The reason why is this is actually a more energy-efficient way of eating on trail (but not necessarily more practical), because lipids (fats) yield more energy per gram than carbs or protein (9 vs 4).
A small study was recently done on ultra runners and they found that the ultra runners who ate low-carb, high-fat diets actually burned MORE fat and had the same aerobic capacity as ultra runners who ate low-fat, high-carb diets. (
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The only drawback they found was that the low-carb runners did not have the energy for a big surge, or sprint. Fats burn more slowly from a metabolic standpoint and this can be a problem if you need to kick it into higher gear for a short time.
IMO, most hikers could benefit from a high fat, moderate protein, and low to moderate carb diet. You
do need carbohydrates if you are hiking, plain and simple; but I don't think we need as much as we think we do. A typical carby backpacker dinner should be enough. The rest of the day your body can utilize the stored glycogen from your dinner and the remainder of your energy will come from fats you consume throughout the day. Of course, you should eat protein every chance you get to mitigate catabolism of muscle tissue.
It's also worth noting that it takes your body some time to adapt to this diet. If you are a typical American who probably gets >60% of their daily calories from carbs, it will take a couple of weeks for your body to adapt to a lipid-dominant metabolism. But, it will be more efficient and you will effectively need to eat less frequently.