Question

How much metabolic water (% of weight) is produced from metabolism of protein?

• A. 20
• B. 40
• C. 60
• D. 80

Hint:

Metabolic water yields follow this order: Fats (\(107\%\)) $>$ Carbohydrates (\(60\%\)) $>$ Proteins (\(40\%\)). Fats produce more than double the metabolic water of proteins per gram.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Metabolic water refers to the water produced internally inside an organism through the biochemical oxidation of dietary macronutrients (carbohydrates, fats, and proteins) during cellular respiration.
The yield of metabolic water varies among different classes of nutrients because of their distinct chemical structures and hydrogen-to-oxygen ratios.

Step 2: Detailed Explanation:
When macronutrients are oxidized inside the cells, hydrogen atoms combine with oxygen to form water molecules as a final product of the electron transport chain.
The stoichiometric yields of metabolic water per 100 grams of metabolized nutrient are as follows:
Fats: Yield approximately 107 to 110 grams of water (about \(107\%\) of their weight), because they are highly reduced hydrocarbons with a high proportion of hydrogen atoms.
Carbohydrates (Starch/Glucose): Yield approximately 55 to 60 grams of water (about \(60\%\) of their weight).
Proteins: Yield approximately 40 to 42 grams of water (about \(40\%\) of their weight).
The water yield for protein is lower because protein metabolism is incomplete; the nitrogenous amino groups are excreted as urea or uric acid, which carries away some of the hydrogen atoms.
Therefore, the amount of metabolic water produced from protein metabolism is approximately \(40\%\) of its metabolized weight.

Step 3: Final Answer:
Metabolic water produced from the metabolism of protein is approximately 40% of its weight.