I have heard a much more conservative amount of 30 to 50 grams for the average adult. The problem (as I understand it) it that to much protein, and especially the super concentrated protein in animal products, leads to calcium loss in the bones. I guess when your body breaks down the protein, it is turned into an acidic substance, which then leaches out the calcium. I think it is called Hypercalciuria, which translates in to too much calcium being lost through the urine. This is all hearsay, but it certainly makes sense. There are numbers to back it up. America and some european countries have the highest dairy and meat consumption of all countries, but also suffer the highest incedence osteoporosis, while countries with virtually no dairy and meat in thier diet have the lowest. This is all gleaned from an interview with Dr. Michael Klaper, who is an MD who strongly supports vegan lifestyles.