The study examines the sources of variation in consumer-diet δ15N enrichment, a key parameter used to infer trophic relationships in ecological studies. Through a meta-analysis of 134 estimates from controlled studies, the authors identify several significant factors influencing δ15N enrichment. These include the biochemical form of nitrogen excretion (ammonotelic, ureotelic, or uricotelic), diet type (plant, animal, or manufactured mixtures), taxonomic class (molluscs and crustaceans generally showing lower enrichment), and environmental factors (marine environments yielding lower enrichment). The C:N ratio of the diet also significantly affects δ15N enrichment, with nitrogen-poor diets having a similar effect to fasting. The study highlights the importance of considering these variations in statistical approaches for studying diet and trophic relationships.The study examines the sources of variation in consumer-diet δ15N enrichment, a key parameter used to infer trophic relationships in ecological studies. Through a meta-analysis of 134 estimates from controlled studies, the authors identify several significant factors influencing δ15N enrichment. These include the biochemical form of nitrogen excretion (ammonotelic, ureotelic, or uricotelic), diet type (plant, animal, or manufactured mixtures), taxonomic class (molluscs and crustaceans generally showing lower enrichment), and environmental factors (marine environments yielding lower enrichment). The C:N ratio of the diet also significantly affects δ15N enrichment, with nitrogen-poor diets having a similar effect to fasting. The study highlights the importance of considering these variations in statistical approaches for studying diet and trophic relationships.