This is what I've learned about protein intake:
http://waltonfeed.com/omega/protein.html
Introduction: It's easy to get all the protein we need without eating meat. While it is not easy or inexpensive to store meat, plant protein can be stored very economically for a long time.
Points to remember about protein:
1. The RDA of protein for a 79kg (174 lb.) adult male is about 63 Grams. Women (calculated for a 63kg or 138 lb. woman) need about 50 grams. (0.8 Grams protein per Kilogram of body weight.) Pregnant and nursing women require about 30% more. Children need as much as adults because they are growing. A rapidly growing child can require 2 to 3 times more protein than an adult by weight.
2. A safety factor was built into the RDA for protein and actually represents a little over twice as much as our bodies actually need.
3. Our body gets all but 1/6 of the protein it needs from recycling old body tissue. This amounts to 100-300 grams. The 1/6 we don't recycle must come from essential amino acids we eat.
4. Hard work does not require more protein!
5. Protein is required for growing, body repair, and maintenance. A person with serious physical injuries or illness requires much more protein.
6. If we do not get enough protein, our bodies will steal it from our muscles. This is also true when we are ill. We need more protein, but often can't eat it.
7. North Americans generally eat 3 to 5 times more protein than they need. The protein not needed is broken down further and most of it is used to make energy. However there is some left over product from this process which is not good for our bodies.
8. We can only absorb about 25 grams of protein at one time. The rest is broken down and burned or stored as fat.
9. Plant protein is absorbed at about 70-90%, animal protein at 85-100%. There is concern among some about plant protein not being absorbed as readily as animal protein. This is not a problem as we in North America presently eat 2 to 3 times the RDA for protein anyway.
10. North Americans have been brain washed into believing they must get their protein from meat. Third world nations all over the globe, who get enough calories in their diets, eat little or no meat yet many of them are in excellent health from eating only plant protein.
11. Men require about 2900 calories and women require about 2200 calories per day. Hard work requires more.
12. Our bodies digest the proteins we eat, separating them into amino acids which are absorbed into our blood stream.
13. Our bodies use 22 amino acids to make 50,000 different proteins we must have to be healthy.
14. Our bodies can make all but 8 of these amino acids. The 8 amino acids it can't make are called essential amino acids, as we must get them from the foods that we eat.