Serum ceramides have emerged as potential biomarkers of insulin resistance, diabetes, and heart disease. In this issue of Diabetes, Lemaitre et al.(1) report the largest longitudinal study to date correlating sphingolipids with insulin resistance, profiling a cohort of 2,086 American Indians at high risk for diabetes. With the analytical power that derives from profiling such a large number of samples obtained at two visits, 5 years apart, the data from the Strong Heart Family Study (SHFS) revealed that several ceramide species correlated with hyperinsulinemia and the HOMA of insulin resistance (HOMA-IR) in this at-risk population. Here, we summarize these results in the context of other preclinical and clinical studies investigating roles for ceramides as drivers of cardiometabolic dysfunction. Ceramides are central intermediates in the biosynthetic pathway that produces the large family of sphingolipids, which includes more than 4,000 distinct molecular entities. Much of the complexity in the cellular sphingolipid pool derives from the large number of acyl chains that can be incorporated into the ceramide scaffold. Over the past 20 years, a large number of studies in preclinical models suggest that ceramides may be among the most pathogenic nutrient metabolites that accumulate in obesity, linking overnutrition to insulin resistance and its sequelae of comorbidities. In cultured cells or isolated tissues, ceramides inhibit insulin signaling and action and inhibit lipid oxidation (2). In rodents, numerous ceramide-lowering interventions have been shown to improve insulin sensitivity and ameliorate diabetes and cardiovascular pathologies (2). Because of these data, a handful of companies have started to develop ceramide-reducing interventions in hopes of producing insulin-sensitizing therapeutics. Despite the strongly consistent findings obtained in preclinical models, the role of ceramides in human cardiometabolic pathologies has been controversial. The debate stems largely from discordance in lipidomic profiling studies, as ceramides in muscle or liver biopsies have been reported to be changed in some, but not all, insulinresistant subjects (3–5)(Fig. 1). As these discrepant studies typically involved relatively small subject numbers, studies such as the one by Lemaitre et al.(1) are informing the debate. Lemaitre et al. profiled 15 sphingolipid species in a large cohort of Native Americans without diabetes (average age of 38 years), 24% of whom had a BMI of 35 kg/m2 or greater. Those participants with twofold higher (90th percentile) ceramide with 16: 0 (Cer-16), Cer-18, Cer-20, or Cer-22 displayed hyperinsulinemia and insulin resistance (estimated using HOMA-IR, a measure of insulin resistance determined from fasting glucose and insulin concentrations). Indeed, those with twofold higher baseline concentrations of Cer-16 had 14% higher levels of insulin, revealing the increased insulin needed to maintain euglycemia owing to the insulin insensitivity. These studies are consistent with earlier, smaller studies evaluating relationships between serum ceramides and insulin resistance in both humans and nonhuman primates (6–10). However, this new study distinguishes itself from the prior ones because of 1) the large size of the cohort, 2) the novel population surveyed, and 3) the longitudinal nature of the analysis (ie, 5-year follow-up). Insulin resistance is a major risk factor for diabetes and cardiovascular disease, and the findings of Lemaitre et al.(1) are interesting to consider in relation to other recent studies evaluating relationships between ceramides and clinical indices of cardiometabolic dysfunction. For example, Wigger et al.(11) identified relationships between …