system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can I lose 2 kg or more of weight in a week, when each kilogram of fat has around 9000 kcal, and an average human male needs 16800 kcal per week?

So I've recently started a diet, plus going to the gym often, and I lost like 3 kg the first week (already consulted it just in case it was bad for my health, by the way), and I didn't lose muscle mass or water. How can I lose so much, when that's burning more fat per day than I'd need to if I didn't eat at all?
gpt
Firstly, you lose water. Also, with dieting comes the fact that you're literally storing less food in your body than normal. You'll probably bloat less with a diet change. Exercise contributes to calorie burning, too. Finally, your weight can fluctuate a little and scales aren't perfect.