It is true to say that had someone gone for a brisk walk rather than, say, taking an afternoon nap, they would have utilized more energy for the duration of the walk. Sleeping itself, however, is not the cause of weight gain.

Is napping bad for losing weight?

Can napping help with weight loss? To date, there's no evidence to prove that napping has a direct effect on weight loss. Still, healthy sleep habits are important for overall weight management.

Does sleeping in increase weight?

Research suggests an association between sleep restriction and negative changes in metabolism. In adults, sleeping four hours a night, compared with 10 hours a night, appears to increase hunger and appetite — in particular for calorie-dense foods high in carbohydrates.