LEPR and diabetes mellitus: Knowing that the variability of in vivo isotopic signatures is an index of combined effects of the diet (e.g. natural enrichment via ingested carbon sources), and other inherent variability related to physiology, we compared the natural abundance isotope ratio of rats that spontaneously develop diabetes (ZDF-Lepr fa/Crl; ZDF (fa/fa)) and their non-diabetic littermates (ZDF fa/+) fed the same diet (Figure 1).