Carbon and nitrogen isotopic ratios of urine and faeces as novel nutritional biomarkers of meat and fish intake

PURPOSE: Meat and fish consumption are associated with changes in the risk of chronic diseases. Intake is mainly assessed using self-reporting, as no true quantitative nutritional biomarker is available. The measurement of plasma fatty acids, often used as an alternative, is expensive and time-consuming. As meat and fish differ in their stable isotope ratios, δ(13)C and δ(15)N have been proposed as biomarkers. However, they have never been investigated in controlled human dietary intervention studies. OBJECTIVE: In a short-term feeding study, we investigated the suitability of δ(13)C and δ(15)N in blood, urine and faeces as biomarkers of meat and fish intake. METHODS: The dietary intervention study (n = 14) followed a randomised cross-over design with three eight-day dietary periods (meat, fish and half-meat-half-fish). In addition, 4 participants completed a vegetarian control period. At the end of each period, 24-h urine, fasting venous blood and faeces were collected and their δ(13)C and δ(15)N analysed. RESULTS: There was a significant difference between diets in isotope ratios in faeces and urine samples, but not in blood samples (Kruskal-Wallis test, p