However, in a study by Knudsen et al. [21] of women divided into three groups: with obesity, normal-weight with sedentary habits (controls), and endurance athletes, the endurance-trained women had significantly higher IL-13 levels but lower IL-6 levels than obese women, who had higher IL6 levels than the controls. Here, IL6 is linked to obesity due to melanocortin 4 receptor deficiency.