I took nutrition class in college when I was a sophomore. Freshman year, I started out pretty heavy, then gradually lost a lot of weight (going from about 220 to 170 or so). It was influenced by a few different factors: having sole choice in my food options for the first time in my life (my mom loved fatty indulgent home cooking), walking everywhere on and off campus, and not having a lot of money for food or a job to earn more money for food and/or booze. After living at home and working during the summer, I was about 180lbs and taking the class; we had a food diary requirement for a full week, but our intake was required to measure at least 1600 calories to count toward the assignment. It took me about two or three days to break the 1530 mark until I figured out that adding a couple pieces of fruit per day would do it. I still walked around every day, but having a steady source of income for groceries and not having any real intense exercise regime made it so that I was pudgy, but not fat throughout that time.
Eating small in combination with not enough activity is often where my problem lies; I often eat past satiety (clean plate club member), and sometimes eat to the point of feeling STUFFED. Given that I’m living in an area where everything is walkable or bikeable, I am able to maintain a lower weight; however, I am making inroads to correcting some of the bad eating behavior I learned as a kid and am taking more time to actually exercise, even if it’s walking uphill on a treadmill while reading a book/watching tv.