It would depend quite a lot on what meats he was eating and in particular if he was incorporating organ meats, but in general to breakdown protein and fat you need magnesium, potassium, and vitamins B and D.

There's also the fact that your pancreas can only create so much lipase and protease in a day. It doesn't matter what you do, there's going to be a maximum amount of fat and protein your body can absorb.

In Butter Boy's case he (a Florida Man) was literally excreting cholesterol through his skin.

I will give him this, though, people with beriberi can literally starve to death while eating the same amount of calories in carbs because they can't break down the carbs at all after a point. Meat and dairy has enough nutrients that you'll be functional until your heart explodes.

Or to put it another way, if you need 5 units of magnesium/D/B/whatever to process 2,000 calories of your butter and meat diet but you only get 2.5 from the diet you can "solve" the deficiency by eating 4k and excreting the other 2,000. Traditionally, or through your eyes, whatever works.

Compare that to needing 5 units of B1 to break down 2k of white rice but only getting .5 units from the rice or whatever (you'd have been fine in B1 from brown rice btw)

That's... Not really a good explanation but it explains the basic principle.