INS and obesity due to melanocortin 4 receptor deficiency: Finally we confirmed the differential ability of insulin to stimulate glucose oxidation in obesity-associated versus obesity-independent tumor cells in studies of absolute glucose oxidation measured by trapping 14CO2 generated by oxidizing 14C6 glucose (Fig 2C): incubation with insulin doubles colon cancer cell glucose oxidation, while melanoma cells show no change in glucose oxidation rates when insulin is added to media.