Why Your Weight Jumps 2 Pounds Overnight: Water, Glycogen, and Sodium Explained
October 21, 2026
It is common to eat well, train hard, and see the scale rise by 1 to 2 kilograms the next morning. Body fat cannot change that fast: gaining a kilogram of fat requires a surplus of roughly 7,700 calories. The jumps reflect changes in water, glycogen, digestive contents, and sometimes hormones. Understanding where these swings come from helps you avoid overreacting and see the real trend.
A typical adult's body weight varies by 0.5 to 2 kg over a day or two without any change in fat or muscle.
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Glycogen is the stored form of carbohydrate in muscles and the liver. Adults store roughly 400 to 500 grams of it, and each gram is bound to about 3 grams of water. That means 500 grams of glycogen carries about 1.5 kg of water, for a total of about 2 kg of weight. When you cut carbohydrates sharply, glycogen is depleted and the associated water is lost, so the scale falls by 1 to 3 kg in the first week of a low-carb diet. When you resume carbs, the weight returns.
This explains why low-carb diets show rapid initial losses, and why a high-carb meal or a refeed day can cause a temporary increase of 0.5 to 1.5 kg.
Sodium, Food Volume, and Hormones
A salty meal makes the body retain extra water to maintain sodium concentration; a restaurant dinner with 3,000 to 4,000 mg of sodium can cause a 0.5 to 1 kg temporary rise. Food and fluid in the digestive tract have weight: a large meal of 1.5 kg of food and drink raises weight until it passes. Bowel movements, hydration, alcohol, and exercise (muscle inflammation and fluid) also influence daily readings.
For women, the menstrual cycle can cause water retention of 1 to 3 kg in the days before and during a period, due to hormonal changes. The weight often drops suddenly afterward.
| Cause | Typical effect on scale | How fast it reverses |
|---|---|---|
| High-carb meal after low-carb days | +0.5 to 2 kg | Days |
| Very salty meal | +0.5 to 1 kg | 1 to 3 days |
| Large meal still in the gut | +0.5 to 1.5 kg | Hours to a day |
| Menstrual cycle | +1 to 3 kg | A week or so |
| Hard workout (inflammation) | +0.5 to 1 kg | 2 to 4 days |
| Dehydration | -0.5 to -2 kg | Rehydrate in hours |
How to Read the Scale
Weigh at the same time each day, ideally first thing in the morning after using the toilet and before eating or drinking. Record every reading, then calculate a 7-day average. Compare this week's average to last week's. A decline of 0.2 to 0.7 kg a week in the average indicates real fat loss for most people. Do not draw conclusions from one day.
If you gain 1.5 kg overnight after a restaurant meal, that is almost certainly water and food volume. Expect it to subside in several days if you return to normal eating.
What Real Fat Gain Looks Like
To gain 1 kg of fat, you must eat roughly 7,700 calories more than you burn. A single huge meal of 3,000 calories above maintenance adds at most 0.4 kg of fat. So a weight spike greater than that is not fat. Persistent weight increases over several weeks, supported by a larger waist measurement and tighter clothes, signal a real change in body composition.
Using Other Measures
Take waist measurements, progress photos, and track strength. If your weekly average is stable but your waist is shrinking and lifts are rising, you may be losing fat while gaining muscle. Do not let the scale be your only guide. If daily weighing makes you anxious, weigh two or three times a week or use a different measure.
Frequently Asked Questions
Why did I gain 2 pounds overnight?
Almost certainly water, glycogen, salt, or food in your digestive system, not fat.
How much water does glycogen hold?
About 3 grams of water per gram of glycogen.
Why do low-carb diets cause fast initial weight loss?
Glycogen depletion releases a lot of water, often 1 to 3 kg in the first week.
How often should I weigh myself?
Daily with a weekly average works well, or two to three times a week if daily is stressful.
How long does water retention last?
From hours to a week, depending on the cause.