On Sat, 12 Jan 2002 14:02:34 -0000, Peter Smith <[log in to unmask]> wrote: >I am unsure whether the upper limit to avoid protein toxicity is >absolute, percentage, or of some other type. If it is a limit on >percentage of calories obtained from protein (as opposed to a fixed >number of grams of protein per day), then someone who takes in >sufficient calories to support a large muscular body and a >strenuous life can eat a larger number of grams of protein per day >than a slender sedentary person who takes in fewer calories. Codrain said that protein toxicity arises by the inability of the body to upregulate the urea synthesising enzymes above a certain limit. Urea is built for the purpose to excrete the excess nitrogen from the unused (or better used calorically) amino acids. This capacity would be determined by the size of organs who do the job. Liver and kidney. The process is nicely described in http://www.zonehome.com/met/metprotnit.htm If the excess nitrogen cannot be excreted, toxicity arises. In addition to the urea synthesis capacity also the kidneys have to have enough excreting capacity for the urea. If urea cannot be excreted fast enough it would likewise cause toxicity. In a high protein diet of living material (milk is nor living) the cells eaten also contain cell kernels, with the DNA (genetic material). In humans (as opposed to cats) this excess DNA also has to be excreted (it's called purines). A job wich requires additional work by the kidney. Animal protein tends to have more DNA in it than plants because animals have more genetic information - they are complexer. Very rapidly growing tissues also have more DNA. This is the case for fish skin, and organs. Or generally the stuff not recommended for gout. Then in degrading the protein also the problem of ammonia toxicity for the brain will come up (described in the same paper in point 3. a recommended reading on the topic). The symptoms "if the brain becomes deprived of its source of ATP" (energy) should be similar to those of hypoglycemie (low blood sugar). In short, the absolute amount of protein is what matters or limits. For example Australian aboriginals, which were reported to temporarily eat some 75 percent of calories as protein, did so with a diet of only 1000-1200 kcal. If you eat so little energy, the protein percentage can be high. If you eat a high calorie diet (>2400 kcal) the protein energy percentage is to be lower. I think that the organs involved can be trained to increase the absolute amount by becomeing enlarged, to a certain extent. In any condition of problems in the liver or the kidney I think it would be a bad idea to eat protein up to the limits. regards, Amadeus S.