Pros and cons of cycling to work and back 5 days a week?

Balls. It's better than fuck all exercise (sitting on the tube) and if you push yourself it's a good 50mins-1hr of exercise everyday.

How can that not make a difference?

maybe he wasn't riding fast enough, and then stuffing his fat, greedy face with shitty junk food all day?

Nope. It's all the booze i drink, rather than the food i eat.