The scale jumped
overnight. That's water,
not fat.
A 1 to 2kg jump in a day is almost always water, driven by salt and carbs, not fat you've gained. Here's why, how to shift it in a day or two, and when to see your GP.
Free download Tracks salt vs the NHS 6g cap iPhone
Why did I gain
weight overnight?
You can't gain a kilo of fat in a day, that would take roughly 7,700 surplus calories. What moved is water, and two things on your plate pull it in.
Salt holds water
Sodium makes your body hold extra water to keep blood concentration steady. A salty takeaway, a tin of soup or a sharing bag of crisps can park 1 to 2kg of water for a day or two. The NHS caps adults at 6g of salt a day, and most of us are over it.
Carbs hold water too
Your body stores carbohydrate as glycogen, about 500g of it across muscle and liver, and each gram drags roughly 3g of water along, so around 1.5kg of water is tied up in your carb stores. A big pasta or rice meal, or refilling after a low-carb stretch, tops it right back up.
And the usual suspects
Hormonal shifts in the days before a period, a poor night's sleep, a long flight, a hard workout, or simply being too hot all nudge water retention up. None of it is fat.
Water weight
vs real fat.
The tell is speed. Fat changes slowly; water changes by the hour.
Your weight swings 1 to 2kg across a normal day from food, drink, salt and the toilet, well before any fat has changed. Real fat loss is slow: a kilo of fat is about 7,700 calories, so it takes a sustained deficit over a week or more, not a morning.
So a number that spikes after a salty meal or a carb-heavy weekend, then settles a day or two later, was water the whole time. The fix isn't panic, it's understanding what moved it.
How do I lose
water weight?
Six things that work, ranked fastest first. No detox teas, no diuretic pills. The big one is carbs.
The fastest lever is cutting carbs. Your body keeps roughly 500g of glycogen in your muscles and liver, and each gram drags about 3g of water with it, so that's around 1.5kg of water tied up in your carb stores. Drop your carbs toward 50 to 100g a day for a few days and the body burns that glycogen off, releasing the water with it. It's why low-carb diets show a dramatic first week, and why up to 70% of the weight you lose in the first few days of any diet is water and glycogen, not fat.
One honest caveat: this is water, not fat. Eat normal carbs again and your glycogen, and its water, refills. It's a fast way to debloat for an event, not a shortcut to fat loss.
1. Cut the carbs
The surefire one. Toward 50 to 100g a day for a few days empties the glycogen that's holding ~1.5kg of water. Cut refined carbs first: white bread, pasta, rice, sugary drinks and snacks.
2. Cut the salt
Aim under the NHS 6g-a-day cap (about 2.4g sodium). Most of it hides in bread, sauces, ready meals and deli meat, not the salt cellar. As sodium falls, the water it held follows within a day or two.
3. Drink more, not less
Counterintuitive but real: under-drinking makes your body cling to water. Steady water through the day, roughly 6 to 8 glasses, tells it to let go.
4. Top up potassium
Potassium balances out sodium and helps you shed the water it holds. Leafy greens, potatoes, beans, bananas and tomatoes are easy sources, no supplement needed.
5. Move and sweat
A workout burns glycogen, frees its water, and you lose fluid through sweat and breath. Even a brisk walk shifts fluid that's been pooling if you've been sat still.
6. Sleep, skip the nightcap
Poor sleep raises the stress hormones that hold water, and alcohol triggers a rebound where you retain more the next day. A good night and a dry evening both help it settle. Magnesium (about 200mg a day) can ease premenstrual water retention, but give it a cycle or two.
How fast does
it come off?
Faster than fat, which is the whole point.
Most salt- or carb-driven water weight settles in 24 to 48 hours once the cause eases, often a kilo or more. It's why a Monday weigh-in after a salty weekend reads high and a midweek one reads normal, with nothing else changed.
If you're tracking weight loss, weigh at the same time each day and watch the weekly trend, not the daily number. The day-to-day wobble is mostly water, and reading it as fat will drive you mad.
When to see
a doctor.
Everyday water retention is normal. Some swelling isn't, and that's a GP conversation, not a diet one.
See your GP if swelling is persistent, only on one side, leaves a dent when you press it, or comes with breathlessness, chest pain or a sudden large gain over a few days. The NHS lists these as signs that fluid retention may need checking, because it can point to a heart, kidney or other condition. NutraSafe is a tracking tool, not a diagnosis, so take anything that doesn't settle to a doctor.
Track the two
things that cause it.
Water weight is salt and carbs. NutraSafe reads both straight off the UK label, so you can see which one spiked.
Your salt, vs the 6g cap
Scan a UK barcode and we pull the salt figure off the label and total your day against the NHS 6g adult cap, so you can spot the soup, sauce or ready meal that's parking the water.
Your carbs, day by day
The diary totals carbs from every food you log, so a high-carb day that topped up glycogen and its water is easy to see next to the scale.
The trend, not the wobble
Log your weight and the diary shows the weekly trend, so you read fat loss properly and ignore the daily water noise.
Frequently
asked.
Sourced to the NHS and standard physiology.
Yes. Salt- or carb-driven water weight usually settles within 24 to 48 hours once the cause eases. It isn't fat, and you don't need to do anything drastic to lose it.
Yes. Sodium makes your body hold extra water to keep blood concentration steady, so a salty meal can add 1 to 2kg of water for a day or two. The NHS caps adults at 6g of salt a day.
They can. Carbohydrate is stored as glycogen, and each gram of glycogen holds about 3g of water. A big carb meal, or refilling glycogen after low-carb eating, brings water with it. It's the reason low-carb diets show a fast first-week drop that is mostly water.
Yes, oddly. Under-drinking makes your body hold on to more water. Drinking steadily through the day helps it release what it's retaining.
Commonly 1 to 2kg over a day or two, sometimes more after a very salty or carb-heavy stretch. It varies by person, diet and activity. If swelling is persistent or one-sided, see your GP rather than treating it as water weight.
See your salt and carbs,
read the weekly trend,
stop fearing the daily number.
Free download. Scan UK barcodes for salt and carbs, log your weight and read the trend. Up to 25 logs a day on the free tier; Pro £3.99/month or £34.99/year.
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