Look, I don't want to waste your time. As I'm sure you have done, I too have spent a great deal of time pondering questions of health, diet, and exercise. Here's what I know for sure:

-All organisms are products of evolution, which means they adapt to their environments over time. "Environment" means all surrounding conditions: temperature, water, sunlight, air, food, etc.
-Humans are no exception. Given enough time and a stable environment, we become well adapted to that environment.

If you agree with these two assumptions, then I'm fairly comfortable in concluding this: the optimal diet for humans is the one to which we are best adapted.

One more thing: evolution is slow. Civilization has only been around for about 10,000 years, a blink of the eye on the evolutionary scale. And you could even argue that our dietary fitness isn't even being selected for much anymore (since making it to sexual maturity and having as many offspring as you'd like is a pretty easy thing to do these days).
So then, if you want to know what you shouldn't be putting in your body, simply work backwards.
-Artificial foods.
-Refined sugars.
-Grains.
-Dairy.

Beyond that, things get more difficult. What did we spend millions of years doing? Maybe we ate no meat. Maybe we ate nothing but fruit. Maybe we ate nothing at all! But I doubt it. My best guess is that we were hunter-gatherers (who possessed fire for quite a while) and this is what we ate:
-Meat
-Vegetables
-Fruits
-Nuts

But look at the evidence and figure out what you think we are adapted to eat. If you do that and we get a different answer, I really won't hold it against you. If, however, you want to keep eating things that were just invented yesterday.... well, I'm sure you're already adept at rationalizing illogical decisions.