Hypotonic vs Hypertonic: Isotonic Sports Drinks

Understanding the key differences between Hypotonic and Hypertonic (Low vs High sugar) sports drinks first requires a brief understanding of 'tonicity'. 

The 'tonicity' of a drink measures the relative concentration of sugars and salts compared with the concentration found in the blood.

• A hypotonic sports drink is low in tonicity
• While a hypertonic sports drink is high in tonicity. 

The difference between the two determines the direction and extent of fluid absorption after consumption.
 

The science of sports drink 'tonicity' can significantly impact your hydration in training and competition. Most sports drinks are isotonic, meaning they have a similar concentration (or tonicity) to your blood. 

However, the best sports for rehydration are hypotonic, as their low tonicity drives fluid absorption. These drinks contain less than 6% carbohydrates. Low sugar levels are ideal because fluid absorption in the body primarily occurs in the small intestine and requires some glucose.

Despite dehydration remaining a significant barrier to peak endurance performance, sports drink formulations haven't substantially changed since they were invented over 50 years ago and had two fundamental shortcomings:

1. Tonicity – Most sports drinks have too much sugar for optimal hydration in the small intestine.
2. Gut hydration – All sports drinks ignore the hydration potential of the large intestine, which can absorb up to 5L of fluid per day.

PREPD is a hydration enhancer designed to address these two shortcomings to boost the impact of other sports drinks and water.

A two-step hydration system consumed pre- and post-exercise, the PREPD drinks feature a unique sustained fibre clinically proven to enhance gut hydration and have low tonicity (low in sugar).

In a recently published clinical trial, PREPD demonstrated significantly better hydration in elite AFL football players before, during, and after exertion than those only consuming leading sports drinks.

Isotonic vs hypotonic vs hypertonic, most sports drinks are isotonic and typically contain between 6-8% carbohydrates, providing athletes with a balance of energy, electrolytes, and fluids.

However, most isotonic drinks are slightly hypertonic, such as Gatorade Orange and Powerade Mountain Blast (Mettler et al. 2006).

Hypertonicity slows hydration by delaying gastric emptying of fluid from the stomach into the small intestine, where it is absorbed. Often, this can cause gastrointestinal upset and leads to the feeling of fluid 'sloshing in the stomach after consumption.

Isotonic sports drinks are, therefore, best used for short, high-intensity exertion where energy is the priority rather than hydration. Popular sports and electrolyte drinks currently marketed as being isotonic include:

• Gatorade
• Gatorade Endurance
• Powerade ION4
• Staminade
• Maximus
• Science in Sport – GO Electrolyte
• Pure Sports Nutrition – Pure Electrolyte Hydration
• Endura Rehydration Performance Fuel
• GU Hydration Drink Mix
• Nuun Performance
• Pro4mance Produce
• Isowhey Sports Electrolyte Formula
• Bindi Sports Hydration

Only a few sports drinks are marketed as hypertonic – having a higher concentration than the blood – and typically have over 10% carbohydrate composition.

These drinks' goal is to provide a significant source of energy rapidly. This additional sugar content comes at the expense of hydration. It can become especially problematic for athletes exerting for long periods or in the heat.

Therefore, hypertonic sports and recovery drinks are most appropriate in scenarios where taking in energy and nutrients is the main priority and dehydration is insignificant.

Popular sports and electrolyte drinks currently marketed as being hypertonic include:

• GU Roctane Energy Drink Mix
• Lucozade Energy

Hypotonic sports drinks have less than 6% carbohydrate content, and the fluid is absorbed faster than isotonic drinks (Rowlands et al., 2011). 

The lower concentration of hypotonic drinks allows for faster fluid uptake than isotonic drinks.

Hypotonic sports drinks are, therefore, fantastic for any exertion lasting over an hour or where hydration is a priority.

Other food and fuel sources such as gels, bars, and snacks can better meet your energy needs, best consumed with some separation from substantial fluid intake.

Popular sports and electrolyte drinks currently marketed as being hypotonic include:

• Hydralyte Sports
• Mizone
• SOS Hydration Drink Mix
• G Active and G2
• Powerade Zero
• Endura Rehydration Low-Carb Fuel
• Nuun Electrolytes
• Shotz Electrolyte tablets
• Skratch Labs Sport Hydration Drink Mix
• Aqualyte Solution
• High 5 Zero
• Pro4mance Prodrate
• PREPD Recover (Post-Workout Hydration Enhancer)

Choosing the right sports drink depends on your individual needs and involves trade-offs between fluid absorption and energy requirements. Isotonic drinks can be considered 'energy' drinks rather than 'hydration' drinks due to being slightly hypertonic.

Where hydration is a priority, we recommend hypotonic sports drinks during exertion to promote faster absorption.

Whether your favourite electrolyte drink to meet your performance needs is hypotonic, isotonic, or hypertonic, PREPD can boost your hydration effectiveness and even enhance the body's water absorption.

PREPD Prime should be consumed 10-18 hours before intense exertion for better hydration when you need to perform, and PREPD Recover should be consumed immediately after exertion for better rehydration in recovery.