Why the scale went up overnight
You did everything right yesterday and the scale says you're up a kilo. It isn't fat. Here is what moves the scale from one morning to the next, roughly how much, and how to read your weight so a morning like this one stops mattering.
It can't be fat
A kilogram of body fat holds roughly 7,000 to 7,700 kcal of energy. A 1.5 kg jump overnight would need more than ten thousand extra calories eaten in a day. People don't do that by accident. What they do every day is drink, eat salt, eat carbohydrate, carry yesterday's dinner, and train, and each of those moves water.
What does move it, and by how much
| What happened | What it does | How long |
|---|---|---|
| A bigger day, or a late dinner | Food and drink still in your gut weigh what they weigh: a large meal and its drinks can be a kilo or more | A day or two |
| More carbohydrate than usual | Your muscles and liver store it as glycogen, with roughly three grams of water for every gram | A few days |
| A salty meal | Your body holds water to keep the salt diluted | A day or two |
| The weekend | In a study of daily weights, people were heaviest after the weekend and lightest by Friday; the ones who lost or kept weight off compensated through the week | Until about Wednesday |
| New or harder training | Working muscles hold extra water while they repair | Several days |
| Around a period | Many people hold some water; studies find about half a kilo on average, with big differences between people | A few days |
| A short night, stress, constipation | All move the scale a little and leave no trace in a food log | Varies |
Put two or three of these together, a salty Saturday dinner and Monday's first workout in a while, and a 1.5 kg jump is ordinary.
How to read your weight
Weigh yourself the same way most mornings: after the toilet, before food or drink. Then stop reading single mornings. Read the trend, a line drawn through the last few weeks of them. The trend barely moves for one heavy morning, and over a few weeks it shows what your body is actually doing.
A good trend also tells you how sure it is. Five weeks of mornings that scatter half a kilo either side of a slowly falling line can still say "down between 0.4 and 0.6 kg a week" with confidence. Two mornings can't say anything.
What Moderly does with a morning like this
When your reading jumps, Moderly looks at your own log for the reason: yesterday's food against your usual day, your own weekly rhythm, a first workout after a break, your period if you've turned that on. It says only what your data shows, and ends with what the trend did, which is usually almost nothing.
• Your Monday mornings usually read 0.4 kg above your trend: the weekend is still passing through.
Your trend moved up 0.1 kg, to 90.9 kg. One morning is noise; the trend is the number.
Start now, no account needed
Sources
- Orsama A-L et al. Weight rhythms: weight increases during weekends and decreases during weekdays. Obesity Facts, 2014.
- Fernández-Elías VE et al. Relationship between muscle water and glycogen recovery after prolonged exercise in the heat. European Journal of Applied Physiology, 2015 (about 3 g of water stored with each gram of glycogen).
- Hall KD. What is the required energy deficit per unit weight loss? International Journal of Obesity, 2008 (the 7,700 kcal per kg approximation and its limits).
- Medical News Today: weight changes around a period (a 2023 study of 42 people found about 0.5 kg).