That's a fair question and I'll give you a fair answer. At present, there is no scientific evidence that a 100% plant-based diet is the best diet (I know that 'best diet' is incredibly loaded, but let's take it as being the diet that is associated with the best health outcomes, i.e. longevity, low risk of chronic illnesses, etc.). However, what we have is 1) short to medium term studies on the health benefits of a plant-based diet supporting that position and 2) (among others) supportive science in the form of the 'Blue Zone' studies. I've touched a lot on the fact that vegans have lower cancer, diabetes, CVD, etc. risk, so I'd rather discuss the 'Blue Zones'. Basically, these are communities around the world which have the largest proportion of centenarians and lower occurrences of typical chronic illnesses and diseases. Now, when you look at there diets, they eat a 90-95% plant-based diet, with little to no processed foods. There are also other important lifestyle elements: strong sense of community, regular low intensity exercise, low stress and so on. So, it would be fair to say that at present and based on current evidence, a 90-95% whole foods plant-based diet is the 'best diet'. However, there are a few things to take into account: 1) many studies have shown the dose-response relationships of plant foods, whereby eating more, accords a greater benefit 2) in the near future, we'll be have the benefit of long-term studies who have looked into vegan diets over the long term 3) that final 10-5% I choose to stick my ethical convictions in - I don't want to hurt or exploit animals, so I'm not going to eat or wear them and neither do I want our planet to be destroyed for that purpose. I think that we're not that far away from a point where there will be prevailing scientific consensus that a whole food plant based diet will be associated with the best health outcomes in the majority of a population.
