A bit of a tangent, but the biking stuff is not relevant. What matters is your caloric consumption. Biking 25 miles, depending on your weight, is going to burn something like 1300 calories. For some contrast, a 2L bottle of coke has about 800 calories. So treat yourself to a big serving of Coke after (or during) the biking, maybe a fast food burger or whatever, and it's like you're not even biking at all in terms of caloric effect. This is also true with 'sports drinks' which are also loaded with calories which can be really easy to chug when doing cardio intensive work.

And this can easily happen because biking 25 miles is going to send your appetite skyrocketing. This is why working out to lose weight is probable one of the worst ideas imaginable. Working out is a critical part of staying in good health, but it simply has to be paired with a good diet, permanently. In other words you can't work away a bad diet at the gym (or on a bike), it just doesn't work.

Exercise is relevant, too. It's not just obesity and it's not just diet.

(And genes matter, too.)