MRT2

You won't want to hear this, but my experience has been that I can keep the weight off, but only when keeping to a fairly strict diet, with regular vigourous exercise at least 4 times a week, at least an hour a day. As for cycling at a moderate pace, then I need to do even more, like maybe 6 or 8 hours a week.
The problem is, the body and metabolism are sneaky. I have lived this for over 30 years, getting fit, exercising, keeping the weight off, sometimes for 3 or 4 years at a stretch. Then life gets in the way, either because of work, school, injury, weather, and bad habits creep back in. Not all at once, but over the course of months or years. You only need to eat an extra 200 calories a day to gain 10 or 15 pounds a year. Or alternately, go from burning an extra 2500 to 3,000 calories a week with exercise to, say, 1,500 calories a week to have the same effect. Sort of like going from riding 6 or 8 hours a week in summer to riding a trainer 45 minutes 3 times a week in winter. You didn't drop down to nothing, but you did go from 2, 3 hour rides every weekend plus whatever exercise you did during the week down to maybe a few days a week on a trainer. Do that for 4 or 5 years in a row and you gain an extra 40 to 60 lbs.

You might say this is anecdotal, but I read something a few years ago where they studied people who had lost a lot of weight, and even years later, their metabolisms were still slower than they should be for their weight.

So if you want to keep the weight off, you need to be eternally vigilant.

Edit: my person opinion is, the body never forgets whatever highest weight it reached in the past, and that is your set point. Get lax in your diet or exercise and that is where you are headed. Throw caution to the wind, and you have the capacity to become morbidly obese. And it isn't a theoretical thing. Every day we all see people in our everyday lives who are pretty much there.