Water weight is real, it moves fast, and it explains most of the dramatic scale changes you've ever seen. Here's how it works.
You step on the scale on Monday and it's down 1.5 kg from Friday. You step on it Thursday and it's back up 1 kg from Monday. Nothing dramatic happened in either direction — you ate roughly the same, exercised roughly the same, slept roughly the same.
What you're watching is water weight. It's the most misunderstood number in weight loss — and once you understand it, the scale becomes a lot less frightening.
Your body is roughly 55–65% water. For a 70 kg person, that's between 38 and 45 kg of water distributed throughout your blood, muscles, organs, and tissues. A 2% change in total body water — which is entirely normal and happens constantly — equals about 0.8 to 0.9 kg on the scale. A 5% change equals 2 kg.
None of that is fat. None of it reflects your diet working or not working. It's fluid moving in and out of your tissues in response to dozens of different signals your body is managing every hour of every day.
This is the part most people don't realise: water weight moves fast. The same mechanisms that bring it on reverse themselves quickly once the trigger is gone.
The pattern is consistent: water weight comes on quickly and leaves quickly. Fat, by contrast, takes weeks to accumulate meaningfully and weeks to lose. If you gained 1 kg overnight, it wasn't fat. If you lost 1 kg in two days, it probably wasn't fat either.
Any weight change under about a week is almost certainly water. Fat loss is slow, quiet, and only visible in trends measured over weeks — not days.
One specific cause of water weight deserves extra attention because it's so commonly misunderstood: carbohydrates and glycogen. When you eat carbohydrates, your body converts them to glycogen and stores it in your muscles and liver as a fuel reserve. The catch: each gram of glycogen is stored alongside 3–4 grams of water.
This means that eating a high-carb meal — pasta, rice, bread, pizza — can cause a meaningful overnight weight increase that is entirely glycogen and water. It means that cutting carbs dramatically (as many diets do initially) causes a rapid drop in scale weight that is mostly glycogen and water leaving the body, not fat. It's why low-carb diets produce dramatic first-week results that slow down sharply once the glycogen stores have cleared.
TruvoFit shows your 7-day average trend — so one spike never looks like the whole story.