Few people seem to realize just how much exercise is needed to lose weight - if that's what your goal is. Judging from how you describe it, you may be doing enough to help maintain or develop cardiovascular fitness in general, but that's not the same thing as losing weight.

It takes a lot of hours to burn signification calories. If you ride for half an hour, you can easily negate that just by drinking a couple of soft drinks, eating an extra cookie or two. It really takes a lot of exercise to beat the calories, and not much eating to undo it all. It's almost mandatory to absolutely eliminate all in-between meal snacks, and even at regular meals, to eat normal amounts without any extra, unneeded calories. And when I say "normal amounts", that's probably much smaller a serving than most people are used to nowadays.

There's a practical limit in the amount of time a person can spend exercising, due to other activities, work, etc., plus the need for some recovery time, time outs due to illness and that sort of thing. So for most, it will end up having to be combined with reduced calorie intake. The problem though, is that when you exercise, you need to eat. It can be tough to balance that with dieting. You do need protein for one thing, because if you don't eat enough of it, your body will consume what it needs from its own muscle mass. You would lose weight, but not from where you want to lose it. I know of no other way but to judge how you're doing by whether you are losing or gaining, and adjusting your exercising and dieting from there.

The bottom line is that exercises like cycling are great for cardiovascular and respiratory fitness, but on their own, they don't do that much for weight loss unless you spend a lot of hours doing them consistently almost every day. Even then, I'm sure many of us know a few long distance riders who wouldn't exactly be mistaken for Twiggy.