I was a skinny mom, now a fat one, so I have seen both sides. As a skinny mom, I had a lot of rules about food, which I was happy with, as I liked being skinny. Generally, breakfast coffee and oatmeal. Lunch, small sandwich, salad, or tuna fish. Dinner, something small, with meat or cheese. No snacking after dinner or between meals. Candy gave me headaches, so very infrequent. No ice cream -- seemed needlessly rich and the serving too large. No nuts, cream cheese, cheesecake, fries. Don't like most dressings. Sugary cakes and cookies, ect also gave me headaches. No soft drinks -- water. Exercise program -- 4x a week. That is swimming 32 laps. I would say a high metobolism. A lot of coffee.
One day, after 32 years, I got tired of doing this. Inside of every skinny person there is a fat one trying to get out

I ate whatever I wanted. It took awhile to gain weight. Fries and chips. Starbucks. Steak. Baked potatoes. Beer. Wine. Cake with the kids. Pizza. Hambergers. Guacamole. Just use your imagination...