I agree you lose weight fast switching to an all animal protein diet. I did it once and lost weight quick. Didn't have the discipline to stick to it. Years later I researched the whole food plant based diet and discovered that the medical research was much more credible than the low carb diet.
Secrets of the Loma Linda Blue Zone diet: Centenarians’ good nutrition habits and whole foods as key
Wholegrains, vegetables, fruit and cancer risk - WCRF International
Since there is no society I know of that is exclusively animal protein, I hope the meat industry puts together a long term study for the carnivore diet. I can't find one. If the results come back positive then I will be persuaded and do a mea culpa.