Overtime your metabolism goes up. Then you eat even more. Since energy can't be created or destroyed, you're technically just letting it pass through you βin and out. Since over time, the amount of energy going through your body increases, I'd argue that you gain more energy, both in and out through exercise.
I was taking poetic license with the notion that the equation for mass is almost entirely dependent on motion. [1] That's why I listed the equation first. Ah, well.
