Desirable Diet to Lower the Japanese Nitrogen Footprint: Analysis of the Saitama Prefecture Nutrition Survey 2017.

With the growing interest in healthy and sustainable diets, studying diets with high nutritional quality and low environmental impact is needed. We focused on the nitrogen footprint (NFP)-an indicator of reactive nitrogen loss that causes various environmental impacts-of Japanese diets using individual dietary records and identified the characteristics of lower NFP diets. This cross-sectional study was a secondary data analysis from the 2017 Saitama Prefecture Nutrition Survey. We analyzed the data obtained from a questionnaire and two-day dietary records of 479 men and women aged 30-65 y who had no misreported or missing data. The NFP was calculated using the virtual nitrogen factors of each food group reported in a previous study. After assessing NFP and its contributions, we conducted sub-group analysis for participants with appropriate weight status and adequate protein intake, classifying them into three groups according to tertiles of NFP to protein ratio. We compared NFP, its contributions, and nutrient intake between the groups. The total NFP (kg N/y) was 18.2±5.0 in men and 16.1±4.4 in women. In the sub-group analysis, total NFPs of the lower NFP group were 16.5±3.1 in men and 13.6±2.8 in women. Cereals, pulses, and fish and seafood contributed more significantly to the total NFP in the lower NFP group than in the higher NFP group. These results suggest that adequate protein intake from a variety of food sources is required to lower the environmental impact of adequate diets.