PhotoChick - I'm trying to understand what you explained in your post.
Do you mean protein is excreted as in completely eliminated from the body?
I don't believe that's the case - a surplus of protein (when it comes to calories) is just like any other - if it isn't used, it becomes stored as fat in the body. The conversion of protein into adipose tissue is a more strenuous process than the conversion of fat into adipose, but it still happens.
When you say "Secondary to that is that our bodies have no mechanism to store protein for later use - what isn't used by your body is excreted." are you referring to the amino acids in the protein or the calories?
We know that the body's mechanism to store unused protein calories is just like with any other unused fat/CHO/protein calories - they are stored as fat if they are not used in glycogen or ATP production.
Also, you say
muscles are built of protein - absolutely true - but then you mentioned:
"if you're working your body hard, and you haven't eaten any (or much) protein at that point, your exercise will be less productive and your muscles will take longer to recover and to grow - because there are no
stores of protein to draw on."
- we have our muscles (built of protein) to draw from. It's not the best way to get by, but it is what the body resorts to when other energy sources become depleted.
I found some info on a website which supports what I'm saying:
"
Protein is broken down into amino acids in the stomach and small intestine, then distributed via the liver to cells throughout the body for a variety of uses included cell formation and repair. Some surplus protein amino acids are kept circulating in the bloodstream, the remainder is either converted into a type of simple sugar and used as energy, or (like carbohydrate) is converted to fatty acid and stored in adipose cells."
http://www.annecollins.com/body-fat-...ssue-guide.htm
I agree with you about the effectiveness of protein in controlling appetite - but I'm not sure that a lot of protein should be distributed in intervals throughout the day. For the average person, there's no need to fuel the body with protein more than 3 or 4 times a day, and if more than that - no more than small amount is really needed. (Obviously different depending on the individual's activity levels and lean body mass)
I also agree that athletic (and generally active) people absolutely need more protein so that their muscles have the ability to repair and recover. Sedentary individuals don't need as much, as they aren't having as much damage done to their muscles.
Upon reconsideration and taking into account what you said - I guess 120g isn't as much as I'd initially thought - but personally I find that I function pretty well on anywhere from 80 - 100 grams per day, and I'm a very active individual.
Of course, we're different and I respect that people have varying nutritional needs, but I just wanted to explain why the number you gave surprised me.