It’s a good idea to observe the naturally slim people around you. I did and I found that while they ate a bit of everything they had instinctive hunger cues that made them stop eating a lot.
My sister is a natural size 4 and a junk food but she rarely has time to eat breakfast (she prioritises sleep and getting ready instead) and has her first proper meal at 1. That meal, when she’s in the office, is a hot meal and includes a small dessert and when at home is a bowl of cereal.
She drinks a lot of water. Eats a lot of snacks (she’s a crisp and biscuit addict) and doesn’t move very much. But if you total everything up barely eats 1600 calories. Eg she snacks instead of eating meals, she will skip dinner when she eats at work as she’s not hungry. When she eats dinner at home she cooks from scratch. She seasons her food a lot to add in flavour. She also eats out a lot but when she does that tends to be her only meal of the day. She also eats slowly and rarely finishes her plate.
By contrast I’m naturally a size 16, I don’t snack, eat minimal processed food, cook from scratch, and I eat small meals that balance carbs, fat and protein. I also move a lot. But I do admit I tend to overreat (usually 3k calories if I eat instinctively, but as I’m active I can lose weight eating 1800 cals which I’m doing now). I don’t like the taste of salty food, love spicy food.
BUT while my sister might be slim she has recently developed high blood pressure (the family curse) and is now overhauling her diet to be similar to mine because despite my weight my blood pressure is low.
So you can’t really win when you’re past 40 lol but make sure your fundamental diet is healthy. Dad’s cardiologist said thin people (women especially) tend to die of heart problems not just because of a lack of diagnosis - but also because society teaches us slim is healthy, so slim people often don’t take diet and exercise advice seriously. You need to focus on being healthy first.