There is a reason why we store hundreds of thousands of calories in the form of fat in our body and only about 2000 calories in the form of glucose (with only a small amount of this useable by the brain). The reason is simple - The body prefers fat as its fuel source. Mark Sisson explains this in his article ‘A metabolic Paradigm Shift, or Why Fat is the Preferred Fuel for Human Consumption’.
Low carb, high fat diets have been used for centuries by doctors when working with obese patients. William Banting published the widely popular booklet titled ‘Letter on Corpulence Addressed to the Public’ in 1863. In this booklet he explained how he had slimmed down by eating a diet high in fat void of carbs. The Banting diet was used for decades by individuals looking to lose weight.