Question

.......... serve as a fuel molecule in foods

• A. Proteins
• B. Minerals
• C. Vitamins
• D. Lipids

Hint:

Lipids = high-energy fuel molecules; key energy source in foods.

Answer 1

The Correct Option is D

Fuel Molecules

A fuel molecule is a substance that contains stored chemical energy that can be readily released and converted into a usable form of energy, often for the purpose of powering processes or generating heat. Fuel molecules are the molecules that living cells metabolize to generate adenosine triphosphate (ATP), which is the primary energy currency of the cell. They can also generate other activated carrier molecules like NADPH.

Let's examine each option:

Proteins

Proteins are primarily structural and functional molecules, though they can serve as fuel in certain circumstances.

• Main function: Building and repairing tissues, enzymes, hormones
• Provide 4 kcal/gram when used for energy
• Not the body's preferred energy source (used only during starvation or excessive intake)

Minerals

Minerals are inorganic elements that serve various regulatory and structural roles.

• Function as cofactors for enzymes (e.g., iron in hemoglobin)
• Maintain electrolyte balance and bone structure
• Contain zero calories - cannot serve as fuel

Vitamins

Vitamins are organic micronutrients that assist in metabolic processes.

• Function as coenzymes in energy metabolism
• Help release energy from macronutrients but don't provide energy themselves
• Contain zero calories - cannot serve as fuel

Lipids

Lipids (fats) are one of the three primary macronutrients that serve as major fuel molecules.

• Provide 9 kcal/gram (most energy-dense nutrient)
• Stored in adipose tissue as long-term energy reserve
• Primary fuel during rest and low-intensity exercise
• Essential for absorption of fat-soluble vitamins

Additional Note on Carbohydrates

While not listed in the options, carbohydrates are the other primary fuel molecule:

• Provide 4 kcal/gram
• Preferred energy source for brain and high-intensity exercise
• Stored as glycogen in liver and muscles

Why Lipids Are the Best Answer

Among the given options, lipids are the most correct answer because:

1. They are specifically evolved as the body's main long-term energy storage molecules
2. Provide more than twice the energy per gram compared to proteins or carbohydrates
3. The body maintains specialized fat cells (adipocytes) specifically for fuel storage

Metabolic Pathways Comparison

Nutrient	Fuel Role	Energy Density	Storage Form
Lipids	Primary long-term fuel	9 kcal/g	Triglycerides in adipose tissue
Proteins	Emergency fuel only	4 kcal/g	No dedicated storage
Minerals/Vitamins	No fuel value	0 kcal	N/A

Final Answer

The nutrient that serves as a primary fuel molecule in foods is Lipids.