There is no particular reason you should listen to me except maybe that I have read and synthesized a wide variety of expert opinions. I think you would be surprised by how much experts disagree -- I would say the level of disagreement among nutritionists exceeds that of economists. So if everyone has a different opinion I figure adding mine won't hurt.
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First and most importantly, there is no optimal diet. There are a wide variety of healthy diets. However, the typical American diet is not one.
As a general rule, it is a good idea to eat foods like our ancient ancestors did, meaning foods that are naturally occurring and can be easily digested without being cooked. One thing to consider is that most (all?) of the foods that we can find in the grocery store and think of as naturally occurring look and behave nothing like what our ancestors would have eaten. Corn, bananas, grapes -- seriously I cannot think of an exception -- are bigger and juicier than they were because they have been selectively bred over many generations. Some are not only bigger and juicier but fundamentally different from the plants our ancestors would have known. So the advice "eat like your ancestors" is not as straight-forward as it first appears.
Would you recognize these as corn and bananas?
Animal products should probably be a small part of the diet -- certainly not every meal, maybe not even once a day -- but there are cultures with good health and low rates of heart disease that subsist on basically meat alone, and I have a hard time explaining that.
Seth Roberts has convinced me of the value of fermented foods, so I have been trying to add those to my diet, mostly in the form of homemade yogurt. I am not sure how much it matters; I have not noticed any significant difference in the way I feel. (Switching from a typical American diet to a mostly vegan diet, though, I definitely felt a change for the better.)
On pesticides and preservatives and hormones and things, I am not really sure. Of course they are not good for your health but I have not been convinced that they are extremely bad either. There is probably some truth to the alarmists' claims, but the fears are probably overblown.
In the end, because I do not believe in an optimal diet, I am not sure diet matters much as long as you avoid eating crappy foods. I think bad foods probably kill you faster and lower your quality of life more than any mix of good foods make you live longer and raise your quality of life. So instead of going super-food crazy (acai berries, I'm talking to you) or stressing over the variety of foods in my diet, I live by the principle avoid crappy foods.
