Figure 7.

The nitrogen “gap: in rats. A “nitrogen gap” was found when analyzing all the components of the nitrogen balance in young rats: i.e., the N ingested, that excreted by urine and feces as well as the total N accrued, thus proving the existence of a sizeable part of the N excreted not as urea, or through the other possible ways and means shown in Box 1. Different complete (measuring both sides of the N balance equation) studies repeated these findings, dependent on diet, and with a magnitude (in rodents at least) in the range of 10–30% of all nitrogen excreted. Redrawn with data from Esteve et al. [130].