Comment by JMTQp8lwXL

The body doesn't need carbohydrates to function. If you consume exclusively fats and protein (with very low levels of carbohydrates: less than 25g/day), the process of ketosis will kick in: your body will start converting fats to ketone bodies, specifically beta-hydroxy-butyrate, which as used as energy in the brain, heart, etc. instead of glucose.