Effect of Organic Food Intake on Nitrogen Stable Isotopes

Abstract

Food choices affect the isotopic composition of the body with each food item leaving its distinct isotopic imprint. The common view is that the natural abundance of the stable isotopes of nitrogen (expressed as δ15N) is higher in animals than in plants that constitute our contemporary diets. Higher δ15N is thus increasingly viewed as a biomarker for meat and fish intake. Here we show that organic compared to conventional farming increases plant δ15N to an extent that can appreciably impact the performance of δ15N as a biomarker. The error that can arise when organic plants are consumed was modelled for the entire range of proportions of plant versus animal protein intake, and accounting for various intakes of organic and conventionally grown crops. This mass balance model allows the interpretation of differences in δ15N in light of organic food consumption. Our approach shows that the relationship between δ15N and meat and fish intake is highly contextual and susceptible to variation at the population, community or group level. We recommend that fertilization practices and organic plant consumption must not be overlooked when using δ15N as a biomarker for meat and fish intake or to assess compliance to nutritional interventions.

Differences in the Levels of the Selected Phytoestrogens and Stable Isotopes in Organic vs. Conventional Hops and Beer

“…No statistically significant difference was observed in the δ 13 C values (average −26.7 ± 0.8‰) between conventionally and organically produced hops. However, δ 15 N values in European samples were lower than the organically produced hops [24].…”

“…Thus, organic plant products vary within a range of δ 15 N values of +0.3 to +14.6‰, while conventional plant products range from negative to positive values, i.e., −4.0 to +8.7‰ [22]. Literature data presented by Mantha et al [15] indicate that the mean δ 15 N value of organically grown plants of 7.7 ± 4.4‰ (median = 7.2‰), while it was 2.8 ± 2.3‰ (median = 3.0‰) for plants fertilised inorganically, resulting in a δ 15 N org-conv of 4.2‰. The stable isotopes of carbon (δ 13 C values) can also act as an indicator of crop management practice.…”

“…Among the lighter elements having two or more stable isotopes (H, C, N, O, S), the stable isotopic composition of nitrogen (δ 15 N values) has been used to differentiate between conventional and organically produced crops [15][16][17][18].…”

“…where δ * X refers to δ 13 C, δ 15 N, while * X/X are the ratios 13 C/ 12 C, 15 N/ 14 N of the sample, and an international reference standard. Analyses were calibrated against the following international standards: USGS64 (glycine, δ 13…”

“…In addition to commercial fertiliser, soil organic matter, manure, cover crops and returned hop vines can supply substantial N for hop production and influence the δ 15 N values. It is interesting to note that the highest δ 15 N values in EU hops originate from the Czech Republic, one of the largest hop producers in the world (26). No statistically significant difference was observed in the δ 13 C values (average −26.7 ± 0.8‰) between conventionally and organically produced hops.…”