When I weighed 400 pounds, I didn't think or care much about what I ate or how it affected me. One of the ways I have learned to keep the fat off is to get sensitive to the foods I put into my body. I now pay close attention to how I feel after I eat.
Clams make me queasy so I don't have them. I used to eat dozens and then tolerate the stomachaches! A lot of foods give me bad gas, which I don't enjoy and neither do others! Meat always makes me feel "heavy," which I don't like. Orange juice and food don't mix well with me. Too much sugar gives me a boost, but lets me down later. Too much coffee makes me either jittery or tired.
Once I actually paid attention to the effect food was having on me, it was easy to make some changes: I now don't eat or drink things that make me feel bad!