Is exercise work or play? Weight gain or loss depends on your answer

It’s a common rookie mistake, but plenty of diet-and-exercise veterans make it, too: With an act of will, you muster yourself to the gym or the track, and you gut your way through an arduous workout. When you sit down to dinner or go to the break room later that day, you say to yourself, “By God, I’ve earned this (sugary soda, yummy snack, second helping, dessert, second glass of wine). I worked hard today!”

A week or so later, you’re standing on the scale wondering what happened.