Anecdotally, my improvements have come with eggs and cheese daily for brekky, fish oil pills when I'm not eating fish twice a week, mostly cow and lamb with occasional chicken or pork. Before carnivore I loved chicken and shunned most other meats but my tastes have changed to prefer reds. I'm also better and understanding what my body seems to need (not sure if that's the exercise or dietary changes) so I assume there's some better nutritional value in reds.