Even that 132 lb. woman will burn a lot more calories if she's backpacking, say, 10 miles per day at 10,000 feet altitude. Unless she is fully acclimatized to the altitude (takes at least a month), she will burn a lot more than 2,000 calories per day even without the additional activity. The same is true for the increased activity without the altitude. Put the two together, and she probably can't eat enough to maintain her weight.

I try to plan for 1 lb. of food per day for trips of a week or more. For those longer trips, I try to pick lighter weight food, such as freeze-dried fruit, instead of dehydrated, for snacks and lunches. Of course, it's more expensive, so for trips of a few days I use dehydrated to save money, which means more like 1 1/4 lbs. of food per day. For an overnighter, I may even take fresh food, which is heavier yet. On the other hand, for the first few days of a trip, my appetite tends to be poor.

Of course I am one of those "perpetually plump" people who can always stand to lose some pounds, so I don't worry about being undernourished.

If you must live on a "Mountain House" diet, and don't need to lose weight, do remember that it is extremely low in fat, which is the most efficient source of calories (9 calories per gram vs. 4 for protein and carbs). Taking along some olive oil and adding a tablespoon or two to your freeze-dried dinner when rehydrating will boost your calorie count, and it will probably taste better. If you don't want to decant olive oil into a plastic squeeze bottle (note that it may leak, so keep the bottle in a ziplock bag), you can buy envelopes of a pretty good olive oil from minimus.biz. And it's really healthy fat.

And, of course, there's always peanut butter!

One thing to note is that dehydration destroys vitamin C. For trips of a month or more, you might want to plan on taking a supplement.