In obesity which of the following hormone levels is decreased ?
**Core Concept**
Leptin is a hormone produced by adipocytes that plays a crucial role in regulating energy balance and body weight by inhibiting appetite and increasing metabolism. Decreased leptin levels are associated with increased food intake and obesity.
**Why the Correct Answer is Right**
Leptin levels are inversely proportional to body fat mass. In obesity, the increase in body fat mass leads to a decrease in leptin production. This decrease in leptin levels contributes to increased hunger and reduced satiety, resulting in further weight gain. Leptin acts on the hypothalamus to inhibit the expression of neuropeptide Y (NPY), a potent stimulator of food intake, and increase the expression of pro-opiomelanocortin (POMC), a precursor to melanocortin-4 receptor (MC4R) agonists, which decrease food intake.
**Why Each Wrong Option is Incorrect**
* **Option A:** Insulin levels are often increased in obesity due to insulin resistance.
* **Option B:** Ghrelin levels are typically increased in obesity, as ghrelin stimulates appetite.
* **Option D:** Adiponectin levels are decreased in obesity, but this is not the correct answer.
**Clinical Pearl / High-Yield Fact**
Remember that leptin levels decrease in obesity, leading to increased hunger and reduced satiety, making it a key hormone in the pathophysiology of obesity.
**Correct Answer:** C.