I stopped training for centuries because I was gaining weight. The really long rides made me very hungry for days, and also too tired to do any exercise for days. So now I generally limit my long rides to 40-50 mile rides, with a few 60ish-mile rides each summer. This way I'm able to remain consistently active instead of seesawing between huge bursts of activity and couch potatodom.
BTW, I highly recommend Nancy Clark's Sports Nutrition Guidebook. I really like her approach to eating for weight loss.
http://www.nancyclarkrd.com/books/sportsnutrition.asp