For instance on that page about the Comanche it is claimed they only ate meat (which is absolutely inplausible from the start) but Wikipedia says they "also gathered wild fruits, seeds, nuts, berries, roots and tubers, including plums, grapes, juniper berries, persimmons, mulberries, acorns, pecans, wild onions, radishes, and tuna, the fruit of the prickly pear cactus. The Comanche also acquired maize, dried pumpkin, and tobacco through trade and raids."
Also, it seems, that meat is indeed not "nutritionally" complete and your source for that claim is some quack trying to sell his book?
It's great if a meat-only diet works for you, but I don't think there's scientific evidence to support it.