When you’re trying to lose weight, it’s easy to obsess over the numbers on the bathroom scales as you measure your progress. But fear not, daily weight fluctuations are nothing to worry about and I guarantee you have not put on more fat overnight.
Small daily variations in scale weight are completely normal. For example, your weight might increase after a meal, a delay in bowel movement, or during the premenstrual phase in women, and may decrease after exercise from fluid loss associated with sweating or going to the toilet.
If you need more convincing, then consider that one pound (~½ kilo) of body fat contains about 3,500 calories (~14,700 kJ) of stored energy. So in order for you to gain three pounds (1.36 kilos) overnight, you would have to consume an additional 10,500 calories (~44,000 kJ) over and above your usual calorie intake!
Try not to fixate on your daily weight, but if it helps you stay on track, weigh yourself once a week at the same time of day under the same conditions (for example, before exercise and meals) for a more accurate reading.