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Why can diabetes mellitus cause hunger, weight loss, and weakness?

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An anatomical illustration of the human pancreas shows its location near the stomach and intestines, a detailed cross-section highlighting ducts and the islet of Langerhans, and an inset of pancreatic tissue histology with labeled alpha, beta, and delta cells. — diabetes mellitus The islets of Langerhans are responsible for the endocrine function of the pancreas. Each islet contains beta, alpha, delta, and pancreatic polypeptide (PP) cells that are responsible for the secretion of pancreatic hormones. Beta cells secrete insulin, a well-characterized hormone that plays an important role in regulating glucose metabolism.

In diabetes mellitus, the body either fails to produce enough insulin or becomes resistant to its effects. Insulin is essential for signaling cells to take up glucose from the blood to use as energy. When this process is impaired, cells are effectively starved of their primary fuel source despite high levels of sugar circulating in the blood.123

This metabolic dysfunction leads to the following symptoms:

Hunger (Polyphagia): Because cells cannot access the glucose they need for energy, the body signals a state of "cellular starvation," which triggers an increased appetite.3
Weight Loss: Unable to utilize glucose efficiently, the body begins to break down its own fat and muscle tissue for energy. Additionally, the loss of glucose through urine represents a significant loss of calories that the body cannot retain.32
Weakness: The inability of cells to properly metabolize glucose, combined with the breakdown of muscle tissue and the loss of fluids through frequent urination, results in significant fatigue and physical weakness.3

These symptoms are direct consequences of the body's inability to maintain proper energy homeostasis due to insulin deficiency or resistance.12