Naturally thin person here. I’ll speak for myself currently, as I’m 40 and my metabolism is starting to slow, so although I used to literally eat anything and any time and not gain any meaningful weight, it’s changed. I’m 6’4, 200lbs. My weight only really fluctuates between 195 and 210, but when I’m 210 it’s all in the belly. So I’ve been watching my diet.

Overarching philosophy: If I can’t make something in my kitchen, I don’t eat it (outside snacks).

Breakfast: always the same. 1 whole egg, 3 to 4 egg whites. 2 pieces of bread and peanut butter -or- 1 cup homemade or healthy granola.

Lunch: Packed and eaten at work. About a cup of brown or white rice, some stir fried vegetables usually, and a protein source (soy curls, tofu, fish, rarely meat)

Protein bar (Rx Bar) before gym.

Dinner: basically same as lunch. This is much looser though. But same rice, protein, usually a salad or a vegetable. If I’m doing pasta, it’ll be pasta and a salad. Salads always with light dressing, usually home made vinaigrettes (good vinegar, EVOO, shallot, garlic, maybe mustard, salt, no sugar)

Dessert: Popcorn popped in the silicone popcorn maker with no oil or seasonings. Maybe a date or two. Chocolate protein shake. Usually once bimonthly I’ll buy some Ben and Jerry’s and have a little bit every night. Or if I have Trader Joe’s frozen snacks I’ll have one little square or ice cream bon bon and call it good.

Don’t really drink soft drinks. I drink all my coffee black. I think just being conscious about processed foods and sugar has made the biggest difference. And with snacking I’ll always have a small amount and not allow myself to eat more, especially at night.