I used to wonder about this diet also. it seemed to make sense to me that using both energy sources at the same time was excess energ. I then asked Dave Pulumbo is his opinion of keeping fats and carbs seperate as fuel sources and his response was that Protein and fat were responsible for building muscle and therefore should be included in every meal. Carbs are used to fuel the process so they should be used as needed. No need to seperate for muscle growth. For fat loss he suggested cutting carbs altogether. I dont agree with everything he says but hes right on the money the majority of the time.