President Obama with McChrystal in the Oval Office in 2009. Pete Souza via Wikimedia Commons Even while he was working long hours at the Joint Special Operations Command and then later overseeing all NATO forces in Afghanistan, Gen. Stanley McChrystal was eating just one meal a day.

The 60-year-old retired general continues to maintain the strict diet as a civilian, but why? He likes the "reward" of food at the end of the day, as he said on the "Tim Ferriss Show" podcast.

"When I was a lieutenant in Special Forces many many years ago, I thought I was getting fat," said McChrystal, who cofounded The McChrystal Group and recently penned the book "Team of Teams." "And I started running, and I started running distance, which I enjoyed. But I also found that my personality is such that I'm not real good at eating three or four small disciplined meals. I'm better to defer gratification and then eat one meal."

For McChrystal, the one meal he eats is dinner after he is finished with work, which he said was usually around 8 to 8:30 p.m.

"I sort of push myself hard all day, try to get everything done, and [then] sort of reward myself with dinner at night."