Sure, it's simple. A newborn baby doubles it's weight in a month. Why? Because it's eating a lot. A woman gets pregnant and puts on 30 pounds? Why? Because she'

Sure, it's simple. A newborn baby doubles it's weight in a month. Why? Because it's eating a lot. A woman gets pregnant and puts on 30 pounds? Why? Because she's eating a lot. A teenager goes through a growth spurt and puts on 20 pounds? Why? He's eating a lot. A cancer patient loses 20 pounds quickly. Why? He's not eating much. But this might not be the most useful level of abstraction to look at. It's sort of like looking at this comment and thinking that it's on your screen because your computer fetched it from your wireless router.. true, but not very useful or informative. You might want to step back and ask why these people are eating so much or so little. Surely it isn't just willpower (whatever that is). There are plenty of slender people who can't bring themselves to do things like study for an exam.