Steve, Carbs translate to sugar, which spikes blood sugar and requires insulin. The insulin will then store and protect your fat storage and prevent the fat from being used as energy. Fat is the supreme source of energy; several organs are dependent on fat to function properly.
Several clinical studies have been done using groups of outdoorsmen trekking through the wilds of Alaska. Some consumed hi-carb, moderate protein, lo-fat diets; others stuck to a hi-fat, hi-protein, zero carb diet. The results: the hi-carb group failed miserably and experienced periods of lo-mental capacity and severe atrophy (muscle loss). The hi-fat group experienced no atrophy and still had their wits about themselves. Remember, the human body is "stone-age" and has not changed since creation. The human body thrives on animal fat, animal protein, some nuts & seeds, and some fruit & vegetables when in season. Not until the advent of modern agriculture did the human body consume grains.
When in the back country, I pack jerky, pouches of fatty fish (tuna, salmon), macadamia nuts, almonds, and walnuts.