Why did I gain weight overnight?
Water and food, not fat: a kilo of fat holds about 7,700 kcal, so a jump of one or two kilos in a day cannot be fat you have eaten.
A day of more carbohydrates, more salt or more food in general adds water, glycogen and gut contents. Glycogen alone is stored with three to four times its own weight in water, which is why the scale often jumps after a weekend and settles again by Wednesday.
To gain a kilo of fat you would need to eat about 7,700 kcal more than you burned, which is hard to do in a day.
Weigh yourself under the same conditions, in the morning after the toilet, and compare weekly averages instead of single mornings.
Run the numbers
Compare
Sources
3
- Kreitzman, S.N. et al. (1992). Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. Am J Clin Nutr 56(1 Suppl). Glycogen is stored with three to four parts water, so refilling it adds weight that is not fat.
- Orsama, A.L. et al. (2014). Weight rhythms: weight increases during weekends and decreases during weekdays. Obes Facts 7(1). 4,657 daily weigh-ins: weight rises over the weekend and falls again during the week, in people who were losing weight as well.
- Hall, K.D. et al. (2012). Energy balance and its components: implications for body weight regulation. Am J Clin Nutr 95(4). On how slowly body weight actually responds to a change in intake.