Being skinny doesn't mean you are healthy.
Truth. My brother is pretty much the width of my small finger. It isn't healthy.
I see a lot of people going "oh well sports and exercise really aren't my thing." That's a load of bull, regardless of genetics and environmental factors growing up every human is capable of doing some athletic activity, even something as simple as a jog around a regular middle class house.
Too many people don't realize that you actually
need carbohydrates and calories in order to actually keep living, except
overconsumption of these two factors added with lack of exercise is why you start sucking wind right with something as simple as running up stairs.
I've been doing biology on this recently and know exactly how not to be fat: It's all about the HDLs and LDLs (High-density and low-density lipoprotein) Basicly LDLs make you fat and unhealthy (Prone to heart diease etc.) HDLs make you fit and healthy. (Olive oil, natural oils, Lentils, Fish, Walnuts) There is more to it than that but I can't remember exactly. Combine HDLs with a fair bit of exercise/sleep and you'll be very healthy and slimmer.
That's called cholesterol. Sure, they help a bit but you still need to balance everything else.
And on that point, I'm going to say this: There is no "ultimate easy plan". There is no "secret" to it. You eat a balanced diet for a normal human being, you exercise a normal amount at least once a day, and your body is pretty much in "normal" fitness. Your diet and exercise depend on your weight, height, etc.
Oh and if you're 14-15 years old and you're starting to eat a lot of food, don't freak out. You're not getting fat. If you eat a lot and sit on your ass a lot then you will, though.