believe it or not, by your definition carbs are also essential, it’s just that the body can produce them

Protein -> carbs by gluconeogenesis

Isoleucine and phenylalanine are exclusively ketogenic and produce ketone bodies.

Leucine can be used to synthesize fatty acids in adipose tissue.

The only 2 fats that we really need are omega-3 and omega-6, but not in huge amounts, thankfully, both not from meat.

Point is, one can more readily survive without a major source of fat or carbs.

* it‘s hypothetical

* the ill effect is diarrhea

* some people have lived off a meat only diet successfully

* personal theory is the problem is not excess protein, but lack of fiber and gut biome degradation

Any mono-diet is nutritionally a bad idea, especially taken to extremes. But — one would simply not survive at all on a monodiet of pure fat or carbs.