecule of glucose crosses the membrane from the small intestine into the blood stream a molecule of sodium binds to it and crosses also. Through osmotic forces water will follow sodium and through this process facilitate the water being absorbed into the blood stream to maintain blood volume and allow the body to continually cool itself.

Potassium further assists with sodium regulation in the body also.
Knowing that glucose is necessary in small amounts for optimal absorption may change the way you look at completely sugar free options that invaribly use artificial sweeteners for flavour and are not able to have the same benefits of absorbtion.

Sports drinks typically contain too much glucose (sugar) and not enough sodium to facilitate this process. The large amount of sugar in sports drinks can often slow gastric emptying whilst exercising, leading to a bloated feeling as the fluid will not move through the gut. Not only is this uncomfortable but it also inhibits the absorption rate of the fluid.