Apologies in advance for the pedantic response, but the human body can generally make enough glucose from protein to keep you out of ketosis. You usually have to restrict both protein and fat to reliably induce ketosis. You can confirm this for yourself with ketone test strips. Most dieters on so called ketogenic diets are not actually in ketosis.

Even more surprising is that fermentable fibers get converted into short chain fats by bacteria in the gut that are ultimately metabolized as ketones, so a diet high in those can induce ketosis even with a high carb diet. Some herbivore animals are always in ketosis, and some carnivores are almost never in ketosis unless they are starving and can’t find protein.