I found two contradicting views on what happens with water retention in a caloric deficit:
- Water goes down because in the caloric deficit we use up the glycogen which binds water
- Water goes up because in the caloric deficit the cortisol level increases
Both points can be made "even more true" with heavy exercising, i.e. we use more glycogen in muscles so less water stays in the body, we compound the cortisol increase so more water stays in the body.
Which is true? I suspect both are correct but everything depends on other factors/context which I don't know yet. If so, then what are these scenarios in which these claims can only make sense?
I saw people use 1) to explain why the weight loss can begin with a significant weight drop, i.e. the scale exaggerates the actual fat loss. This also explains the yo-yo effect when someone abruptly interrupts a fad diet and experiences a massive weight gain (it's mostly regained water).
On the other hand, I also saw articles that use 2) to explain why the weight loss may appear stale, without any weight drop or even with an increase, while there is a "hidden" ongoing fat loss. This also explains why a refeed can result in a weight drop, i.e. cortisol level decreases after caloric increase so water drops.