I have seen studies that say both. Bodybuilders do it to lower cortisol, burn fat and build muscle, but that is following strict rules of the Keto diet. I have seen a couple of other studies of low carb diets that say it raises cortisol. I don't know if the results differ if your body is in keotosis (Keto Diet) or if your just lowering carb intake. Maybe people just respond differently based on their health.