**Core Concept**
During prolonged fasting, the body undergoes significant metabolic adaptations to maintain homeostasis. The hypothalamic-pituitary-adrenal axis is activated, leading to the release of stress hormones such as cortisol and growth hormone (GH). GH plays a crucial role in mobilizing energy stores and promoting lipolysis.

**Why the Correct Answer is Right**
In a state of prolonged fasting, the body's energy stores are depleted, and the need for energy mobilization increases. GH levels typically increase in response to fasting, promoting lipolysis, gluconeogenesis, and glycogenolysis. This increase in GH helps to maintain blood glucose levels and mobilize energy stores. Therefore, GH levels are expected to **increase** during prolonged fasting, making option A incorrect.

**Why Each Wrong Option is Incorrect**
**Option B:** Glucose tolerance decreases during prolonged fasting due to the depletion of glycogen stores and the impaired ability to mobilize glucose from stored sources.
**Option C:** Immunoreactive insulin levels decrease during fasting due to the low glucose levels and the suppression of insulin secretion.
**Option D:** Free fatty acids (plasma) increase during fasting due to the mobilization of triglycerides from adipose tissue, which is stimulated by hormones such as GH and cortisol.

**Clinical Pearl / High-Yield Fact**
During prolonged fasting, the body's ability to mobilize energy stores is impaired, and the risk of hypoglycemia increases. GH levels typically increase in response to fasting, making it an important hormone for energy mobilization.

**Correct Answer:** **✓ Correct Answer: A. GH levels decreased**