Once the fatty acids travel to your liver, it starts producing ketones and, therefore, energy (ketosis). You may feel some difference, such as improved cognition and an increase in energy. The converse is true on a high-carb diet, where the bulk of your energy comes from glucose, and can cause a brain fog and make you feel sluggish.
Reference: Masood W, Uppaluri KR. Ketogenic Diet. [Updated 2019 Mar 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499830/