Following the keto diet will affect your cortisol levels. This is because limiting your carb intake, to the degree that you do on keto, causes a starvation response in the body. In an effort to increase energy levels in the face of having less sugar, the body triggers the release of stress hormones like cortisol. The cortisol and other stress hormones will then increase insulin resistance and stimulate gluconeogenesis to help increase blood sugar levels. In other words, the ketogenic diet is stressful for the body at first.
When you are finally in ketosis consistently, however, your cortisol levels will decrease because you will be using alternative fuel sources like ketones and fat and have a greater capacity to spare glycogen (your body’s sugar stores). Thus, you will no longer need as much cortisol (and other stress hormones) to promote an increase in blood sugar levels.