Macronutrient Science Fundamentals Flashcards

Dietary fiber is classified as a carbohydrate but provides only approximately 2 kcal/gram (vs. 4 kcal/gram for digestible carbohydrates). This is because:

Answer: Fiber is largely indigestible by human digestive enzymes and passes to the colon, where it is fermented by gut bacteria

Humans lack the enzymes to digest most dietary fiber. It passes intact to the colon, where gut bacteria ferment it — producing short-chain fatty acids (SCFAs) and providing roughly 2 kcal/gram.

Which of the following is NOT an essential fatty acid that humans must obtain from diet?

Answer: Oleic acid (omega-9)

Oleic acid (omega-9) is not essential because the body can synthesize it endogenously through desaturation of stearic acid. ALA (omega-3) and LA (omega-6) cannot be synthesized and must come from food.

During a prolonged fast or severe carbohydrate restriction, the brain adapts to using which alternative fuel source?

Answer: Ketone bodies (produced by the liver from fatty acids)

After 3–4 days of carbohydrate restriction or fasting, the liver produces ketone bodies (beta-hydroxybutyrate, acetoacetate, acetone) from fatty acids, which the brain can use as an alternative to glucose.

Protein turnover refers to the balance between which two processes?

Answer: Muscle protein synthesis (MPS) and muscle protein breakdown (MPB)

Protein turnover is the continuous cycle of muscle protein synthesis (building new proteins) and muscle protein breakdown (degrading existing proteins). Net muscle gain occurs when MPS > MPB.

The glycemic index (GI) measures:

Answer: How rapidly a food raises blood glucose relative to pure glucose (or white bread)

GI ranks carbohydrate-containing foods on a scale of 0–100 based on how quickly they raise blood glucose compared to pure glucose (GI=100), reflecting the rate of carbohydrate digestion and absorption.

Negative nitrogen balance occurs when:

Answer: Nitrogen excretion exceeds nitrogen intake, indicating net protein (muscle) breakdown

Nitrogen balance measures protein status. Negative nitrogen balance (more nitrogen excreted than consumed) indicates net protein catabolism — the body is breaking down more muscle than it builds.