Water weight for athletes: carbs, salt and sweat
Hybrid athletes see bigger overnight swings on the scale than people who only diet. Most of it is water, and most of that water follows carbohydrate and sodium rather than sweat.
Water weight is the part of body mass that changes with stored glycogen, sodium balance, gut content and fluid intake rather than with fat or muscle tissue. For an athlete it routinely moves the morning scale by 0.5 to 1.5 kg (1 to 3 lb) between two days. Fat tissue, even in an aggressive deficit, changes by roughly 0.1 kg (0.2 lb) a day. A single morning on the scale is therefore mostly a reading of water.
Glycogen: the biggest lever
Muscle and liver store carbohydrate as glycogen, and glycogen is stored with water. The classic estimate, from Olsson and Saltin in 1970, is 3 to 4 g of water per gram of glycogen. A 2015 study in trained cyclists by Fernández-Elías and colleagues measured a much wider range inside muscle, from about 3 g up to 17 g of water per gram, depending on how glycogen and fluids were restored after exercise in the heat. A 2023 narrative review in Nutrients summarises the field the same way: the relationship is positive and real, the exact ratio varies.
The practical consequence is large. An athlete who eats 150 g (5 oz) more carbohydrate than usual the day before a key session can store several hundred grams of extra water with it. Carb loading for a race is expected to add 1 to 2 kg (2 to 4 lb) for the same reason. That weight is fuel. Cutting it to make the scale look better removes the thing that makes long efforts possible.
The size of the effect is individual. One published N=1 prediction log that refits its own coefficients every morning found the carb effect for its athlete close to zero after a week, against a textbook starting value of 0.3 kg per 100 g. A week is far too short to generalise from. It does show why a fixed rule of thumb misleads some athletes.
Sodium: the short-term holder
The body keeps blood sodium concentration in a narrow band. A salty meal is followed by thirst and reduced urine output until the extra sodium is excreted, and the water held in the meantime shows on the scale. The effect is usually a few hundred grams and fades within one to three days. Restaurant meals, recovery foods, electrolyte drinks and salt tablets all count. Weekend eating patterns, which tend to be saltier and higher in carbohydrate, are one reason weight rises from Friday to Monday in large datasets (Orsama et al., 2014, found weight rising over weekends and falling during the week).
Sweat: the swing that evens out
A long session in heat can take 1 to 3 kg (2 to 7 lb) of sweat. Weighed straight after training, that loss is real. Weighed the next morning, after the athlete has eaten and drunk normally, most of it is gone. Thirst and kidney regulation restore body water within about a day for anyone drinking to need. That is why sweat is the weakest predictor of next-morning weight of the four effects here, provided fluids are replaced.
The exception is deliberate under-drinking, which some athletes do before weigh-ins. It shows up as a lower number and a worse session.
Creatine: water that stays in the muscle
Creatine monohydrate draws water into muscle cells. Powers and colleagues (2003) found total body water increased with supplementation without changing the ratio of intracellular to extracellular water. A loading phase of about 20 g a day commonly adds 1 to 2 kg (2 to 4 lb) within a week. A steady 3 to 5 g a day reaches a similar level more slowly. For athletes this water is part of the intended effect, and it stays as long as supplementation continues. The site’s creatine evidence review covers dosing.
How big is each effect?
| Driver | Typical size on the morning scale | Lasts |
|---|---|---|
| Carbohydrate above usual (glycogen) | up to ~0.5 kg (1 lb) per day, 1 to 2 kg (2 to 4 lb) when carb loading | until glycogen is used |
| Sodium above usual | 0.1 to 0.5 kg (0.2 to 1 lb) | 1 to 3 days |
| Food still in the gut | 0.5 to 1.5 kg (1 to 3 lb) | until the next bowel movement |
| Sweat, replaced | close to zero | hours |
| Creatine (loading) | 1 to 2 kg (2 to 4 lb) | while supplementing |
| Fat tissue | about 0.1 kg (0.2 lb) a day in a solid deficit | permanent |
The ranges are editorial summaries of the sources above and typical athlete logs, not measured constants. Individual responses differ by a factor of two or more.
Reading the scale with water in mind
- Weigh under fixed conditions. On waking, fasted, after the toilet, same scale. This removes gut content and fluid intake as variables.
- Judge a 7 to 10 day trend. An exponentially weighted average in which each new reading counts about a quarter reacts within a week and ignores single spikes.
- Explain the day before. A high-carb or salty day predicts a heavier morning. If the cause is known, the jump is not a gain.
- Never “cut water” before a key session. The weight returns within days, the glycogen does not refill in time.
A trend-and-adjustment approach can be taken one step further by predicting the next morning’s weight from the trend plus the previous day’s carbs, sodium and energy balance, and scoring the prediction against the scale. A public example of such a self-scoring log is linked in the sources. Telling water from a real stall is covered in weight loss plateau or water?
FAQ
- How much water weight can an athlete gain or lose in a day?
- Commonly 0.5 to 1.5 kg (1 to 3 lb) between two mornings, and more around carb loading, long sessions in heat or a salty meal. Fat tissue changes by roughly 0.1 kg (0.2 lb) a day at most during a solid deficit, so a larger overnight swing is almost entirely water, glycogen and gut content.
- Does sweating make you lose weight?
- It lowers the scale for a few hours, then the loss comes back as you drink. Sweat is water and electrolytes, not fat. An athlete who replaces fluids after training weighs about the same the next morning whether the session was hot or cool.
- Does creatine cause water retention?
- Yes, mostly inside the muscle. A loading phase commonly adds about 1 to 2 kg (2 to 4 lb) within the first week, and a 3 to 5 g daily dose without loading adds less over several weeks. It is intracellular water, not bloating under the skin.
- How do you get rid of water weight quickly?
- Eat your usual amount of carbohydrate and salt again after a high day, keep drinking normally, and wait two to three days. Cutting carbs or water sharply sheds weight fast but empties glycogen, which is the fuel endurance and HYROX performance depend on.