The turning point for me was when I started feeling how different my mind, stomach, pooper, and muscles each felt after eating certain foods. I've switched from a meat-heavy high-protein diet to a vegetable-heavy, fiber-focused high-protein diet, and I can tell the difference by lack of sluggishness and an improved recovery time, among other things.
What I'm saying is that you need to look at things structurally. What you eat, what's in what you eat, how much of it you eat, and when you eat it. What you do (physical activity), how much you do, when you do it. How you feel throughout the day. Any health concerns you may have (diabetes, insomnia, anemia, etc).