Estimation of nitrate metabolism in intestinal tract by measuring breath nitrous oxide concentration in Chinese and Japanese.

We have previously reported that ingestion of vegetables containing high nitrate (NO3-) increases breath nitrous oxide (N2O) concentration, probably due to denitrification. In the present study, we estimated NO3- metabolism in the intestine by determining exhaled breath N2O concentration after the ingestion of vegetables by 16 healthy Chinese and Japanese. Breath samples were collected at 15-min intervals for 4 hr after subjects ingested 180 g of vegetable juice or 50 g of lettuce. Breath N2O concentration was measured by an IR-PAS analyzer. Lettuce but not vegetable juice increased N2O concentrations similarly in Japanese and Chinese. In control subjects who ingested nothing, there were significant differences between Chinese and Japanese in peak N2O concentrations (334 +/- 91 vs 140 +/- 24 ppb, P = 0.027) and total excretions (535 +/- 143 vs 214 +/- 36 microg, P = 0.036). Although the reason for this difference is unclear, Chinese subjects could produce breath N2O from other metabolic pathways than denitrification of dietary NO3.