When should you start refueling during swimming sessions, and what should you refuel with? Elite sports nutritionist James Collins answers all your questions about poolside nutrition.


If you are training to swim competitively, longer swims may require you to fuel during your session. If you're a recreational swimmer it's unlikely you'll have to worry about eating during a swim, though you might want to consider hydration.

Next, discover what to eat before a swim and after a swim as well as the best exercise to burn fat, top tips on staying hydrated and how much protein you need to build muscle.

What about refuelling during a swim?

Woman drinking a sports drink

As it's difficult to eat during a swim, the focus should be on fuelling before training to maintain your energy. For endurance training (over an hour) or high-intensity sessions, taking on small amounts of carbs may help to maintain performance. The focus of these should be around carbohydrate-electrolyte sports drinks (or gels), which are rapidly absorbed in the gut.

New research shows that even taking on small amounts of a carb-based sports drink or using it as a mouth rinse, helps to activate the brain and potentially improve motivation - this may be a useful strategy for later in your swim, when you can’t face taking on too much. As the response is very individual, if you choose to use these products be sure to practice this strategy during training.

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How do I stay hydrated?

Staying hydrated is an important consideration when swimming, as often temperatures in the pool and out are warm and humid. This makes sweat loss (and overall hydration status) difficult to determine, as swimmers are already wet from the pool. However, you should bear in mind that if you lose as much as 2% or more of your body mass (e.g. 1kg for a 50kg athlete) through fluid loss, this may negatively affect performance and concentration, and put additional strain on your body making training feel harder.

Regular swimmers should try to estimate their sweat rates. This is easily done by weighing yourself (in minimal clothing) before and after a swim (following towelling down), then subtracting any fluid consumed. Every 1 kg lost = 1 litre in sweat (e.g. 1 litre lost from a 120minute swim). For every 1kg lost:1.5litres of fluid needs to be replaced (to allow for continued losses post session). A basic rehydration strategy may then be developed to replace fluid losses after training.
Don’t forget to listen to your body, and drink according to your thirst. The body’s physiology is tightly regulated so when there is excess sweat loss (affecting blood levels) the thirst mechanism is triggered.
Together these measures should help exercisers develop an appropriate strategy to stay hydrated, given one size doesn’t fit all.

How often should I drink during my swim?

Woman lane swimming

Before your training session drink 500ml of water, about two hours before getting in the pool. This will allow any excess to be passed as urine. Then, if tolerated, take small sips over the course of the session to help keep levels topped up.
A small amount of dehydration isn’t a problem, the body can tolerate this – which means rehydrating during your swim may only be necessary if you complete a long or particularly heavy training session.

What are electrolytes and where can I get them?

Electrolytes are found in the blood, sweat and other fluids and have an important role to play in maintaining fluid balance within the body. Sodium is the most important electrolyte for hydration while others include potassium and chloride. Electrolyte levels are tightly controlled by the body, but may, along-with fluid, be lost in sweat and therefore need to be replaced.

Drinking large volumes of water on its own may just pass straight through the intestines and be lost as urine but by incorporating electrolytes your body will be able to absorb and retain the fluid, thus maintaining hydration.
Electrolytes are found naturally in food, and are also found in sports drinks and gels, which are an easy way to absorb and retain fluid during training.

Can I continue to drink caffeine and alcohol in moderation during my training?

Espresso being poured from a machine

It’s better to cut out (or cut down) alcohol around heavy training sessions, as this may interfere with the body’s maintenance of blood glucose and recovery (including sleep quality) after training. If you are going to enjoy the odd tipple, have it after your post-training recovery.
After a lot of bad press, research suggests some caffeine, taken at the appropriate times, may actually be a positive inclusion for performance. If you are a regular tea or coffee drinker, these drinks will contribute to your daily fluid intake and in smaller amounts don’t dehydrate, as we had previously thought.

The stimulatory effect of caffeine is often employed by elite swimmers to help make training feel easier.

Now you know what to eat and drink during your swim, get the rest of your training nutrition right:

What to eat before your cycle
What to eat during your cycle
What to eat after your cycle
What to eat before your swim
What to eat after your swim
What to eat before your run
What to eat during your run
What to eat after your run

This page was reviewed on 8 March 2024 by Kerry Torrens


As a sport and exercise nutritionist, James Collins regularly provides comment and consultation within the media and maintains a role of governance within health & nutrition in the UK, where he sits on The Royal Society of Medicine's (RSM) 'Food and Health' Council. He was heavily involved in advising Team GB in the run up to the London 2012 Olympic games, and now towards Rio 2016.

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