Healthy Lifestyle Keto The ketones then become the primary source of fuel for the body. Ketones provide energy for the heart, kidneys and other muscles. The body also uses ketones as an alternative energy source for the brain. I started a Keto diet today, but I am struggling as a pescatarian to make it up to the daily fat intake/basically to eat enough so that I'm not hungry. I think that this has been the issue with my weight gain over the past few years -- I've been eating a lot of carbs for t...