New Study Finds Some Sports Drinks Better than Water, But Not All

Prolonged exercise offers great benefits for the body and mind, but it leads to loss of body fluid. What’s worse, dehydration of greater than 2% of body mass can reduce cardiac output, increase perceived exertion, impair thermoregulation, and hamper muscle blood flow.² Advocates of sports drinks have long touted their promise to replace electrolytes, but can they hydrate the body as effectively as water during exercise?

Three Types of Sports Drinks

In the current study, David Rowlands et al., categorize sports drinks as hypertonic, isotonic, or hypotonic. This refers to the concentration of solutes (such as sugars and electrolytes) in the drink relative to body fluids.

Hypertonic Sports Drinks:

Definition: Hypertonic sports drinks have a higher osmolarity than bodily fluids, meaning they have a higher concentration of solutes (e.g., sugars and electrolytes) than the fluids inside the body.

Purpose: These drinks are primarily used for providing quick energy and aiding in glycogen replenishment after intense and prolonged exercise.

Absorption: Due to their high osmolarity, hypertonic drinks are absorbed more slowly than bodily fluids. This can lead to delayed rehydration and can cause gastrointestinal discomfort if consumed during intense physical activity.

Recommendation: Hypertonic drinks are typically not recommended for use during exercise because they can hinder rather than enhance rehydration.

Isotonic Sports Drinks:

Definition: Isotonic sports drinks have an osmolarity that is similar to bodily fluids. The concentration of solutes in these drinks is balanced, allowing for quicker absorption into the bloodstream.

Purpose: Isotonic drinks are designed to quickly rehydrate and replenish electrolytes during moderate to high-intensity exercise.

Absorption: Because the osmolarity of isotonic drinks closely matches that of body fluids, they are absorbed more rapidly and efficiently, aiding in rehydration and maintaining optimal performance.

Recommendation: Isotonic drinks are commonly used during exercise and are generally the preferred choice for most athletes to maintain hydration and prevent dehydration.

Hypotonic Sports Drinks:

Definition: Hypotonic sports drinks have a lower osmolarity than bodily fluids. This means they have a lower concentration of solutes than the fluids inside the body.

Purpose: Hypotonic drinks are mainly used for fast rehydration, especially in situations where quick fluid replacement is required without the need for additional carbohydrates or energy.

Absorption: Hypotonic drinks are absorbed faster than bodily fluids, making them suitable for rapid rehydration. However, they do not provide significant energy or help in sustaining prolonged exercise.

Recommendation: Hypotonic drinks are best suited for athletes who need to rehydrate quickly after short bursts of intense activity or those exercising in hot and humid conditions where fluid loss is high.

In summary, the primary differences among hypertonic, isotonic, and hypotonic sports drinks lie in their osmolarity, absorption rates, and intended uses. Isotonic sports drinks are the most balanced and widely recommended for maintaining hydration and supporting performance during moderate to high-intensity exercise. Hypertonic drinks are primarily for glycogen replenishment after prolonged exercise, while hypotonic drinks are suitable for rapid rehydration without providing significant energy during short bursts of activity.

Researchers also considered the role of ingested carbohydrate (CHO)–electrolyte (CHO-E) (sports drinks) and non-carbohydrate–electrolyte (non-CHO-E) beverages within these categories.

The Latest Research

Rowlands et al. reviewed the studies measuring plasma volume (dPV) in the central circulatory system, relative to the effects of exercise and consumption of water and different sports beverages. Their meta-analysis confirms the traditional thinking regarding hypotonic sports drinks described above. The change in dPV during exercise was different depending on the type of sports drink consumed: hypertonic − 7.4%, hypotonic − 6.3%, isotonic − 8.7%, and water − 7.5%. Athletes using hypotonic sports drinks retained more hydration in terms of plasma volume in the central circulatory system. The reviewers conclude that drinking hypotonic-carbohydrate-electrolyte sports drinks during continuous exercise produces the greatest hydration effect.  

 

References

1. Rowlands DS, Kopetschny BH, Badenhorst CE. The hydrating effects of hypertonic, isotonic and hypotonic sports drinks and waters on central hydration during continuous exercise: a systematic meta-analysis and perspective. Sports Medicine. 2022 Feb 1:1-27.
2. Deshayes TA, Pancrate T, Goulet ED. Impact of dehydration on perceived exertion during endurance exercise: A systematic review with meta-analysis. Journal of Exercise Science & Fitness. 2022 Jul 1;20(3):224-35.