You can eat
- Water, day to day and during training sessions lasting less than an hour.
- Isotonic drink, during sessions or matches lasting more than 75 minutes and on very hot days.
- Homemade isotonic drink, using the recipe below.
- Hypotonic drink, when it is very hot and replacing fluid is the priority.
- Ripe fruit, such as a banana or orange, with water during breaks in moderate training.
- Dried apricots or raisins with water during long efforts, if you are comfortable chewing.
- Skimmed milk or soy drink after finishing, which provides fluid, carbohydrates, protein and some sodium.
What to avoid
- Energy drinks with lots of caffeine, which are not designed for hydration
- Fizzy, sugary soft drinks during exercise, because the bubbles fill your stomach.
- Undiluted hypertonic drinks with more than 8% sugar, which can cause nausea during exertion.
- Drinking more water than you lose through sweat during events lasting more than two or three hours.
- Soft drinks marketed for replenishment that contain less than 200 mg of sodium per litre.
- Alcohol after training or competition, because it slows glycogen recovery and worsens sleep.
- Drinks with added supplements, which increase the cost without improving hydration.
Changes that help
During exercise
Instead of a fizzy soft drink during breaks, have a cool, non-carbonated isotonic drink, because bubbles fill your stomach and soft drinks contain very little sodium.
If you want to spend less
Instead of commercial sachets with colourings, make the homemade isotonic drink the evening before: it costs very little and provides similar amounts of carbohydrates and sodium.
After training
Instead of a commercial recovery shake, have milk or a soy drink with cocoa and a banana, which provides fluid, carbohydrates and protein for less money.
Habits that help
- Weigh yourself before and after a hard training session. Each kilogram lost is roughly one litre of sweat to replace [2].
- Sip every 15 or 20 minutes instead of drinking half a litre at once.
- Start hydrated. Drink 5 to 10 ml per kilogram of body weight in the 2 to 4 hours beforehand [1].
- Check the colour of your urine. Pale yellow is a good sign; dark urine may mean you need more fluid [2].
- Keep your bottle cool, but not ice-cold, as it is more appealing and you are more likely to drink what you need.
Staying hydrated seems easy. You drink when you are thirsty or buy the brightly coloured bottle at the supermarket. In consultations, we often see dips in performance and stomach discomfort that are linked to what is in the bottle.
Water is the everyday foundation. When the effort goes on for longer or the heat rises, it may not be enough. Drinking more water without replacing salt can also cause problems.
What is a sports drink for, and how is it different from water?
A well-formulated sports drink does three things at once. It replaces the water you lose through sweat, provides quick energy in the form of carbohydrates, and replenishes the sodium lost in sweat [1].
Water replaces fluid, but provides no energy or salts. During moderate efforts lasting less than an hour, it is exactly what you need. As activity goes on, muscle glycogen (the muscle’s carbohydrate stores) is used up and sodium losses build up.
During prolonged exercise, a drink containing carbohydrates and sodium maintains performance better and rehydrates better than water alone [1]. To see how a drink fits with the rest of your diet, read our sports nutrition guide.
What is the difference between hypotonic, isotonic and hypertonic drinks?
The difference lies in osmolality, meaning how many dissolved particles the drink contains compared with blood.
A hypotonic drink contains fewer particles than blood, with little sugar and few salts. Water is the extreme example. It is absorbed quickly and can be suitable when the heat is intense and hydration is more urgent than energy intake.
An isotonic drink has a concentration similar to blood, between 200 and 330 mOsm/kg according to the European Food Safety Authority (EFSA) [3]. It balances water absorption with energy intake.
A hypertonic drink is more concentrated than blood. Examples include undiluted juice, sugary soft drinks and gels taken without water. They leave the stomach more slowly and draw water into the intestine to dilute them. During exertion, they can cause nausea, abdominal pain or diarrhoea.
When do you need an isotonic drink, and when is water enough?
It depends on how long and intense the effort is, and how hot it is. The dietetic associations of the United States and Canada and the American College of Sports Medicine divide it into time ranges [1].
- Less than 45 minutes. No carbohydrates or salts are needed during exercise; water is enough [1].
- 45 to 75 minutes at high intensity. Small amounts of carbohydrates are enough, or even rinsing your mouth with a carbohydrate-containing drink [1].
- 1 to 2.5 hours. 30 to 60 g of carbohydrates per hour [1], which can be supplied by sipping an isotonic drink.
- More than 2.5 or 3 hours. Up to 90 g per hour, combining different sugars, and only if you have trained your digestive tolerance beforehand [1].
In very hot weather, or if you sweat heavily, you may need sodium sooner. For long bike rides, our cycling diet guide explains how to plan your bottles and solid food.
What an effective isotonic drink contains
It contains two things in the right proportions: carbohydrates and sodium.
Carbohydrates should make up 6% to 8% of the mixture, that is, 60 to 80 g per litre [4]. Glucose, sucrose (table sugar) and maltodextrin all work. If you increase intake towards 90 g per hour for very long events, it is advisable to combine glucose and fructose [1].
Sodium is the salt most lost through sweat. EFSA specifies 460 to 1,150 mg per litre (20 to 50 mmol/L) for drinks that claim to improve water absorption and endurance performance [3]. Sodium helps maintain the desire to drink and helps retain the fluid you take in [2].
How to make a homemade isotonic drink
You do not need to buy a mix. You can make one litre in two minutes with ingredients from your kitchen.
- Pour one litre of water into a bottle
- Add 60 g of sugar, about four level tablespoons
- Add 1.5 g of salt, a quarter of a teaspoon
- Squeeze and strain the juice of one lemon or half an orange for flavour.
- Shake until the grains have dissolved and keep it in the fridge
It contains around 6% carbohydrates and about 590 mg of sodium per litre, within the ranges mentioned above [3]. Drink it within 24 hours.
Why are soft drinks not suitable as sports drinks?
People often have cola or another sugary drink during a ride or after a match, thinking it replaces what they have lost. It is not the best choice.
A sugary soft drink contains around 10-11% sugar, more than an isotonic drink, so it is hypertonic. It leaves the stomach more slowly and retains fluid in the intestine.
Its sodium content is usually very low, well below the minimum of 460 mg per litre for a replenishment drink [3]. The bubbles also fill your stomach and reduce your desire to drink what you need.
Energy drinks are different. They contain a lot of caffeine and other stimulants, can cause palpitations and stomach discomfort during exertion, and are not designed for hydration.
Is it dangerous to drink too much water while training?
During prolonged efforts, it can be. Drinking much more than you sweat out, especially plain water, can cause exercise-associated hyponatraemia. This is a drop in blood sodium below 135 mmol/L during exercise or in the following 24 hours, according to the Wilderness Medical Society guideline [5].
The same guideline says that drinking more than you lose is the main cause and recommends drinking to thirst rather than following a fixed volume [5]. Symptoms include nausea, headache and swelling of the hands and feet. In severe cases, confusion can occur; this is a medical emergency.
During prolonged efforts, drink in line with your sweat losses without overdoing it, and take sodium along with fluid [1].
What mistakes do we see most often in consultations?
Three come up every season.
- Taking only water on a long session. After about an hour and fifteen minutes, you may be short of carbohydrates and sodium, and feel it in the final kilometres.
- Buying isotonic drinks for an easy walk. They are not needed for short efforts, and each litre adds about 60 g of sugar.
- Trying a drink for the first time on race day. Practise what you will drink in competition beforehand, during long sessions at a similar pace.
Choose your drink according to the duration of the effort and the heat, not the colour of the bottle.
If you compete in endurance events, are unsure how much you sweat, or have stomach discomfort when drinking, our team of sports dietitians can work out a hydration plan with you, in Barcelona or online.
Your first step this week
Try your drink during a long training session
Make the homemade isotonic drink the evening before your next session lasting more than an hour, and note how it feels. That way, you will have tried it before race day.
When to see a doctor
When to see a doctor
We adjust energy intake, hydration, timing and recovery to help you perform and reduce the risk of injury. We do not diagnose injuries, assess your heart or treat eating disorders, which can be disguised as discipline in sport.
Arrange a medical appointment without waiting to change your diet if you notice any of these signs:
- You feel pain or tightness in your chest, become very dizzy, faint, or your heart races during exercise [6]
- During exercise in the heat, you feel confused or disoriented, or stop sweating [6]
- After a long event where you have drunk a lot of water, you feel nauseated, have a headache and notice swelling [5]
- Your urine is very dark, cola-coloured, and you have severe muscle pain after an unusual training session [6]
- You have stopped having periods, have had several stress fractures, or your performance has been declining for months and you feel very tired [7]
- You feel obliged to train fasted, are afraid of eating certain foods, or your diet controls your social life [7]
Chest pain, fainting, confusion in the heat or cola-coloured urine: seek emergency care today, or call 112 if you are competing. Missing periods, stress fractures or ongoing loss of performance: see your GP or a sports doctor this week, before changing your diet. If your relationship with food is the problem, seek specialist psychological support.
Hard training and eating enough go together. These signs nearly always appear when the latter falls behind.
Start with a first appointment
Tell us what sport you do and what you want to achieve. We will guide you on which dietitian and format —in person at one of our clinics or online— fit you best, and you can book when you are clear about it.
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Resource hubStrength and muscle mass: nutrition guides
Guides to organise your questions about food, strength training and recovery.
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Sources
- Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016;116(3):501-528. doi:10.1016/j.jand.2015.12.006
- Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377-390. doi:10.1249/mss.0b013e31802ca597
- EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific Opinion on the substantiation of health claims related to carbohydrate-electrolyte solutions and reduction in rated perceived exertion/effort during exercise, enhancement of water absorption during exercise, and maintenance of endurance performance. EFSA J. 2011;9(6):2211. doi:10.2903/j.efsa.2011.2211
- Kerksick CM, Wilborn CD, Roberts MD, et al. ISSN exercise & sports nutrition review update: research & recommendations. J Int Soc Sports Nutr. 2018;15(1):38. doi:10.1186/s12970-018-0242-y
- Bennett BL, Hew-Butler T, Rosner MH, et al. Wilderness Medical Society Clinical Practice Guidelines for the Management of Exercise-Associated Hyponatremia: 2019 Update. Wilderness Environ Med. 2020;31(1):50-62. doi:10.1016/j.wem.2019.11.003
- Roberts WO, Armstrong LE, Sawka MN, et al. ACSM Expert Consensus Statement on Exertional Heat Illness: Recognition, Management, and Return to Activity. Curr Sports Med Rep. 2023;22(4):134-149. doi:10.1249/JSR.0000000000001058
- Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee’s (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med. 2023;57(17):1073-1098. doi:10.1136/bjsports-2023-106994
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