Question

Maximum energy per gram on oxidation is yielded from

• A. Starch
• B. Fat
• C. Glycogen
• D. Protein

Hint:

Fats provide more energy per gram than carbohydrates or proteins due to their higher carbon-hydrogen content.

Answer 1

The Correct Option is B

Energy released on oxidation depends on how reduced a fuel molecule is -- more C-H bonds and fewer oxygen-bearing groups mean more energy released per gram.

Starch and glycogen are both glucose polymers with the same partially oxidized carbon backbone, and protein's energy yield is limited by its nitrogen content, which must be removed before the remaining carbon skeleton is oxidized.

Fat's long hydrocarbon chains are far more reduced than any of these, so it yields the most energy per gram on oxidation.

Answer 2

Comparing the approximate energy values per gram for each macronutrient class settles this directly.

1. Starch: As a carbohydrate, it yields roughly 4 kilocalories per gram on complete oxidation.
2. Fat: Fat yields roughly 9 kilocalories per gram, more than double the value for carbohydrate or protein, because of its highly reduced hydrocarbon structure.
3. Glycogen: Also a carbohydrate polymer, yielding around 4 kilocalories per gram, the same range as starch.
4. Protein: Yields roughly 4 kilocalories per gram as well, similar to carbohydrates, since its energy contribution is limited by its partially oxidized and nitrogen-containing structure.

Only fat's per-gram caloric value stands well above the other three options.

So, the correct answer is fat.