Human pre-history was also mainly carbohydrates. The idea that humans lived off of primarily meat is fantasy - we eat more meat now than we ever have. Prehistorically, humans ate primarily gathered foods - nuts, fruits, and vegetation. I believe it's something like the average prehistoric human ate 100 grams of fiber a day. As opposed to the US ~ 2 grams of fiber a day, caused by our diets high in meats, saturated fats, and ultra-processed foods.