So, not to get all philosophical or anyzhing, but if you tf into a bigger form, like when I wolf out, you'd need to make more organic 'stuff' (unless you ended up being zhe same mass stretched over a taller frame) so you'd probably need to eat loads beforehand to provide all zhe energy needed to make all zhat.
Contrariwise, if you tfed into a smaller form, all zhat matter has got to go somewhere, so do you just....get really hot or somezhing as it all burns off?