I've heard of fatty liver disease but haven't personally had any snakes directly affected by the disease (to my knowledge). When I kept similarly sized kings I fed them adult mice, jumbo mice, small rats, and chicks. I keep larger snakes now but I still feed a variety of prey types and sizes, including jumbo mice, jumbo rats, and occasionally even colossal rats for my largest snakes. I'll also give them medium and large rats, large hamsters, chicks, and rabbits. I tend to feed larger prey items with longer intervals between feedings. I've kept snakes for a few decades now and my experience has shown me that snakes are pretty hardy critters and fairly easy to care for. As long as you're not going overboard with the frequency of feedings or the prey size, and keep them in a proper environment, most snakes will thrive and live long lives.