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What is water weight and how do you lose it?
Water weight is extra fluid in your body, not fat. It can move the scale by 1 to 2 kg (2 to 4 lb) in a day or two, and it comes from salt, carbohydrate, hormones, a hard workout, heat or alcohol. The safe way to lose it is to fix the cause: less salt, steady carbs, enough water, sleep and movement. It also explains the fast first week of a diet: a woman of 70 kg (154 lb) in a steady deficit loses about 0.35 kg (0.8 lb) of fat in week 1, but the scale may show 1.4–2.4 kg because stored carbohydrate drags water with it.
What is water weight?
Your body is roughly half to two-thirds water, and the amount you hold changes by a kilo or two from day to day. "Water weight" means the part of that swing that sits in your tissues or around cells: it isn't fat, it comes and goes, and it can hide fat loss (or fake fat gain) on the scale. For why the scale moves by itself: why your weight fluctuates.
How much water weight can you hold or lose?
For most adults, 1 to 2 kg (2 to 4 lb) is the normal day-to-day range, and 2 to 3 kg in a rough week (a big salty meal, a flight, a period, a first hard workout). Larger, lasting swelling is not "water weight" in this sense: see the doctor section below.
Carbohydrate is the biggest lever. Your muscles store carbohydrate as glycogen, roughly 400–500 g in muscle and about 100 g in the liver. Each gram of glycogen is stored with about 3 to 4 g of water (Kreitzman et al., 1992; the table below uses 3 g to stay conservative). So when you eat fewer carbs or calories and the stores run down, you lose the glycogen and its water together. Using up 250–500 g of glycogen is worth 1.0–2.0 kg on the scale.
Why does the first week of a diet drop so fast?
| Person | Fat lost | Water + glycogen | Scale could show |
|---|---|---|---|
| Woman, 70 kg 154 lbeats 1,450 | 0.35 kg | 1.0–2.0 kg | 1.4–2.4 kg |
| Woman, 85 kg 187 lbeats 1,580 | 0.42 kg | 1.0–2.0 kg | 1.4–2.4 kg |
| Man, 90 kg 198 lbeats 1,950 | 0.45 kg | 1.0–2.0 kg | 1.4–2.5 kg |
That's why week 1 feels amazing and week 2 feels slow. Both are normal. The real pace is the fat column, which is what the box above calculates. Plan for it and don't read week 1 as your pace (how much weight to lose per week, how much you can lose in a month).
What causes water weight?
- Salt. Sodium holds water. A salty restaurant meal can add a kilo by next morning.
- Carbohydrate. More carbs mean more glycogen and more water; fewer carbs the reverse. This is also why low-carb diets drop fast at first (how many carbs to lose weight).
- Hormones. The days around your period often add 0.5 to 2 kg: weight gain on your period.
- A new or hard workout. Sore muscles hold fluid while they repair, so you may weigh more for a few days after starting to train or after a big session.
- Heat, flights and sitting. Warm weather, long travel and long days sitting let fluid pool in the legs.
- Alcohol. It dehydrates at first and rebounds with water retention, plus the calories.
- Some medicines, including steroids and some blood pressure and diabetes drugs, can cause swelling. Never stop a medicine on your own.
How do you know it's water, not fat?
- It appears or vanishes within a day or two. Fat doesn't.
- It follows a cause: salty food, carbs, your period, a hard workout, a flight.
- Your clothes fit the same or your rings feel tight but your waist hasn't changed.
- Weight is up more than the calories could explain. A kilo of fat takes 7,700 extra calories (the 3,500-calorie rule); you didn't eat that.
Check your trend over 3–4 weeks instead of a single day. If the trend is flat while you believe you're in a deficit, see calorie deficit but not losing weight and weight-loss plateau.
How to lose water weight safely
- Eat a normal, steady amount of salt. Cut very salty processed food and takeaway; don't cut salt to zero.
- Don't swing your carbs. Steady carbs keep glycogen and its water steady. Refined carbs and sweets in large amounts add the most.
- Drink normally. Cutting back on water doesn't shift water weight and leaves you thirsty and tired.
- Eat potassium-rich foods such as bananas, potatoes, beans, yoghurt, leafy greens, and enough magnesium.
- Sleep 7–9 hours. Poor sleep raises stress hormones that hold water.
- Move. Walking daily helps fluid return from the legs (how many steps a day).
Expect it to take a few days to a week, not hours.
What not to do
- Diuretics and "water pills". They can drop electrolytes and cause cramps, dizziness or heart rhythm problems.
- Saunas and sweat suits. Sweating is water you drink back within hours; it can also cause heat illness.
- Drastic dehydration (the weigh-in trick). It is dangerous and doesn't change fat.
- Zero-carb or zero-salt crash plans to drop weight before an event. They rebound.
How long does water weight take to go?
After a salty meal or flight: 1–3 days. After your period starts: about a week. After a hard new workout: 3–7 days. After a long stretch of high carbs or alcohol: a week or two of normal eating. The fat you're losing doesn't wait on any of this.
When is swelling medical?
See a doctor promptly if swelling is in one leg only or one leg is red, warm or painful (a blood clot is possible). Seek urgent help for sudden shortness of breath or chest pain. See a doctor soon if you have swelling that doesn't go down, puffiness in the face or around the eyes, weight up more than 2 kg in a week, or swelling with tiredness or less urine. Heart, kidney, liver and thyroid problems can all cause fluid retention.
Sources
- Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. Am J Clin Nutr 1992;56(1 Suppl):292S–293S.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet 2011;378(9793):826–837.