Everyone has their bias on their diet and what they are willing to sacrifice for the goals and their well-being. In looking at what is for each individual, three major variables must be assessed. The first is you. What are you willing to do to accomplish your goals without sacrifice your health? What do we mean? Well, the three major macronutrients (carbohydrate, proteins and fats) all play similar and different roles in our internal biochemical lives in addition to how the taste in our mouths. All three can be used as energy, but only two are involved in growth, repair and development. Do you know which ones? To bias toward merely an energy source is potentially detrimental to the internal human processes. Are you will to allow your body to regularly break itself down without the proper building block to rebuild?
Second, the requirements to ingest carbohydrate constantly to maintain an energy level required by the activity can be quite challenging. To move toward a fat biased diet allows for fewer meals and a more constant energy level. This can offer two huge benefits. One is being able go longer without needing a break for rest or food, and your body maintains the constituents necessary to maintain a healthy physiological system negating the prior issue of your body breaking down.
The final variable is digestion of each macronutrient. As many know, carbohydrates break down and absorb quickly while fats, or lipids, take more time. So if you choose the fat path, then time must be taken in shifting toward this preference to allow the body to accommodate the change. Just like we have to train our cardiovascular and muscular system, we need to train our metabolic system to adapt to a new stress. Many chemical reactions take place to adjust to the demands of the metabolic world and efficiency is key long term.
With these three perspectives on fat or carb intake, I assume you see the bias. Fat plays a role in keeping the body healthy in the growth and repair department, but also in the high available energy need of mountain activities. The only challenge you need to take on is training your body to adjust to the needs of fat metabolism.