However, the degree of insulin resistance does not always correlate with the extent of obesity (Gan et al., 2003) and there exists a population of individuals who are obese yet exhibit no difference in insulin action compared to groups of lean individuals (Tonks et al., 2016), and lean individuals who are metabolically unhealthy (Stefan et al., 2017). Here, INS is linked to obesity due to melanocortin 4 receptor deficiency.