What's the deal with protein?

I'm a fairly avid hiker. My dad took me on my first camping trip when I was only a few months old. My first backpacking trip was when I was three. And I even carried my own backpack. While growing up, my dad and brothers and I went backpacking in the Sierra Nevada. Last year I hiked to the top of Mt. Whitney, the tallest mountain in the lower 48 states. Just last weekend I hiked Mt. Nebo, the tallest in the Wasatch front, and will be reaching the summit of Kings Peak, the tallest in Utah later this summer. Through all of my hiking and talking with others about it, I tend to hear something that confuses me quite a bit. It has to do with protein. "Be sure to bring lots of protein."



Thanks for the responses from Claire, Rebekah, Kurt, and Marie. Here's more explanation on why I was confused about using protein during endurance activities – namely that it actually isn't a good energy source.