Note the healthy skin and large, muscular, physique of the modern hunter-gatherer.
"It's basically nonsense combined with a lot of speculation & assumption of prehistory. For the vast majority of healthy individuals, there's nothing wrong with grains as long as you fit them into your macronutrient targets for the day. Aside from folks with clinically diagnosed celiac disease (CD), some folks claim to have a subclinical intolerance to gluten-containing grains (also called non-celiac gluten sensitivity; NCGS or simply GS). In my observations, most of those folks tend toward hypochondria. Nevertheless, there is emerging evidence in support of the idea that NCGS is a real rather than imagined phenomenon. So, the main challenge in this area is arriving at reliable diagnostic methods for GS. To quote a recent review-Until only a few years ago, almost the whole of the scientific world maintained that gluten would provoke negative effects only in CD and in cases linked to IgE-mediated allergies, both of which are rare in adults and more frequent in the pediatric population. More recently, however, progress has been made toward the hypothesis that a form of gluten intolerance exists that’s different from celiac disease, defined as non-celiac gluten intolerance or gluten sensitivity (GS), and it is estimated that for every person who has CD, there are at least six or seven people who have GS. Therefore, wheat allergy, CD, and GS combined together may affect about 10% of the general population."