Final answer:
In obesity, there is often a decreased sensitivity to leptin, a condition known as leptin resistance, which disrupts the normal satiety signals to the brain, leading to overeating and weight gain.
Step-by-step explanation:
The effects of leptin and its levels in the context of obesity can be explained by the phenomenon known as leptin resistance. Normally, leptin is a hormone produced by adipose tissue, and it signals to the brain to induce satiety after eating. However, with obesity, individuals often exhibit a decreased sensitivity to leptin. As a result, even though fat cells may be secreting high levels of leptin, the brain does not receive the satiety signal effectively. Therefore, the correct answer to what happens to leptin levels and its effects with obesity is: C) With obesity, the brain becomes resistant to the satiety effects of leptin. People with leptin resistance continue to eat beyond their energy needs, which can exacerbate weight gain and contribute to the further development of obesity.