I think this is actually fair when vs. a claim, but not so much when taking a position. When the truth of things is up in the air, both sides can do this--and should listen to each other. Sometimes the null hypothesis should be no hypothesis. We can establish that there are situations where saturated fat does no harm--basically because there are unharmed populations (when it comes to diseases of civilization). Also that there are situations where polyunsaturated fat does no harm--the unharmed !Kung, at least until recently, based their diet on the mongongo nut, around 60 percent is the number I saw, and it's a nut that's typically high in omega 6. That can never show that these fats are always safe, paddling around in a half inch of water doesn't show the impossibility of drowning. On the other hand, we have epidemiology that shows that it's possible to eat these fats and get sick. I think the article that started this had a quote along the lines of "we don't know why traditional peoples can eat coconut and be fine, so prudence is to avoid coconut," okay, that's why I very much disagree with the brand of Paleo that shakes its head at "reenactment." It's possible to know the probable effect of a set of behaviours without knowing the exact mechanisms--this seems like probably a sort of learning with a long history, animals learn a string of behaviours, and then perhaps through error they'll skip a step, be surprised when they still get the desired effect, and stop doing the unnecessary step. Maybe a kick in the ego to revert to a sort of pre-sentient learning, but it's worked for billions of years, we'll probably need some of it for a bit longer.