Does protein turn into sugar?
Some amino acids can contribute carbon skeletons for gluconeogenesis, but that does not mean a normal protein meal simply turns into a meaningful amount of sugar. Gluconeogenesis is a normal, regulated process that helps maintain blood glucose when needed, especially during fasting, low-carbohydrate intake, and some high-protein contexts. In a controlled study using labeled egg protein in healthy humans after an overnight fast and a no-carbohydrate meal, dietary amino acids contributed only a small amount to glucose production over the following hours.
This matters for keto. True nutritional ketosis requires carbohydrate to be low enough, and in some people, very high protein intake can reduce ketone production because amino acids can support glucose production and because protein can stimulate insulin. That does not mean protein is "bad" or that it behaves like table sugar. It means that if your specific goal is sustained ketosis, protein has to be set deliberately rather than pushed infinitely high.
For body composition, the priorities are different. Protein and dietary fat are essential in a way carbohydrates are not: Your body needs dietary amino acids and essential fats, while it can manufacture glucose when needed. That is one reason carbs can be reduced very low if the diet is otherwise well-designed. It is also why higher-protein cutting diets can work well: Protein supports muscle retention, satiety, and food control, while some amino acids can be used to help meet glucose needs.
So yes, some "extra" protein calories can effectively be borrowed from a carb allotment if that improves adherence, hunger, and wellbeing. The tradeoff is that fewer carbs may mean less glycogen, flatter training, weaker pumps, or slightly less support for training output and partitioning through insulin and performance effects. But for many people in a fat-loss phase, higher protein and lower carbs is a useful tradeoff.
The practical answer is that protein is not free calories, but it also should not be feared as sugar. If you are trying to stay in ketosis, monitor protein in that specific context. If your goal is fat loss, muscle retention, or adherence, prioritize enough protein, then decide how much carbohydrate best supports training, satiety, and repeatability within your overall calorie balance.