APLN and obesity due to melanocortin 4 receptor deficiency: Therefore, in future studies, it will be necessary to examine changes in apelin-12 and apelin-36 concentration in obesity, diabetes, and metabolic syndrome patients, after changes in physical composition via dietary regulation, a combination of exercise and dieting, or exercise only and to compare changes in physical composition and exercise performance of men and women of different age groups to examine whether there are any differences in the effects of apelin.