During fasting, which statement about leucine is correct?

During fasting, which statement about leucine is correct?

• A. Leucine oxidation decreases to spare glucose
• B. Leucine oxidation increases; acetyl-CoA produced; pyruvate spared from oxidation
• C. Leucine is converted to glucose in muscle to supply energy
• D. Leucine inhibits hepatic gluconeogenesis

Answer: (B)

During fasting, amino acid metabolism shifts to provide energy, and leucine behaves as a strictly ketogenic amino acid. That means its carbon skeleton is converted to acetyl-CoA (and ketone bodies), not to glucose. As fasting continues, leucine oxidation increases to supply acetyl-CoA for the TCA cycle and for ketogenesis, rather than forming pyruvate for gluconeogenesis. Because leucine cannot be converted into pyruvate or glucose, its oxidation does not consume pyruvate; this helps keep pyruvate available for other metabolic needs. Putting these points together, the description that leucine oxidation increases, acetyl-CoA is produced, and pyruvate is spared from oxidation correctly reflects leucine’s fate during fasting. Leucine is not used to make glucose in muscle, and it does not inhibit hepatic gluconeogenesis.

During fasting, amino acid metabolism shifts to provide energy, and leucine behaves as a strictly ketogenic amino acid. That means its carbon skeleton is converted to acetyl-CoA (and ketone bodies), not to glucose. As fasting continues, leucine oxidation increases to supply acetyl-CoA for the TCA cycle and for ketogenesis, rather than forming pyruvate for gluconeogenesis. Because leucine cannot be converted into pyruvate or glucose, its oxidation does not consume pyruvate; this helps keep pyruvate available for other metabolic needs. Putting these points together, the description that leucine oxidation increases, acetyl-CoA is produced, and pyruvate is spared from oxidation correctly reflects leucine’s fate during fasting. Leucine is not used to make glucose in muscle, and it does not inhibit hepatic gluconeogenesis.