What is optimum Nutrition?

Our physiology can be optimized through nutrition.  There is a biochemical level that is a threshold putting our body on an optimum plateau of health.  Everyone knows that junk food is bad for their body, and everyone knows that eating fruits and vegetables are healthy.  Plant-based diets have been found to be healthier then meat-based diets consistently in studies, so what plant-based diet is healthiest?  What do you think is the healthiest diet, the most optimal diet?