I'm trying to keep my body from going from insulin resistance into full-blown Type 2 diabetes by watching my diet carefully and trying to exercise. My doctor recommended a low-carbohydrate diet, and the more I watch myself and try to maintain it, the more I see the connection between what I eat and how I feel. If I can stay on the low end of carb consumption, I'm much less prone to get headaches and I have more energy. If I overdo the carbs one day, I can pretty well guarantee I'll feel blah and bleah for the next day or two. I just have to be sure I am eating enough, frequently enough. Sometimes it's hard to find the proper balance.
It's VERY hard to be out and about and avoid sweets and refined starches, which seem to be my big bugabears. They are what I crave when I get cravings, even though they are a kind of poison to my body. Silly body — sometimes it gets confused and wants stuff even though it knows the stuff is VERY bad for it! So I try to tell it to decide what it really, really wants the most and how badly it wants it, and then I will maybe get a SMALL serving of it. I can tolerate small amounts of sugars and starches as long as I don't get carried away.
I'm still trying to work this whole eating thing out to see what is going to be do-able long-term. I wish there was a test that would tell you just what was right for you, without having to do all this empirical experimentation. When the experiments work things are fine; when they don't I pay, and payback sucks.