This 'new' diet for runners emphasizes more protein, more fat, and fewer carbohydrates so the body becomes more efficient at fat burning.

It's all about balance. There are many benefits to teaching your body to work a little harder with less fuel, but this can also create a lot of stress on the body and should not be used week after week for a long period of time. As with all diets, everything depends on the individual. Someone who metabolizes meat very efficiently as a fuel would do better on a metabolic efficiency diet, while plant-based eaters would struggle to get the correct balance of protein to carbohydrate and would have to supplement their protein.