Naysayers have no evidence other than their feelings that "everybody's different", "that's not for me" and "I eat what I feel is best for me." When is the last time you weighed yourself naysayer. What is your BMI naysayer. What is your blood pressure naysayer. What does your bloodwork say about you naysayer. What pharmaceuticals are you taking for the rest of your life naysayer.
Recently a pescatarian I know (sometimes spelled "pescetarian" with an e) told me this very thing. She says eats what she feels is best for her what she is really trying to say is she loves to eat fish and won't give it up even if it shortens her life. Probably a smoker too. What's the difference. Both are habits that kill yourself slowly.
I explained to this pescatarian muscle is muscle, fat is fat, cholesterol is cholesterol and how the world's oceans have become toxic. I explained to her that throughout history tribes living by water with a high fish diet were riddled with heat disease. And I explained to her the myth of Eskimos leading long, healthy lives when they were in fact lousy with parasites and also succumbed to heart disease. Fish is calories though and humans are great at gathering calories. We are also great at doing what we want. We are funny that way. Selfishness is a synonym for the phrase "what's best for me".
Unfortunately for my pescatarian friend, feelings don't come into this. Feelings and evidence don't mix well. Neither do belief and knowledge. What one wants isn't necessarily what one needs. That's why parents (good parents anyway) don't let their modern entitled kids eat, watch, or do, whatever the heck they want.
Is everybody the same physiologically? No, of course not. But I'm talking about the vast majority of the human race. Not the minority with digestive issues, food allergies, or any other food related issues either born with or developed via poor lifestyle choices.
Regardless of how you perceive these "differences" among us (which are really not differences at all.. they are disorders or genetic abnormalities) the human metabolism, digestive system and nutrient requirements did not evolve to deal with high fat intake, sugar, salt, meat, dairy or eggs while leading a sedentary lifestyle. That is the recipe for vascular disease, high blood pressure, diabetes and cancer. Movement is life. Unprocessed actual foods are life. If we were had evolved to eat the SAD why do you suppose there is a healthcare crisis?
As adults we are nothing more than spoiled, old, children.