2. Fat is the primary fuel source

When we eat fats and carbohydrates they are metabolised and stored. Carbs are broken down and stored as glucose in the muscles and liver, fats are circulated as triglycerides in the blood stream and stored as adipose tissue (i.e. body fat). Both of these are used for energy. Protein is broken down into amino acids and used to maintain and (if you're training) repair muscles and tissue, which includes your hair and nails. Long story short: you need to eat enough protein, but without adequate fats in your ketogenic diet, you will eventually run out of energy.