Originally Posted by
50PlusCycling
It makes a bigger difference than you realize. The amount of effort needed to carry around extra weight is considerable, and when that weight is removed, the energy savings goes a long way to improving your speed and endurance. I used to live in a place where I could ride all year, and my weight stayed consistent. Then I moved to a country which has 4 seasons, and winter riding is impractical. During the winter months I invariably put on weight, and as I get older, the weight packs more quickly. When I start riding I can feel the extra effort needed to move that weight around. As the weight comes off, everything becomes easier, and when I get back to my optimum weight, I find things like stairs, hikes, and long dog walks much more pleasant.
I have, though, gone too far the other way, working out a lot while not eating enough to maintain muscle mass. I did that before I went back to cycling so I don't know what effects it would have on my speed, but I generally found myself looking muscular because of the lack of fat, but actually lacking strength to push open heavy doors easily, etc.