Fruit is high in natural sugars, like anything you put in your body over consumption of more than your body needs or can handle will be stored as a fat for later use. The body is good at converting the natural sugars in to glycogen for muscle fuel. The problem is people are not using as much muscle movement (desk jobs - i'm in the same boat during the day, but I make sure I exercise in the evenings)to use up the glycogen to replenish the muscle with the reserve fat stores.