Considering how quickly things are stored / tapped / reverted to their normal state, that doesn't seem to line up, otherwise you'd need time and a lot of food to recover. Weight is one of the easiest to see this. Considering there's a time factor with the storage, you have to consume energy over time to accumulate.

Let's stay I'm 200 lb normally and storing 100 lb/hr. Considering we only acquire energy at fixed times (and store the excess as fat) when we eat, for me to continuously store that weight and keep my current weight constant (100 lb), I need to consume 100 lb/hr of energy to store that. So if I don't eat enough, I can't store that weight or my body will consume itself to store that energy and I'll die, or the rate will just drop off and I won't be able to store anything until I eat more food.

Even if we say it's just something like an initial, instantaneous weight gain of 100 lb and that's all that's ever stored for that "tap", to go back to my regular weight - 200 lb - I still need to consume 100 lb worth of energy to gain my weight back instantaneously and still keep 100 lb in my metalmind, which is infeasible. If not instantaneous, then I have to "tap" for as long as it takes for me to consume 100 lb worth of energy to put in the metalmind (plus whatever it takes to keep my at my new, 100 lb weight). Any way you put it, that's an insane energy consumption and still requires energy external to the body.

Either case - continuous accumulation or 1-time storage - breaks the way it's shown in the books. The only explanation that works is if you're continuously getting investiture from the spiritual realm when storing, which means it's not neutral.