When I was in my 20s, 30s, and early 40s I had to eat 2,500-3,500 calories a day to maintain a weight of 107. I had a very fast metabolism and I was athletic and burned a lot of calories. I would go on a cruise and come back 1-2 pounds lighter while my friends would gain 5 pounds. I was always thin and muscular until I got in a very bad car accident in 2000 and went on meds. Now I eat about 1,800 calories a day to maintain 125 pounds. Most of what I eat now is lean protein (organic turkey/chicken & wild salmon, Greek Yogurt) lots of fruit, oats, nuts and veggies. When I go above 2,000 calories a day, I slowly gain.