The ketogenic diet is a high fat, moderate protein, and very low carbohydrate diet.  The exact figures fluctuate from one person to the next, but a good ballpark is 80% to 85% of calories from fat, 10% to 15% of calories from protein, and 5% of calories from carbohydrates or “carbs”.

The Standard American Diet or SAD diet has a range of 40% to 60% carbs.  All of these carbs, whether they are fruit, or sweeteners like refined sugar, honey, high fructose corn syrup, and maple syrup, or complex carbohydrates like oatmeal, pasta, cookies, and brown rice eventually turn into blood sugar or glucose.  Our cells burn this glucose to make energy.  But our cells also have the ability to burn fatty acids for energy.  

Whenever we are primarily using fat as our energy source instead of sugar, we are in a state of nutritional ketosis.  Whenever we go without a meal for 12 hours or more, we go into ketosis as we burn our body fat.  Our Paleolithic ancestors ate and accumulated body fat during the summer and then lived off their body fat and were in ketosis during  the winter.  

By “starving” our bodies of glucose and providing lots of fatty acids to burn, we shift the energy pathways in our bodies to be very efficient at burning fats.