If you were eating the lean meat alone there would probably not be any sustainability issues but more than likely would not see the true benefits of going carnivore. I tried to morph the carnivore concept to another way of thinking and went with some leaner cuts and allowed the fat content to drop. (in my early stages of carnivore, I was only concerned with weight loss and only saw carnivore as a weight loss hack). I thought I could get into a calorie deficit by cutting the fats and still be eating carnivore. The weight loss stalled, and I actually gained some weight back. Once I adjusted the fat content back up, so the diet was higher fat/moderate protein, the weight began to fall again. The second thing I found, and this may just me personally, but when I am heavy on the lean proteins and don't 'add fat' the stools are still further between but going to the bathroom is a longer and can be somewhat constipated. The higher fat content for me helps keep me regular. If the venison is readily available, it is one of the better sources of meat protein. I would take advantage of that at every opportunity. One of the kicks/hacks I have been on lately since I switched to an all-red meat diet is that I melt butter and dip my meats, using the butter like a 'steak sauce'. In the case of venison, this would help bring the fat content up while eating lean protein. Babbling on. Good luck. Scott