I know there are many causes and excuses for weight gain. But it's a fact that if you eat less calories than you expend, you will lose weight. I could name names, but I know several priests who are past middle age, even pushing old age, who are still in good shape. But these priests are very apostolic, and they frequently fast. They live a hard life of travel and mortification. But meanwhile, many other priests work to make their life perfect (easy life, nice priory, no overwork, good setup) and are rewarded on earth by gaining weight. That's what happens when your life is too easy. It's not just priests. Men strive to make their lives easy and convenient, and when they succeed, it only harms them physically. If your life doesn't cause you to delay or skip meals on a regular basis, you're pretty much going to gain weight eventually.