Calculation method for daily water intake components using doubly labeled water

This is the authors' abstract. We don't add key points for this paper.

Daily water intake (DWI) is essential for survival in humans; however, accurate assessment of DWI from drinks and beverages (Wdrinks) or food moisture (Wfoods) is difficult as it depends on self-reported intakes that are prone to inaccuracy. Here, we established an objective method to assess DWI components using doubly labeled water (DLW). Deuterium and H218O were orally administered, and the dilution space and elimination rate of 2H and 18O were measured. DWI was calculated from the deuterium turnover corrected for metabolic water production and insensible water absorption from humidity. Wfoods was estimated using dietary record (Wfoods-DR) or calculated from the total energy expenditure assessed by DLW (Wfoods-DLW). The current results underscore Wfoods-DR underestimation using self-reported dietary assessments, which underestimates food intake. This study proposes novel methods for calculating each DWI component using DLW.