I would expect Amdahl's law (or the general principle behind it; is there some brief name for that?) to apply to this particular case.

It's Amdahl's law-like only if you're lucky; if it's a simple nonlinear constraint system, then you get a bullet that's magic if and only if you are currently sub-optimal for glucose and there are no other crippling resource shortages.

In all other circumstances, the "magic bullet" will do exactly nothing.