Momentum article summarizes long-term medical study on benefits of cycling for women. Meaning 1/2 hr. of regular cycling.

http://momentumplanet.com/articles/b...off/index.html

http://archinte.ama-assn.org/cgi/con...urcetype=HWCIT

Well, some cycling is better than no cardiovascular activity/exercise.
If I was riding flat terrain for half hr. daily, not sure if I could control my weight. I would require more cycling time on daily basis..or 1-2 steeper hills on the regular route.