Which of the following constituents of food is the chief source of energy?

RRB Staff Nurse Jaipur-6th June 2018

Applied Nutrition & Dietetics

Easy

Appeared in: RRB Staff Nurse Jaipur-6th June 2018

Explanation

Carbohydrates are the body's main and most efficient source of fuel, providing 4 kcal of energy per gram.
They are readily broken down into glucose, which is the preferred energy currency for all cells, and the primary fuel for the brain and central nervous system.
Dietary guidelines recommend that carbohydrates make up the largest portion of daily caloric intake (typically 45-65%) to meet the body's immediate energy demands.

Option B: The primary role of proteins is to serve as building blocks for body tissues, enzymes, and hormones, not to be the main energy source.
Option C: Vitamins are micronutrients that are essential for metabolism but do not provide any calories or energy.
Option D: Although lipids (fats) are the most energy-dense nutrient (9 kcal/g), they function as a long-term energy reserve, not the body's primary or 'chief' source for immediate daily activities.

Visual 1: Infographic: A food pyramid or 'My Plate' diagram showing the recommended proportions of macronutrients, with carbohydrates (grains, fruits, vegetables) forming a significant portion.
Visual 2: Flowchart: A simple diagram illustrating metabolic pathways: Carbohydrates -> Glucose -> ATP (Energy), highlighting its directness compared to the more complex pathways for converting protein and fat to energy.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Macronutrients as Energy Sources as background academic context rather than a clinical decision trigger.
In clinical practice, ensuring adequate carbohydrate intake is vital for patient recovery. It has a 'protein-sparing' effect, preventing the breakdown of muscle tissue for energy so that protein can be used for healing and immune function.
For patients with diabetes, monitoring the amount and type (simple vs. complex) of carbohydrates is fundamental to managing blood glucose levels and preventing complications.
What if? If a patient is made 'Nothing by Mouth' (NPO) for surgery, their body uses stored glycogen (from carbohydrates) first. If NPO status is prolonged without IV dextrose, the body shifts to breaking down fat and then muscle for energy, leading to ketosis and muscle wasting, which can delay recovery.

How to Approach the Question

Identify the keyword in the question: 'chief source'. This asks for the primary or main source of energy, not necessarily the most concentrated.
Recall the primary functions of the four listed food constituents.
Compare the roles: Carbohydrates are for immediate energy, Proteins are for building/repair, Lipids are for stored energy, and Vitamins are for regulation.
Differentiate between 'energy-dense' (Lipids at 9 kcal/g) and 'chief source' (Carbohydrates, which the body prefers to use first).
Conclude that carbohydrates are the 'chief' source because they are the body's most readily available and preferred fuel for daily functions.

Concept Tested & Keywords

q3Uh8GbJz-gmX7pzyr9MR