With aging, which combination best describes changes in substrate utilization?

With aging, which combination best describes changes in substrate utilization?

• A. Decreased glucose oxidation and increased free fatty acids
• B. Increased glucose oxidation and increased free fatty acids
• C. Decreased glucose oxidation and decreased free fatty acids
• D. Increased glucose oxidation and decreased free fatty acids

Answer: (A)

Aging commonly shifts the body toward using fat rather than carbohydrate for energy. Insulin sensitivity tends to decline with age, reducing glucose uptake and oxidation, while lipolysis in adipose tissue can increase, raising circulating free fatty acids. This combination—less glucose oxidation and more free fatty acids available for oxidation—best describes the pattern seen in older adults. The other patterns would require more glucose oxidation or less fatty acid availability, which are not characteristic of typical aging metabolism.

Aging commonly shifts the body toward using fat rather than carbohydrate for energy. Insulin sensitivity tends to decline with age, reducing glucose uptake and oxidation, while lipolysis in adipose tissue can increase, raising circulating free fatty acids. This combination—less glucose oxidation and more free fatty acids available for oxidation—best describes the pattern seen in older adults. The other patterns would require more glucose oxidation or less fatty acid availability, which are not characteristic of typical aging metabolism.