The less you mess with nature, the better.
Yup, that's my basic theory of nutrition. The whole thing. Toldja it was basic! ☺ While almost painfully simple in theory, it's just that in practice it's sometimes a little harder.
Not messing with nature means cooking from scratch, not from prepared anything. That takes time.
Not messing with nature means supporting sustainable horticulture and agriculture--which means using organic vegetables, and pasture-fed animals. That takes money (or time, if you grow them yourself).
Not messing with nature means using real foods instead of synthetics, like butter rather than margarine, even though it costs four times as much.
Not messing with nature means eating in season, even if you're craving tomatoes in February.
Not messing with nature means eating things that grow where you are, rather than picking them green and shipping them 3000 miles (or 10,000!) just so you can have everything all the time everywhere. Ideally it means participating in the law of the harvest by growing and harvesting at least some of your own food (both plant and meat sources).
It means eating the best things, not just the cheapest or easiest things.
Do I do all these things? Not perfectly, no. Not yet anyway. But I believe in them, and I strive for them.
Assorted posts on the subject
What Constitutes "Good" Food (in my book anyway!)
The Problem with Synthetic Vitamins
Why I'm NOT Vegetarian
(links added as they are written)
Animal, Vegetable, Miracle by Barbara Kingsolver
In Defense of Food by Michael Pollen
Fast Food Nation
The Omnivore's Dilemma by Michael Pollen
The World According to Monsanto
The Future of Food
Other Good Links
SlowFood (a counteraction to Fast Food and Fast Life)
AnimalVegetableMiracle (Barbara Kingsolver's site about her "year of food life")