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.
Professional tennis players expend tons of energy during match play, especially if you’re Andy Murray, who competes long and hard and generally advances deep into tournaments.
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?