I hired a trainer at the gym last October and he is GREAT. He basically eats meat and not much else. That high protein / low carb diet really works for him — lean and strong.
I’d worry that is not a healthy diet, though. A good friend who was fit as a fiddle (lots of ice hockey, long hard bike rides, hiking in the mountains) suddenly couldn’t do a hike last summer. He had several stents put in the next day. His doctor said “plant based diet for you from now on” and he gave up all meat and his beloved crab and salmon. He loves going fishing and crabbing around Victoria, BC, Canada. I’m impressed he made the change, but that is brutal.
Keto is high fat, medium protein, too much protein is not good for you. The guideline I try to adhere to is your meat portion should be no larger than a deck of cards. I try to get my fats more from SMASH fish and nuts.
Many of the firefighters that I used to work with who were overweight refused to eat anything but meat. This usually resulted in temporary weight loss in the beginning and them smelling bad, feeling bad, and often collapsing at fire scenes when they had to exert themselves. The worst example was one of my drivers who eventually was transferred to fire communications after not being able to do his job in the field anymore.
He was supposed to come back to us after he lost weight. But he never lost any weight despite his apparent strict adherence to his meat only diet. Maybe he had a stash of twinkies and ding dongs hidden somewhere, but sweets other than a generous slathering of barbecue sauce never seemed to interest him. He eventually ended up having chest pains corrected with several stents. After that he was forcibly retired still in his 40s. The last time I saw him he was still morbidly obese and extolling the virtues of whatever carnivore type diet he was on.