Which metabolic state is associated with very low carbohydrate intake, typically around 50 g/day?

• A. Glycolysis
• B. Gluconeogenesis
• C. Lipogenesis
• D. Ketosis

Answer: (D)

Very low carbohydrate intake around 50 g/day shifts the body's energy use toward fat, with ketone bodies becoming a major fuel. When carbs are scarce, insulin drops and liver glycogen becomes depleted. Fat is released from adipose tissue and sent to the liver, where it is broken down into acetyl-CoA. Because oxaloacetate is held up by gluconeogenesis and not readily available for the TCA cycle, acetyl-CoA is channeled into producing ketone bodies (such as acetoacetate and beta-hydroxybutyrate). These ketones circulate and can fuel many tissues, including the brain, defining a state of ketosis. The other processes describe different situations: glycolysis uses glucose from carbs; gluconeogenesis makes glucose during fasting but isn’t the defining state here; lipogenesis builds fat when carbohydrate intake is high.