As an endurance athlete, I've carefully strategized my nutrition during things like Ironman races and I'm thinking of extending it to mountain and hiking expeditions.

Previously in the Himalaya expeditions, we would carry dehydrated meals and melt snow to eat them but I think these mountain house backpacking meals are not ideal. Consider, a beef stew pouch, it's 190 calories, 22g carbs (3g as fiber), 6g fat, 13g protein with net weight of 49g and a cost of $6. But the bag itself weighs about an once = 28grams. Really you need to eat like 5 of these a day to get enough protein (60g) so it really takes up a lot of weight/volume. 5x190=950 calories

It's not bad but it takes a lot of room in your pack and I'd say it's kind of messy and the bag is quite heavy with about double the weight. In addition, I believe you do not need any fat nor fiber in short term high exertion times eg on the trail.

What I propose is an extreme diet which I'm sure I could maintain over a long weekend eg 3 days but will try 2 weeks to 30 days eg time spent in high camp.

I propose eating ONLY per day a total of 720 calories per day when travelling the equivalent of 25 flat miles/day:
3 pouches of Gatorade Recover Whey Protein (20g protein in 28g pack, 110 calories) = 360 calories
2 pouches of Gatorade Endurance (46g carbs in 49g pack, 180 calories) = 360 calories
1 multivitamin

These are extremely lightweight and pack down to nothing volume wise. They are immune to heat and require only cold water that can be obtained by melting snow or pumped from the stream.

In triathlon, it's known that you are able to digest only about 100-200 calories per hour max. At low exertion levels, eg below aerobic threshold, you can burn fat but high exertion levels you burn sugar and primarily the glycogen in your muscles.

Sipping Gatorade endurance the entire day will provide simple sugars for energy when needed eg during hard climbs. It's unlikely to climb more than 8hrs a day and that I estimate to be 50/50 fat/sugar as unlikely going to be above aerobic threshold. All the fat comes from your body obviously and that's free weight to carry.

Jogging around at 10 min miles (6mph) an 180 pound person burns about 820 calories/hr. So 25 miles in 4hrs = 3280 calories and add RMR of 1600 calories for a total burn of 4880 calories a day.

I think most people would only travel about the equivalent of half that eg 12.5 miles and burn only about 1600 calories in exercise and 1600 RMR for about 3200 calories. So you would be burning about 1.2 pounds of fat a day off your body (4160 calories) assuming you're doing the 25miles/day or 0.7 pounds a day of fat if you're doing 12.5 miles/day.

I believe your protein intake of 60g/day and 720 calories of sugar will keep your glcyogen stores sufficient to not deteriorate. As a bonus you should be burning some decent amount of fat and come back in better shape. 3 days say an average of 3 lbs fat loss or 7 pounds in a week is manageable. 30 days requires 30 lbs of fat which would be pushing it for most people but most people are around 25% body fat so 180lbs = 45 lbs of available fat. If you have close to a visible 6 pack then you probably have 15% body fat which would be 27 lbs available. If you are 10% body fat then you're looking like an extremely lean body builder but still have 18 pounds of available fat you can use and after a week would be down to 11 pounds which is still 6% body fat.

Anyway, to see how my body handles it I'll give it a shot for 3 days then move it to a week and see what happens.