In 30 seconds
- Replace between 125 and 150% of what you have lost: about 1.25-1.5 litres for every kilo that comes off on the scales.
- Plain water, in large amounts, is quickly passed as urine. With sodium, in your food or in your drink, you retain more fluid.
- In a study with 72 people, whole milk, skimmed milk and oral rehydration solution were retained better than water.
- If you have lost less than 5% of your body weight and are not training again within 24 hours, your meals and water are enough.
Drink a little more than you have sweated: between 1.25 and 1.5 litres for every kilo of body weight lost, in sips over the following hours. And have some sodium with it, in your food or in a drink with electrolytes: that way the fluid stays in your body instead of passing straight through.
Step by step
Rehydrate using the scales as your guide
First, measure what you have lost
The scales are the simplest way to find out. Weigh yourself before and after training, in minimal clothing and after drying off your sweat well: for practical purposes, each kilo lost is equivalent to a litre of fluid.
If you do not know how much you sweat, we explain it step by step in how to calculate your sweat rate, or you can use the hydration calculator.
Of the fluid you have lost
Drink more than you have lost: between 125 and 150%
How much to drink: more than you lose
The joint recommendation of the US and Canadian nutrition and sports medicine bodies is to replace between 125 and 150% of the fluid lost, with water and sodium 1. The German Nutrition Society gives the same practical figure: 1.5 litres per kilo 2.
| Weight lost | Drink over the following hours |
|---|---|
| 0.5 kg | 0.6-0.75 L |
| 1 kg | 1.25-1.5 L |
| 1.5 kg | 1.9-2.25 L |
| 2 kg | 2.5-3 L |
Calculated at 125-150% of the fluid lost (Thomas et al., 2016). Drink it in sips and with a little sodium.
Why more than 100%? Because your body keeps losing fluid as urine while you rehydrate. If you only replace what you have sweated, a few hours later you are short again 4 5.
In sips, not all at once
Drinking a litre of water in five minutes seems effective, but it is not. Large volumes of plain water quench your thirst and make you pass more urine, so a good part of it is lost 4.
What works is drinking little by little, spread over the hours after training 2. Keep your glass or bottle to hand and keep sipping while you shower, have dinner or rest.
Make the fluid stay
A litre all at once, or little by little with sodium
Sodium makes the water stay
Sodium is the electrolyte you lose most when you sweat, and it is also the one that helps you retain the fluid you drink. It keeps water in the blood and reduces the amount that leaves as urine 5 6.
For rapid rehydration, the classic studies point to drinks with plenty of sodium, “perhaps as high as 50-60 mmol per litre”, that is, between 1,150 and 1,380 mg 4. That is more than most sports drinks contain, which is why food matters so much.
If you eat when you finish, there is no need to overcomplicate things: when there is food, it makes no difference whether you drink water or a sports drink, because the food provides the sodium 6. A plate with a little salt and some water is a perfectly good way to rehydrate.
What to drink
In a study with 72 people that compared 13 everyday drinks, a litre of each, only three were clearly retained better than water: oral rehydration solution, whole milk and skimmed milk 3. The milks also provide protein and carbohydrates.
| Option | When it fits |
|---|---|
| Water with a salty meal | The simplest option if you are in no hurry. The food provides the sodium. |
| Milk (whole or skimmed) | Retained better than water, and it also provides protein and carbohydrates. |
| Drink with electrolytes | If you are going to train again soon, or you have sweated a lot and are not eating yet. |
| Diluted juice | One part juice to two parts still mineral water with sodium. |
| Oral rehydration solution | Very large losses or gastroenteritis; in that case, check with your doctor. |
Sources: Maughan et al., 2016; Mosler et al., 2020; McCubbin et al., 2020.
The German Nutrition Society suggests a simple mix: one part fruit juice to two parts still mineral water rich in sodium 2. If you want to know which minerals you replace with each option, you will find it in electrolytes: what they are and when to take them.
Carbohydrates and protein help too
It is not only sodium: the carbohydrates and protein in your drink or food also help water to be absorbed and stay in the body 5 6.
Are you training again in less than 8 hours? Then you also need to restore energy quickly. The recommendation is to take 1-1.2 g of carbohydrate per kilo per hour for the first 4 hours 1. If you have less than 4 hours, the International Society of Sports Nutrition suggests about 1.2 g per kilo per hour. Another option is to combine 0.8 g of carbohydrate with 0.2-0.4 g of protein per kilo per hour 7.
When do you need to hurry?
Not always. If you have lost less than 5% of your body weight and are not going to train in the next 24 hours, your normal meals and water are enough 2.
It is worth following a plan when:
- You train twice on the same day or compete the next day, as in a padel or football tournament.
- You have lost more than 2% of your body weight, for example in the heat or on a long outing 1.
- You feel very thirsty or tired, or your urine is dark.
How to tell you are back to normal
Two simple signs: your weight returns to what it was before training and your urine is pale yellow 2. If it is still dark, you still need more fluid.
Do not overdo it either
More is not better. Hyponatraemia, a fall in blood sodium from drinking too much, can occur during exercise and also up to 24 hours afterwards 8. Drink what you need, not huge amounts “just in case”. We cover it in drinking too much water during exercise.
Nitrus for rehydrating
When you finish a long session or one in the heat, make up a serving of Nitrus Isotonic in 400-500 ml of water. It gives you about 195 mg of sodium, 148 mg of potassium and 15 g of carbohydrates, along with all 13 vitamins. Riboflavin (vitamin B2), vitamins B6, B12 and C, niacin, pantothenic acid and folate contribute to the reduction of tiredness and fatigue. A varied and balanced diet and a healthy lifestyle are important.
Have it with a meal that contains a little salt and the rest of the water you need according to the table.
Frequently asked questions
How much water should you drink after training?
Between 1.25 and 1.5 litres for every kilo of body weight you have lost, spread out in sips over the following hours. You drink a little more than you have sweated because you will keep losing fluid as urine.
Is water or an isotonic drink better for rehydrating?
If you are going to eat soon, water with a meal that contains a little salt works just as well. If you are not going to eat, or you are training again within a few hours, a drink with sodium helps you retain the fluid better.
Is milk good for rehydrating after exercise?
Yes. In a study with 72 people, whole and skimmed milk were retained in the body better than water, as was oral rehydration solution. It also provides protein and carbohydrates.
How do I know if I have rehydrated?
Your weight returns to what it was before training and your urine is pale yellow. If it is still dark, you still need more fluid.
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. View publication
- Mosler S, Braun H, Carlsohn A, et al. Position of the working group sports nutrition of the German Nutrition Society (DGE): fluid replacement in sports. Dtsch Z Sportmed. 2020;71(7-9):178-184. View publication
- Maughan RJ, Watson P, Cordery PA, et al. A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. Am J Clin Nutr. 2016;103(3):717-723. View publication
- Maughan RJ, Leiper JB, Shirreffs SM. Factors influencing the restoration of fluid and electrolyte balance after exercise in the heat. Br J Sports Med. 1997;31(3):175-182. View publication
- Evans GH, James LJ, Shirreffs SM, Maughan RJ. Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration. J Appl Physiol. 2017;122(4):945-951. View publication
- McCubbin AJ, Allanson BA, Caldwell Odgers JN, et al. Sports Dietitians Australia position statement: nutrition for exercise in hot environments. Int J Sport Nutr Exerc Metab. 2020;30(1):83-98. View publication
- Kerksick CM, Arent S, Schoenfeld BJ, et al. International Society of Sports Nutrition position stand: nutrient timing. J Int Soc Sports Nutr. 2017;14:33. View publication
- Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Br J Sports Med. 2015;49(22):1432-1446. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product.
