Food is fuel. The more energy one expends during an activity, the more fuel a person requires. In essence, sitting at a desk writing reports requires much less fuel [or food] than someone on the go running errands or breaking a sweat with an elevated heart rate for the same duration.
Over two years ago, Mardy Fish appeared maxed out. At 6-foot-2, 200 pounds, he suffered from chronic knee problems, joint pain and a stalled ranking. Was there a correlation between his weight, health problems and mediocre performances?