This came from Dr Mirkin's newsletter. Interesting and it looks to me like its another reason that simply riding along does not do nearly as much as including some hard interval type riding into our rides.
Researchers at the University of Virginia show that
intense exercise is far more effective in reducing belly fat
than less intense exercise (Medicine & Science in Sports
& Exercise, November 2008).
Storing fat primarily in your belly usually means that
you have very high insulin levels which increase risk for heart
attacks, strokes, diabetes, metabolic syndrome and even some
cancers. Insulin causes fat to be deposited in your belly.
Exercise makes muscles more sensitive to insulin so
that you need less to do the same job. The more intensely you
exercise, the more sensitive muscles become to insulin. You
cannot exercise intensely every day because intense exercise
damages muscles and you have to allow time for muscles to
recover. However, you can check with your doctor to make sure
that you do not have a health problem that can make exercise
unsafe for you. If you pass, try to exercise intensely at
least once a week.