I go for months, when I'm losing weight, eating exactly the same foods in the same amounts every day, and with similar activity levels. I'll go for a week or more with practically no weight loss, or even gain a few pounds--and then down it goes again. Two days ago I weighed 161 pounds, yesterday 162, today 163. Water. In all probability, over that time, I lost body fat. No way to know that for sure, I've been eating 1900 calories of meat and fat, it's not impossible that my metabolism has slowed down enough that I'm not burning through body fat stores. But the increase in scale weight is no evidence of that. It's possible to be on a total water fast, and occasionally gain weight. I know that every time I've done what I'm doing now, over weeks and months, I've lost body fat.