You step on the scales one morning and you’re 1kg heavier than yesterday.
Brilliant. 😂
You trained. You ate well. You drank your water. You were “good” all day.
So how on earth have you gained a kilo?
The good news is, you almost certainly haven’t gained 1kg of body fat overnight.
Your body weight can fluctuate quite a lot from one day to the next, even when you’re doing everything right.
That number on the scales isn’t just measuring body fat. It includes water, food, muscle, glycogen and everything currently sitting in your digestive system.
So what might explain that sudden jump?
🍝 You ate more carbohydrates
Carbohydrates are stored in your muscles and liver as glycogen, and glycogen is stored alongside water.
So if you’ve had a higher-carb day, your weight might temporarily increase.
That doesn’t mean carbs have suddenly made you gain fat.
🧂 You had more salt
A salty meal, takeaway or meal out can cause your body to hold onto more water than usual.
Again – water, not fat.
🏋️ You trained hard
This one surprises people.
A tough training session causes temporary inflammation as your muscles recover and repair. Your body can retain additional fluid during this process.
So sometimes you can train really well and actually weigh more the following morning.
🍽️ You simply have more food in your system
If you ate a bigger meal, ate later than usual or simply consumed a larger volume of food, some of that food is quite literally still inside you.
The scales don’t know the difference between body fat and last night’s dinner.
🚽 You haven’t been to the toilet
Not glamorous, but very real. 😂
Changes in digestion and bowel movements can easily affect your scale weight.
😴 You’re stressed or haven’t slept well
Poor sleep and higher stress can influence fluid retention, digestion, hunger and your normal daily weight fluctuations.
🩸 Your menstrual cycle
For women especially, hormonal changes throughout the menstrual cycle can cause noticeable changes in water retention.
You might be doing exactly the same things with your nutrition and training and still see the scales suddenly jump.
And then, a few days later, they can drop straight back down again.
This is exactly why one weigh-in tells us very little.
If your weight goes:
Monday: 75.0kg
Tuesday: 75.4kg
Wednesday: 74.8kg
Thursday: 75.7kg
Friday: 74.9kg
…you haven’t been gaining and losing body fat every 24 hours.
That’s just normal fluctuation.
What we’re interested in is the trend over several weeks, alongside things like measurements, how your clothes fit, gym performance, energy levels and how you’re feeling.
So if you wake up tomorrow and the scales are suddenly 1kg higher…
Don’t slash your calories.
Don’t add an hour of cardio.
And definitely don’t decide that everything you’ve done this week has been pointless.
Carry on doing the basics properly and give your body enough time for the trend to tell you what’s actually happening.
Your weight can change overnight. Your body fat doesn’t work that quickly.
Erin Grant
Head of Gyms | MNU Certified Nutritionist
