A Ketogenic Diet or LCHF diet is a low carb, moderate protein and high fat diet which turns the body into a fat burning machine. By restricting carbohydrates to 20 grams or less a day the body goes into a metabolic state known as Ketosis. Ketones are produced in the liver from fat and are then used as fuel throughout the body and brain.
On a Ketogenic Diet your entire body switches its fuel source from sugar to fat. Insulin levels become very low and burning fat increases resulting in weight loss and stable blood sugars.
I recommend listening to:-
Dr Eric Westman 'The Science Behind Keto Lifestyles' - https://youtu.be/9OFY10WjUaY