You have probably come across the supermarket shelf of isotonic drinks and wondered what they really are and why you might need them.
Rosa, sports nutritionist at INDYA, explains.
What Is an Isotonic Drink and What Is It For?
First, we need to understand “isotonic”, using water as a comparison. Water contains fewer solutes than an isotonic drink: fewer minerals and no carbohydrates, making it usually hypotonic.
An isotonic drink has a concentration of solutes, here minerals and carbohydrates, similar to the human body’s, replacing electrolytes and some energy during physical activity. A drink containing more solutes than our body fluids would be hypertonic.
These drinks are therefore balanced and specifically designed to help maintain fluid balance. Isotonic drinks come with or without carbohydrates, as carbohydrates are not essential to their classification. Electrolyte content makes them isotonic; adding carbohydrates also provides quick energy. They usually contain adequate minerals, particularly sodium, potassium and chloride. Carbohydrate-containing versions usually combine glucose, fructose, starches or maltodextrin, for example. Their ingredients fulfil three specific functions:
- Rehydration: Mineral salts help retain water and facilitate fluid absorption, counteracting fluid and salt losses through sweat during exercise.
- Energy: Carbohydrate-containing drinks provide quick energy, maintaining endurance and helping prevent fatigue during prolonged activity.
- Electrolyte balance: These minerals are essential for nerve signalling and muscle contraction. Replacing electrolytes lost through sweat prevents imbalances affecting performance and health.
When Should You Drink Isotonic Drinks?
Isotonic drinks are most useful during exercise, but are not always needed during training. Exercise intensity, duration and type, environmental conditions and individual needs determine whether to include them.
Simply put, significant fluid and electrolyte losses may make them worth trying. Your body may also signal a need through cramps, indicating excessive mineral loss is beginning.
In moderate-to-high-intensity endurance sports, especially lasting more than 1h, sweating is common and isotonic drinks may be recommended. If extra energy is useful, choose carbohydrate-containing versions.
In contrast, strength sports do not always call for them, as sweating need not be as high. Hot weather or individual characteristics can nevertheless increase sweating enough to make them useful.
We mostly hear about drinking them during training, but that is not always the only option. When is best for your circumstances?
Before Training
Drinking isotonic drinks before exercise is not common or necessary, since water usually provides adequate everyday hydration. If a demanding session is approaching, a small amount 30 minutes beforehand may help build reserves.
They can also be used as a competition strategy to start with appropriate blood electrolyte levels, helping water remain in the muscles rather than being expelled.
During Training
This is the most common time to consume an isotonic drink. Generally, unless conditions are very hot and humid, it is not needed for sessions under 1h unless the effort is very intense. Beyond an hour, drinking it to maintain electrolyte balance is key even without thirst. Take some approximately every 20 minutes, aiming for 500 to 1000 ml per hour, according to your needs.
After Training
After exercise, replacing lost fluids is advisable, and an isotonic drink can fulfil this role. Whether it contains carbohydrates depends on your goals and sport, and it can also function as a good recovery drink.
To determine an appropriate amount, weigh yourself before and after training. Dehydration usually reduces weight, although this also depends on intake during exercise. Use the result to adjust intake, remembering to drink 1.5 ml of isotonic drink per gram of weight lost. For example, dropping from 75 kg to 74.6 kg means a 400-gram difference. Calculate 400 grams lost x 1.5 of isotonic drink: 600 ml replaces the losses.
When Should You Avoid Isotonic Drinks?
Sodium is essential to their mineral composition. This matters when lost through sweating, but some situations require particular caution before recommending them.
Be cautious with conditions such as heart disease, hypertension or kidney problems. Their generally significant sodium content could adversely affect these conditions if extra sodium is unnecessary.
Isotonic drinks restore electrolyte balance, but generally, if exercise intensity or sweating has not been high, the body needs only water to regulate itself.
Without prolonged, demanding exercise, water is our best ally.
How Do You Choose a Good Isotonic Drink?
Everyone has different needs and goals, but these guidelines can help you choose.
Start with the essentials: electrolyte quality and quantity. The three key label minerals are sodium, potassium and chloride, in that order of quantity. Typically, a drink contains 500-700 milligrams of sodium per 100 grams, 200-300 mg of potassium / 100 g, and 200-100 mg of chloride / 100 g. Some also contain magnesium or zinc, at 30-10 mg / 100 g.
Depending on individual characteristics, such as sweat rate, exercise intensity and duration, and environmental conditions, the required amount might be half a litre or three times that.
The second common ingredient is simple carbohydrates. As discussed, these need not be present, as you can add them separately through favourite gels or bars, or some athletes may omit them if endurance is not the main goal.
If you want everything in one product, however, the drink should contain more than one carbohydrate type with different absorption speeds. With only simple carbohydrates, absorption may become saturated or produce an energy spike followed by a rapid drop. A practical combination includes glucose, maltose, fructose or sucrose alongside starches, maltodextrin, dextrose or glucose polymers.
The drink should also suit your tastes. A flavour you enjoy encourages consistent use and makes training more pleasant.
How Do You Prepare a Homemade Isotonic Drink?
If commercial drinks do not suit you, or making one is more economical, homemade preparation is an alternative worth considering.
There are ready-made powdered mixes and individual minerals or carbohydrates for those with more expertise.
These let you mix the required scoops in a bottle with the water amount planned for your activity, ready for action.
