They said nothing about drinking. It is pretty common parlance to use "fast" to mean "without food/calories" (i.e. water is completely kosher, and some argue "black" tea/coffee/diet soda is too as it is 0 calories/negative calories).
One warning - tea isn't necessarily kosher, because some artificial flavors are made from non-kosher ingredients.
I don't think he's referring to kosher as confirming to kashrut. I think he's using it more literally as hebrew for "fit".
Most medical fasts recommend avoiding artificial sweeteners during extended fasts as they cause the release of insulin through the incretin effect.
I can’t speak for OP, but most fasts of this kinds allow drinking water at the very least, and sometimes even light broths like chicken broth. Religious fasts, on the other hand, often don’t even allow drinking water.
However it turns out some religious fasts allow you to eat whatever you want after dark, or something like that. The discovery of which tempered my awe somewhat.
Yeah, a lot of Muslims gain weight during Ramadan.[1] And I think they'd point out that the intent is spiritual.
Although as others pointed out, Ramadan in Islam does not.
The terms set tasting and dry fasting are sometimes used to distinguish between fasting from food and fasting from eating and drinking. For weight loss fasting, it's usually wet fasting if not specified.
The fasting discussion in this thread seems to be about caloric fasting, rather than religious fasting. The latter tending to prohibit drinking, while the former doesn’t.