The net protein utilization, or NPU, is the ratio of amino acid converted to proteins to the ratio of amino acids supplied. This figure is somewhat affected by the salvage of essential amino acids within the body, but is profoundly affected by the level of limiting amino acids within a foodstuff.
Experimentally, this value can be determined by determining dietary protein intake and then measuring nitrogen excretion. One formula for NPU is:
NPU = ((0.16 × (24 hour protein intake in grams)) - ((24 hour urinary urea nitrogen) + 2) - (0.1 × (ideal body weight in kilograms))) / (0.16 × (24 hour protein intake in grams))
As a value, NPU can range from 1 to 0, with a value of 1 indicating 100% utilization of dietary nitrogen as protein and a value of 0 an indication that none of the nitrogen supplied was converted to protein.
Certain foodstuffs, such as eggs or milk, rate as 1 on a NPU chart.
You can combine proteins to get a NPU of one or even a little higher. Wheat gluten, and especially products like seitan made from gluten,
is ideal for this. A small amount of gluten can raise the NPU to 1 easily with a wide variety of vegetable protein sources. With cyclists, quality is more important than quantity.