I have been lifting weights recently so protein and growth have been on my mind.
I was reading about the composition of human breast milk ( http://en.wikipedia.org/wiki/Human_breast_milk#Composition ). I was a bit surprised because it doesn't have as much protein as I thought it would since babies grow so fast during the breast-feeding stage. What implications might this have for an adult seeking to build muscle?
Protein is but one building block. A simple explanation (not totally accurate, but gets the point across) is that protein "fills up the muscles". That is, a weightlifter doesn't really make new muscle cells (no one does), the protein just makes them bigger and stronger. A growing baby is actually making new cells (and quite rapidly), and the building blocks of cells (cell walls) are primarily saturated fat and cholesterol, which breast milk is quite rich in.
This is covered in Perfect Health Diet. Here is one article for you from the blog - http://perfecthealthdiet.com/?p=2712
This was, in part, their basis for 20% carbs, 15% protein, 65% fat. For adults they essentially double the protein and take half the carbs in breast milk as one way to "justify" their optimal levels. There were other aspects of their ratio justification in the book.
I have posted this before here on PH - I think most people overestimate their protein requirements. The answer your question is one does not need nearly as protein as conventional wisdom suggests. The old 1 g/lb bodybuilder mantra seems to die a hard death like the Diet-Heart Hypothesis.
EDIT - Page 9 in PHD covers this in "Human Breast Milk and the Adult Diet" section - "How will the optimal adult diet differ from an infant's? The brain is the body's primary consumer of carbs, and the brain accounts for 50% of calorie consumption in infants, but only 20%...in adults. Since adults require less than half the carbs that infants do, the optimal adult carb intake is likely about 20% of total calories rather than the 39% of infants. Starting from human like ratios (39%C, 54%F, 7%P), and changing half the carb calories to fat and protein, we get a ratio of 20% carb - 64% fat - 16% protein.
Other quotes from the book on Page 24
I am NOT vehemently asserting that PHD is the gospel, just giving you a relatively popular Paleo source for your consideration.
Anthropologist John D. Speth has written a lot on the issue of protein. The protein needs for a fetus and an infant, and even gestating mother, are surprisingly low and higher levels of protein might even be toxic. Pregnant hunter-gatherer women generally eat low-protein diets. Goes to show that our association with protein and growth is not as neat as it seems. It als goes to show that life stage matters quite a bit in human nutritional needs.
You're right, milk isn't a good idea. Babies develop primarily because of the hormones and fat in milk, not protein. Milk for adults is completely unnecessary and even damaging; stick to quality lean meat for your protein needs.
For more info on cutting out dairy: http://whole9life.com/2009/07/dairy-manifesto/