Why do we get fat? Because we’re overeating.
How do we know we’re overeating? Because we’re getting fatter.
And why are we getting fatter? Because we’re overeating.
Logicians know this kind of round-and-round logic as tautology. It’s saying the same thing in two different ways but offering no explanation for either. If we’re getting fatter, it means our body mass is increasing, our energy stores are increasing, and so we are indeed taking in more energy—calories—than we expend. Okay, we’re overeating. But by the same token, if we’re getting taller we’re taking in more calories than we expend. But nobody would say we get taller because we overeat.