Fung defines fasting as not eating, something you choose to do and can break at any time, whereas starvation is imposed on you and you never know where your next meal is coming from. For that reason starvation also imposes stress, cortisol increase etc. that are bad for health.

But one thing I've found in researching scientific articles on "fasting" and "starvation" is that everyone defines them differently (or more commonly not at all, you have to infer their definition). Several "fasting" and "starvation" articles shocked me when half way through the paper they start taking about what their subjects were eating even though the abstract never mentioned food or drinks; I had assumed water only, but then had to start back on page one re-reading with the new-found definition in mind. In Keys' "starvation" studies, subjects were eating 1500 cals/day (really calorie restriction studies since they were underfed by 500-1000 calories/day). Chief Theresa Spence was on a "hunger strike" that involved drinking fatty soup all day, probably more calories than she normally consumed.