I ride a lot. I've logged over 14,000 miles since August 03. All of these miles except for 1800 have been on mountain bikes with fat knobby tires and mainly on rough unpaved roads. (the reason i mention this is because these are HARD miles. much harder than rode bike.) I have burned tons and tons and tons of calories.
I have eaten, tons and tons and tons of calories. Riding a lot requires one to eat alot. This morning I rode 34 miles in 20 -30 mph winds on gravel and dirt roads, with quite a few hills. I apparently burned a lot of calories because i have been eating like a horse all day and I am still hungry. I ride every day but todays ride was hard because of the wind and I tagged on some extra miles. Also had some mud to contend with.
I am 6'2" and 145 lbs, down from a pre-biking 200 plus. Here are the things I can remember that I ate today. 2 energy bars, 4 large cinnamon rolls, 2 large chicken breasts, 2 slices garlic bread, 3 helpings of grilled potatoes, pasta salad, a half box of wheat thin crackers, lots of hard candy, bowl of icecream, 3 bowls of cereal, 3 rice crispie treats, baked beans, two ears of corn, 5 large chicken fajita quesidillas, 3 diet cokes and two light beers.
And I am still hungry!
There is a point to this story. My metabolism is high. My body, knows that it needs to eat because at sun up tomorrow I will be on the bike again and churning hard. It knows this because i have done it virtually every day for 2 years, through freezing winters and hot summers.
It will take time for you to achieve weight loss through biking. The distances you mention are not going to burn much fat if you don't strictly monitor your diet. Look at everything I ate today. About everything is low in fat. That is the way I have eaten for a couple years as well. Doing something similar for yourself without any exercise will likely lose you 1 lb per week.
Ratchet up the riding and you likely can increase that. Just don't get on the bike and ride 10 miles and expect to lose weight, at least not much. The table is a much better place to do this. However, if you start riding 200 or so miles per week than you have a different story.