Student or Learner
I would like to know what "able" refers to? Who/what is able to balance daily nitrogen losses?
Determination of the nutritional efficiency of protein in the diet is in most cases based on estimating the extent to which dietary protein nitrogen is absorbed and retained by the body and is able to balance daily nitrogen losses. Net Protein Utilisation (NPU) is the percentage of ingested nitrogen that is retained in the body, and the Biological Value (BV) gives the percentage of absorbed nitrogen that is retained.
I think 'dietary protein nitrogen' is the subject of 'is able to ...'.
I am not a teacher.