查看文章

Seasonal reductions in food availability may cause animals to catabolize endogenous tissue and the resulting loss of lean mass can hinder their ability to forage and reproduce. While several studies have considered nitrogen isotopes (δ¹⁵N) as an indicator of catabolism, relationships between protein intake, body condition, and tissue δ¹⁵N have not been assessed simultaneously in controlled conditions. We conducted a feeding experiment on laboratory mice (Mus musculus) to test the effects of low (5%) versus high (30–40%) dietary protein content on lean mass, fat mass, and tissue δ¹⁵N. This approach enables the distinction between use of exogenous and endogenous nitrogen, illuminating a framework of protein metabolism and tissue synthesis. As expected, lean mass and body fat were lower in mice fed low-protein diets. Nitrogen isotope discrimination (Δ¹⁵N) between blood plasma-diet and liver …