Final answer:
The correct statement about leptin is that few cases of human obesity are related to a mutation of the gene for leptin and leptin receptors. Leptin is a hormone that helps regulate appetite and energy balance by inhibiting hunger, and it plays a role in reproductive health as well.
Step-by-step explanation:
The true statement about leptin among the options given is: 'Few cases of human obesity are related to a mutation of the gene for leptin and leptin receptors.' Leptin is a hormone produced mainly by fat cells that normally inhibits appetite by inducing a feeling of satiety. It is secreted by adipose tissues in response to food consumption and helps to regulate energy balance by inhibiting hunger, which in turn diminishes fat storage in adipocytes.
Contrary to the second statement, leptin levels generally increase during overeating and are higher in obese individuals due to the larger amount of adipose tissue present, although these individuals may exhibit leptin resistance. Leptin levels are indeed related to body fat content in both obese and non-obese individuals. Lastly, while genetic factors do play a role in obesity, mutations in the leptin gene are relatively rare causes of the condition. Leptin's function extends beyond appetite regulation. For instance, adequate leptin signaling is necessary for the synthesis of gonadotropin-releasing hormone (GnRH) and gonadotropins, which are essential for reproduction. This highlights leptin's role in maintaining various physiological processes, including reproductive health.