My guess is that while it may sound good in theory it would in fact be counterproductive, especially considering that we evolved as a tropical animal: need more water -> burn more fat –> generate more heat -> need to cool down -> sweat more -> need more water...
Of course, but metabolism also generates heat, and heat needs to be dealt with by evaporating water. Consider that the only human tissue that increases its metabolic rate just for the sake of it is brown adipose tissue[0], and its purpose is to generate body heat. On the other hand, compounds that can significantly increase base metabolism (and thus generate more water) such as 2,4-dinitrophenol[1] are dangerous because they can easily result in lethally high body temperature. That's why increasing metabolism with the sole purpose of generating water would be self-defeating.
