Stable isotope ratios potential use in nutritional epidemiology

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1 Stable isotope ratios potential use in nutritional epidemiology Gunter G. C. Kuhnle Department of Food & Nutritional Sciences University of Reading

2 Outline Background to stable isotope ratios isotopic fractionation and enrichment, biochemical processes etc Application of stable isotope ratios in ecology and archaeology Technical considerations bulk and compound specific analyses Current applications as biomarkers Bulk analysis (e.g. in EPIC Norfolk, Yup ik) Compound specific analyses - alanine-d 13 C as example for sugar intake Outlook and future applications

3 Stable isotopes and abundances

4 Isotopic fractionation and stable isotope ratio Occur because of differences in energy required for physical/chemical reactions δ n X = [δ n X Sample δ n X Standard ] / δ n X Standard 1000 Chemical reactions e.g. C4 vs C3 plants RuBisCo discriminates against 13 C δ 13 C lower in C3-plants C4-plants e.g. maize, sugar cane, millet, sorghum Ribulose-1,5-bisphosphate-carboxylase-oxygenase

5 Photosynthesis and stable isotope ratios C4 δ13c C3 Maize Millet Sorghum Sugar cane

6 Isotopic fractionation and stable isotope ratio Physical processes evaporation/condensation (enrichment of 18 O/deuterium) large differences between water sources 'heavier' near coast/equator, lighter NASA

7 Isotopic fractionation Trophic level Nitrogen metabolism affects δ 15 N 15 N retained, 14 N excreted Animal protein 15 N enriched

8 Stable isotope ratios summary of applications

9 Main stable isotope ratios in human nutrition δ 13 C Type of photo-synthesis (C3/C4) Position in food chain per trophic level Typical C&N isotopic values for Europe 20 SEA MAMMALS 15 FISH &SEA-BIRDS δ 15 N Position in food chain +3-4 per trophic level δ 15 N ( ) 5 C3 PLANTS C3 CARNIVORES C3 HERBIVORES 0 N 2 -FIXERS C4 PLANTS δ 13 C ( ) diet to bone collagen

10 Stable isotope ratios and dietary assessment vegan Oxford residents hair German vegetarians in Berlin (hair) 8.0 δ 15 N ( ) ovo-lactovegetarian omnivore δ 15 N 7.5 Ovo-Lacto-Vegetarian Vegan Animal protein intake δ 13 C O Connell & Hedges AJPA 1999 Petzke, Boeing & Metges RCMS 2005

11 Stable isotope ratios in nutritional epidemiology Intake of EPA and DHA Intake of sugar-sweetened beverages δ 13 C Low intake Davy et al. JADA 2011 High intake O Brien et al. AJCN 2009

12 Intervention studies for biomarker validation Vegetarian/Meat/Fish Biofree n=14 Controlled environment High meat (326 g/d) High fish (375 g/d) Meat/Fish (Vegetarian n=4) 8 days Blood, urine & faeces n=11 Controlled environment Controlled habitual diet 30d Daily blood, urine & faeces

13 Dietary intervention study Kuhnle et al. EJN 2012

14 Different specimen In humans Protein turnover (e.g. albumin) RBC

15 Habitual diet δ 13 C δ 15 N Plant food intake (g/g)

16 Habitual diet Biofree 1 study 11 participants Controlled habitual diet

17 Stable isotope ratios diet and metabolism? δ 15 N normalised to pre-conception values ( ) Conception Birth δ 15 N error = Decrease by weeks but variable Estimated weeks since conception (Birth weeks) Fuller et al., RCM, 2005

18 Starvation and δ 15 N Mekota et al., RCM, 2006

19 Results from EPIC δ 13 C and δ 15 N positively correlated with fish intake δ 13 C correlated with animal protein δ 13 C inversely associated with diabetes δ 15 N positively associated with diabetes Other findings Smoking positive correlation with δ 13 C and δ 15 N Alcohol intake positive correlation with δ 13 C Patel et al., AJCN, 2014

20 Compound specific stable isotope ratios δ 13 C Alanine NEAA synthesised from glucose Choy et al., JN, 2013

21 Stable isotope ratios complex marker, complex information Fate of individual compounds Carbohydrates Energy Proteinogenesis Lipogenesis Proteins Storage/Anabolism Energy N-excretion via citric acid pathway Diet Metabolism Fat Storage Energy Urine Blood Hair