In the absence of insulin, what happens to fats and proteins?

• A. They cease metabolism entirely
• B. They are stored as glycogen
• C. They are converted to glucose immediately
• D. They break down, releasing free fatty acids and leading to ketone body production.

Answer: (D)

When insulin is absent, the brakes on fat and protein breakdown are released. Fat cells undergo lipolysis, releasing free fatty acids into the blood, and muscles and other tissues break down proteins into amino acids. The liver then uses those fatty acids to produce ketone bodies, so fats and proteins are broken down rather than stored, and ketones are formed. This shift explains why lack of insulin leads to increased lipolysis and ketogenesis. The other scenarios don’t fit because metabolism doesn’t simply stop or store fats/proteins as glycogen in this state, and the breakdown into glucose isn’t an immediate, sole outcome without insulin; instead, ketone production becomes a key downstream result of unchecked fat oxidation in insulin deficiency.