Interestingly, when both Sprague-Dawley rats and Long-Evans rats were maintained on a high-fat diet, only Long-Evans rats gained significant body weight and exhibited hallmarks of obesity (e.g. increased body fat, plasma leptin and insulin, etc.)despite the fact that both Sprague-Dawley and Long-Evans rats displayed enhanced pain sensitivity (Song et al., 2017). This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.