Lack
of accurate dietary assessment in free-living populations
requires discovery of new biomarkers reflecting food intake qualitatively
and quantitatively to objectively evaluate effects of diet on health.
We provide a proof-of-principle for an analytical pipeline to identify
quantitative dietary biomarkers. Tartaric acid was identified by nuclear
magnetic resonance spectroscopy as a dose-responsive urinary biomarker
of grape intake and subsequently quantified in volunteers following
a series of 4-day dietary interventions incorporating 0 g/day, 50
g/day, 100 g/day, and 150 g/day of grapes in standardized diets from
a randomized controlled clinical trial. Most accurate quantitative
predictions of grape intake were obtained in 24 h urine samples which
have the strongest linear relationship between grape intake and tartaric
acid excretion (r<sup>2</sup> = 0.90). This new methodological pipeline
for estimating nutritional intake based on coupling dietary intake
information and quantified nutritional biomarkers was developed and
validated in a controlled dietary intervention study, showing that
this approach can improve the accuracy of estimating nutritional intakes
