What Percent of Protein in Nuts "Count"?
I've read in various sources that only a certain percent of the protein in nuts and vegetables is absorbed by your body, even in the best of circumstances (something to do with it being bound up in a vegetable fiber matrix.).
Can anyone point to data saying what percent this is?
You can use the biological value (BV) of various protein sources as a general guide. Egg and whey are usually at the top of the list, but there is some debate with whey about how effective it actually is because it is digested so quickly and much of it may be converted to carbohydrates. Soy protein is also pretty high, significantly higher than most plant protein sources. Meat and dairy sources are also very high. Other plant sources like nuts, seeds, beans, legumes, vegetables, grains, fruits, etc. are generally quite a bit lower than the above sources. Many beans and whole grains are also high in phytic acid which blocks absorption of other nutrients. The phytic acid can usually be lowered through cooking, soaking, and/or fermenting. I'm not sure if this has an effect on protein bioavailibility though.
The BV is a measure of how much of the protein is digested and used for protein synthesize in an organism's cells. Again the BV is more of a general guide though, the true percentage various based on quite a few variables, including age, health, amount eaten at one time, cooking and preparation, nutritional state before eating (if you're in a starvation state it will be significantly higher), etc. Protein is the primary source of nitrogen in the body, so they determine the value based on much nitrogen is excreted in the urine and feces. The more nitrogen excreted, the less is being incorporated into proteins in the body.
It may be listed as a straight percentage, or a relative percentage may be show using egg as the standard. Egg has a BV of about about 93%. Other proteins are then adjusted and shown relative to egg protein. Egg is then set at 100% in these scales. This is why whey can be listed at over 100%. Obviously a percentage utilization of over 100% would be impossible, but relative to egg the scale can go over 100%.
You should check out the wikipedia page on BV for more information, it is pretty detailed.
Here are some biological values for some common foods:
whey, BV 104
egg, BV 100
cow's milk, BV 91
egg white, BV 88
beef, BV 80
fish, BV 79
chicken, BV 77
casein, BV 77
soy, BV 74
potato, BV 71
rice, BV 59
wheat, BV 54
beans, BV 49
peanuts, BV 43