Fibers, natural juice, skim milk, and some fruits/vegetables contain relatively low calories. If you eat a lot of them (as I do) , then I think they will add to body weight, and not only short term. I eat a lot of low-calorie foods so every day over 2Y my body weight is, say, 50% due to low-calorie foods, much higher than other people.

Therefore, if I eat lots of fiber (and other low-calorie foods), my weight could stay high in the medium term.

However, the weight-watcher’s focus should not be (limited to) measurable body weight, but rather the other part of the total weight.

When I eat lots of fiber, for example, i eat very little caloric foods like starch or protein. When this trend crosses a break-even level, the amount of energy I take in becomes less than my daily energy consumption so my body starts to use up “stored energy”, thereby reducing “the other part of weight“.

If gradually I also reduce my big amount of low-calorie foods (which presumably is very safe), the weight reading would slowly drop a lot. This would be superior to a temporary drop due to fasting.

https://www.healthline.com/nutrition/does-calorie-counting-work shows strong evidence that calorie is key to weight loss.

https://www.livestrong.com/article/507954-gaining-weight-when-drinking-water-and-eating-fiber/ is spot on about water and fiber causing temporary weight gain.