To test this theory, researchers took people on a hike. Half the participants were told they were going on the hike for exercise, and the other half were told they were going on a scenic walk for fun. The hike itself, though, was exactly the same for both groups.
After these hikes, participants were provided with a meal or a snack, and they were allowed to eat as much or as little as they wanted.
The results were fascinating.
People who thought they were hiking for exercise ate 35% more chocolate pudding after their workout than those who thought they were taking the scenic walk. In the other protocol, the hike-for-exercise group ate 206 more calories in M&M's than the hike-for-fun group.
Basically, those who went into exercise assuming it would be an enjoyable experience rather than "work" ended up eating considerably less after their workout.