The food substance that would produce the highest amount of energy is

Step 1: Analyze the question The question asks which food substance releases the most energy per unit mass when it is broken down (oxidized) in the body.

Step 2: Explain the concept The energy values of the main food classes are:

| Food substance | Energy per gram | |---|---| | Fat (lipid) | about 37-39 kJ (about 9 kcal) | | Carbohydrate (e.g. glucose) | about 17 kJ (about 4 kcal) | | Protein | about 17 kJ (about 4 kcal) |

Fats have the highest energy value because their molecules contain many carbon-hydrogen bonds and relatively little oxygen. More carbon-hydrogen bonds means more oxidation is possible, so more energy is released. This is why fat is the body's main long-term energy store.

Step 3: Apply to the options

• A. Protein: about 17 kJ/g. It is mainly for growth and repair, and is only used for energy as a last resort.
• B. Amino acid: the building block of protein, with a similar or lower energy value. It is not an energy-rich food class.
• C. Fat: about 39 kJ/g, which is more than double the others.
• D. Glucose: about 15-17 kJ/g. It is the quickest source of energy, but not the highest in amount.

Step 4: Answer Fat gives the highest energy per gram, so the correct option is C.

Tip: Remember the "9-4-4" rule: fat gives 9 kcal/g, while carbohydrate and protein give 4 kcal/g each. If a WASSCE, JAMB or NECO question asks for the highest energy, think "fat". If it asks for the quickest energy, think "glucose/carbohydrate".