Indeed, it's complicated, because urea is toxic, so long term living on protein is not that amazing for your health, plus slipping into ketoacidosis is a small

Indeed, it's complicated, because urea is toxic, so long term living on protein is not that amazing for your health, plus slipping into ketoacidosis is a small risk (high ketone and high blood sugar levels at the same time) if people are not strict about their diet (and we know strict dieting is hard anyway). But the basic idea is simple and works.