Which of the following statements correctly describes a key difference between proteins and the energy nutrients carbohydrates and fats in the human body?

Introduction / Context:
The human body uses carbohydrates, fats, and proteins in different ways. This question tests whether you know how these nutrients are handled, especially regarding storage. Understanding this difference is important in nutrition, metabolism, and health science topics such as obesity and malnutrition.

Given Data / Assumptions:

• The question compares proteins with carbohydrates and fats.
• We are looking for a statement that highlights a correct and important difference.
• We assume basic knowledge of macromolecules and nutrient storage.

Concept / Approach:
Carbohydrates and fats are primarily energy sources. When consumed in excess, carbohydrates can be stored as glycogen and later converted to fat, while fats are stored in adipose tissue. Proteins are mainly used for growth, repair, and maintenance of body tissues. The body has very limited capacity to store extra protein. Excess amino acids are deaminated, and their carbon skeletons may be used for energy or converted to fat, while the nitrogen is excreted as urea. Therefore, excess protein is not stored as protein reserves in a dedicated tissue.

Step-by-Step Solution:
Step 1: Examine how carbohydrates are stored. They are stored as glycogen in liver and muscles, and long term excess is converted to fat. Step 2: Examine how fats are stored. Fats are easily stored in adipose tissue as a long term energy reserve. Step 3: Examine how proteins are handled. The body uses proteins for structure, enzymes, and hormones. Excess amino acids are broken down rather than stored as protein. Step 4: Identify the option that states this correct difference. Option B fits perfectly by stating that excess carbohydrates and fats are stored, whereas excess proteins are not stored in the same way.

Verification / Alternative check:
Nutrition and physiology textbooks explain that there is no large protein storage depot equivalent to fat stores or glycogen stores. Muscle proteins are functional, not spare storage that the body wants to use. Breaking down muscle for energy happens mainly in starvation. This confirms that excess protein is not stored in a dedicated form, while carbohydrates and fats are.

Why Other Options Are Wrong:

• Option A: Carbohydrates are also made of monomers (monosaccharides) and fats are built from units such as fatty acids and glycerol, so the statement is false.
• Option C: Carbohydrates, fats, and proteins are all macromolecules in biological systems.
• Option D: Proteins also contain carbon, hydrogen, and oxygen, and in addition they contain nitrogen, so the statement is incorrect.

Common Pitfalls:
Students sometimes believe all nutrients are stored in similar ways. Remember that carbohydrates and fats play a major role as energy reserves, while protein is mainly functional. Another common confusion is thinking that muscle is simply a protein store. In reality, muscle tissue has active roles and is not meant to be a storage depot under normal conditions.

Final Answer:
The correct difference is that excess carbohydrates and fats are stored, whereas excess proteins are generally not stored in the same way.