In man's quest to feel indispensable (and indefatigable), maintaining a hyperambitious schedule—pulling all-nighters, squeezing in predawn workouts, turning happy hour into late-night cocktails—is the new normal. But men are suffering the consequences of limitless living more than ever: According to the Better Sleep Council, up to one in five men complains to his doctor of fatigue, and 42 percent say they'd rather catch z's than have sex. Worse, the risk of depression is seven times higher for guys who regularly feel worn-out. (Even the youthful aren't immune: Justin Bieber was hospitalized after reportedly collapsing at a London concert this year.) And since most of us can't call in sick with a bad case of exhaustion, it's time to become more stamina-savvy.

Could It Be Your Diet?
Why your seemingly healthy food choices may be replete with mojo-eroding missteps.

Mistake No. 1:
You start your day with a glass of juice.

Your morning O.J. is high-glycemic—it has almost no fiber, fat, or protein to delay sugar absorption, leaving you without fuel within the hour. "Reach for whole fruit instead," says Chris Melby, a professor of food science and human nutrition at Colorado State University.

Mistake No. 2:
You stick with low-fat foods.

Eating too few monounsaturated fatty acids can cause your testosterone levels—and therefore your ability to get up and go—to drop, according to Finnish researchers. A little fat from olive oil, salmon, avocado, almonds, dark chocolate, or oatmeal at each meal will help maintain energy levels all day.

Mistake No. 3:
You're a vegan.

Without vitamin B12—naturally found in animal products, including egg yolks, clams, and milk—you're susceptible to energy-zapping anemia. Melby recommends taking a B-complex vitamin daily.

Mistake No. 4:
You follow a Paleo diet.

Without carbs—yes, carbs—you'll be short on glucose (your main power source), warns Paul Arciero, Ph.D., director of the Human Nutrition and Metabolism Laboratory at Skidmore College. Because grains are out of the question, turn to low-glycemic whole fruits and vegetables. Greens, sweet potatoes, and berries work.