The answer is this - unless you are doing at least 500 miles per month, no. From doing a quick survey of other middle aged cyclists that I know, that seems to be the magic number. At 600 miles a month, you start to pull in the belt notches every few weeks. At 700 miles a month, you can almost see their body collapsing in upon itself.
Which makes me wonder about the regular government advice about doing 30 minutes of activity per day, or whatever it is.
Doing 500 miles per month at a reasonably steady clip will require you to be on the bike for 30-36 hours. At least 1 hour per day. Every day of the month. 600 miles requires 1.5 hours every day of the month - and we're talking about sweaty miles too. 700 miles is 1 3/4 hours per day. Not per weekday - per day. If you miss a day, you need to do 3-3.5 hours the next day to make it up.
I'm using an average speed of 22km/h, which is what you tend to get in parts of Sydney after accounting for Stop signs, traffic lights, pedestrian traffic on shared paths, traffic congestion and hills. The more time you spend waiting at red lights or stuck behind someone walking a dog, the lower your average speed. In order to average 22km/h, I need to be doing 30km/h or faster on the flat, open bits of road.
That's a hefty time commitment to exercise, which is probably why most of us are getting fatter. The only way I manage to do between 400 and 600 miles per month (1-1.5 hours every day) is to do the following:
1. Ride to and from work - it's time I would have spent walking to a bus stop, waiting for a bus and sitting on a bus, so riding is a good alternative use of that time
2. Give up TV. Surprisingly, that was not hard. The main problem with watching TV is that I was staying up late, which meant I was getting up late, which means I couldn't get that extra 15-30 minutes on the bike in the morning that you need to get your average riding time up. Speaking of which - time to go. The sun will be up soon.