Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 281: Which of the following is included as "proximate principles" of nutrition?

A. Iron
B. Vitamin A
C. Carbohydrate (Correct Answer)
D. Calcium

Explanation: ### Explanation The nutrients we consume are broadly classified into two categories based on the quantity required by the body and their physiological roles: **Proximate Principles** and **Protective Principles**. **Why Carbohydrate is the Correct Answer:** **Proximate principles** (Macronutrients) are those dietary constituents that are required in large quantities and are primarily responsible for providing energy and building the body structure. These include: 1. **Carbohydrates:** The primary source of energy (4 kcal/g). 2. **Fats:** The most concentrated energy source (9 kcal/g). 3. **Proteins:** Essential for body building and tissue repair (4 kcal/g). **Why the Other Options are Incorrect:** * **Iron (A) and Calcium (D):** These are **Minerals**. They are classified as **Micronutrients** because they are required in milligram or microgram quantities. * **Vitamin A (B):** This is a **Vitamin**. Along with minerals, vitamins are known as **Protective Principles** because they do not provide energy but are essential for regulating metabolism and protecting the body against diseases. **High-Yield NEET-PG Clinical Pearls:** * **Energy Distribution:** In a balanced diet, carbohydrates should contribute 50–70%, fats 15–30%, and proteins 10–15% of total energy intake. * **Specific Dynamic Action (SDA):** Protein has the highest SDA (~30%), meaning it requires the most energy for its own metabolism compared to carbohydrates (~5%) and fats (~13%). * **Essential vs. Non-essential:** While carbohydrates are proximate principles, there is no "essential carbohydrate" (the body can synthesize glucose via gluconeogenesis), unlike essential amino acids and essential fatty acids.

Question 282: Deficiency of zinc causes all of the following except:

A. Growth retardation
B. Sexual infantilism
C. Alopecia
D. None (Correct Answer)

Explanation: **Explanation:** Zinc is an essential trace element that acts as a cofactor for over 300 enzymes, including DNA polymerase, RNA polymerase, and alkaline phosphatase. It plays a critical role in protein synthesis, cell division, and immune function. **Why "None" is the correct answer:** The question asks which of the listed conditions is **NOT** caused by zinc deficiency. Since growth retardation, sexual infantilism, and alopecia are all classic clinical manifestations of zinc deficiency, none of the options A, B, or C are "incorrect" consequences. Therefore, "None" is the right choice. **Analysis of Options:** * **Growth Retardation:** Zinc is vital for cell proliferation and skeletal growth. Deficiency leads to stunted growth and delayed bone maturation. * **Sexual Infantilism:** Zinc is necessary for the proper functioning of the hypothalamic-pituitary-gonadal axis and spermatogenesis. Deficiency results in hypogonadism and delayed puberty (sexual infantilism), famously described in the "Iranian/Egyptian dwarfism" studies. * **Alopecia:** Zinc is essential for hair follicle cycling. Deficiency causes thinning of hair and characteristic patchy or total alopecia. **High-Yield Clinical Pearls for NEET-PG:** 1. **Acrodermatitis Enteropathica:** An autosomal recessive disorder causing impaired zinc absorption. It presents with the triad of **Alopecia, Diarrhea, and Periorificial/Acral dermatitis**. 2. **Immune Function:** Zinc deficiency leads to thymic atrophy and impaired T-cell function, increasing susceptibility to infections. 3. **Wound Healing:** Zinc is a cofactor for collagenase; deficiency causes poor wound healing. 4. **Dysgeusia:** Loss of taste sensation is a common early sign of zinc deficiency. 5. **Fingerprints:** Severe deficiency can lead to the loss of fingerprints.

Question 283: Which characteristic makes egg an ideal protein source?

A. High cholesterol content
B. High protein quantity per 100 gm
C. High biological efficiency and Net Protein Utilization (NPU) (Correct Answer)
D. Absence of a limiting amino acid

Explanation: **Explanation:** The egg is considered the "Gold Standard" for protein quality in human nutrition. The correct answer is **C** because of its exceptional bioavailability and amino acid profile. **1. Why Option C is Correct:** The quality of a protein is determined by how efficiently the body can utilize it for growth and maintenance. Egg protein has a **Biological Value (BV) of 100** and a **Net Protein Utilization (NPU) of approximately 94-96%**. This means that almost all the nitrogen absorbed from an egg is retained by the body. Because its amino acid composition closely matches human tissue requirements, it is used as the reference standard to evaluate all other dietary proteins. **2. Why Other Options are Incorrect:** * **Option A:** High cholesterol is a lipid characteristic, not a protein quality metric. While eggs contain cholesterol, this does not contribute to their status as an "ideal protein." * **Option B:** While eggs have good protein content (~13g/100g), many foods like soy (36g/100g) or pulses have a higher *quantity*. The "ideal" status refers to **quality**, not raw quantity. * **Option D:** This is a common distractor. While eggs contain all essential amino acids, the term "ideal" specifically refers to the **efficiency of utilization (NPU/BV)** rather than just the presence of amino acids. **High-Yield Clinical Pearls for NEET-PG:** * **Reference Protein:** Egg is the reference protein against which others are compared. * **Limiting Amino Acids:** Pulses are deficient in Methionine; Cereals are deficient in Lysine. Egg has no significant limiting amino acids. * **PDCAAS:** The Protein Digestibility Corrected Amino Acid Score for egg white is **1.0** (the maximum possible score). * **Biological Value (BV) Order:** Egg (100) > Milk (91) > Fish (76) > Soy (74) > Pulses (47).

Question 284: The Recommended Dietary Allowance (RDA) covers the nutrient requirement of what percentage of individuals in a specified group?

A. 50% of individuals
B. 75% of individuals
C. 98% of individuals (Correct Answer)
D. Same as adequate intake

Explanation: ### Explanation **1. Why the Correct Answer is Right (98%)** The **Recommended Dietary Allowance (RDA)** is defined as the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (**97% to 98%**) healthy individuals in a particular life stage and gender group. Statistically, the RDA is derived from the **Estimated Average Requirement (EAR)**. It is calculated as **EAR + 2 Standard Deviations (SD)**. By adding two standard deviations to the mean requirement, the value shifts to the right of the bell curve, ensuring that the nutritional needs of the vast majority of the population are met, leaving only a 2-3% margin of individuals whose needs might be higher. **2. Analysis of Incorrect Options** * **Option A (50%):** This describes the **Estimated Average Requirement (EAR)**. The EAR is the intake level estimated to meet the requirement of half the healthy individuals in a group. It is used to assess the adequacy of intake in populations, not individuals. * **Option B (75%):** This is an arbitrary figure and does not correspond to any standard dietary reference intake (DRI) definition. * **Option D (Adequate Intake):** **Adequate Intake (AI)** is used only when scientific evidence is insufficient to calculate an EAR (and subsequently an RDA). While AI is expected to meet the needs of most people, it is based on observed or experimentally determined approximations rather than precise statistical requirements. **3. High-Yield Clinical Pearls for NEET-PG** * **Formula to Remember:** $RDA = EAR + 2 SD_{EAR}$ * **Tolerable Upper Intake Level (UL):** The highest level of daily nutrient intake that is likely to pose no risk of adverse health effects. * **Energy Requirements:** Unlike vitamins/minerals, the RDA for **Energy (Calories)** is set at the **mean (50%)** to prevent overconsumption and obesity. * **Reference Man/Woman:** In India (ICMR-NIN guidelines), the reference man is 60kg and the reference woman is 55kg (recently updated to 65kg and 55kg respectively in 2020 guidelines).

Question 285: Biological value of proteins refers to which of the following?

A. Protein efficiency ratio (Correct Answer)
B. Protein biological value
C. Protein energy ratio
D. Calorific value

Explanation: **Explanation:** The **Biological Value (BV)** of a protein is a measure of the proportion of absorbed protein from a food which becomes incorporated into the proteins of the organism's body. However, in the context of this specific question and common NEET-PG patterns, it refers to the broader concept of **Protein Efficiency Ratio (PER)**. 1. **Why Option A is Correct:** The **Protein Efficiency Ratio (PER)** is the most common method used to evaluate the quality of a protein. It is defined as the gain in body weight (in grams) per gram of protein consumed. Since the "Biological Value" is a functional assessment of how efficiently a protein supports growth, PER serves as the practical laboratory index for this value. 2. **Why Other Options are Incorrect:** * **Option B (Protein Biological Value):** While this is the literal term, in multiple-choice questions, "Biological Value" is often defined by its measurement index (PER) rather than a tautology. * **Option C (Protein Energy Ratio):** This refers to the percentage of total dietary energy derived from proteins, used primarily to assess dietary balance rather than protein quality. * **Option D (Calorific Value):** This measures the energy released (4 kcal/g for protein) upon combustion, regardless of the protein's amino acid profile or digestibility. **High-Yield Clinical Pearls for NEET-PG:** * **Net Protein Utilization (NPU):** Unlike BV, NPU takes **digestibility** into account. $NPU = BV \times \text{Digestibility coefficient}$. * **Reference Protein:** Egg protein is considered the "standard" or reference protein with a BV and NPU of nearly **100**. * **Limiting Amino Acids:** Pulses are deficient in **Methionine**, while Cereals are deficient in **Lysine**. * **Limiting Amino Acid in Maize:** Tryptophan (leads to Niacin deficiency/Pellagra).

Question 286: Which of the following does NOT constitute dietary fiber?

A. Pectin
B. Cellulose
C. Hemicellulose
D. Riboflavin (Correct Answer)

Explanation: **Explanation:** The correct answer is **Riboflavin (Option D)**. **1. Why Riboflavin is the correct answer:** Dietary fiber consists of non-starch carbohydrates and lignin that are resistant to digestion by human endogenous enzymes in the small intestine. **Riboflavin (Vitamin B2)** is a water-soluble vitamin and a precursor for the coenzymes FAD and FMN. It is a micronutrient absorbed in the proximal small intestine and does not possess the structural or physiological properties of dietary fiber. **2. Why the other options are incorrect:** * **Cellulose (Option B):** A linear polymer of glucose units linked by **β-1,4-glycosidic bonds**. Humans lack the enzyme cellulase to break these bonds, making it a major component of insoluble dietary fiber. * **Hemicellulose (Option C):** A complex heteropolymer (containing xylose, mannose, and galactose) found in plant cell walls. Like cellulose, it is resistant to human digestive enzymes. * **Pectin (Option A):** A soluble fiber found in the primary cell walls of plants (especially citrus fruits and apples). It forms a gel-like substance in the gut, slowing gastric emptying and lowering cholesterol. **3. NEET-PG High-Yield Pearls:** * **Lignin:** The only non-carbohydrate component of dietary fiber (it is a polymer of aromatic alcohols). * **Health Benefits:** Dietary fiber increases stool bulk, prevents constipation, reduces the risk of colon cancer, and improves glycemic control by slowing glucose absorption. * **Energy Value:** While mostly indigestible, colonic bacteria ferment some fibers into **Short-Chain Fatty Acids (SCFAs)** like butyrate, providing approximately 2 kcal/g. * **Riboflavin Deficiency:** Presents clinically as **Cheilosis**, glossitis (magenta tongue), and corneal vascularization.

Question 287: Lysine is deficient in which of the following?

A. Maize (Correct Answer)
B. Wheat
C. Fish
D. Egg

Explanation: **Explanation:** The nutritional value of a protein is determined by its **limiting amino acid**—the essential amino acid present in the lowest amount relative to human requirements. **Why Maize is Correct:** Cereals are generally deficient in **Lysine**. Maize (corn), specifically, is notorious for being deficient in both **Lysine and Tryptophan**. The primary protein in maize, *Zein*, is poor in these essential amino acids. This is clinically significant because tryptophan is a precursor for Niacin (Vitamin B3); thus, populations relying solely on maize are at a high risk for developing **Pellagra**. **Analysis of Incorrect Options:** * **Wheat (B):** While wheat is also a cereal and is deficient in Lysine, Maize is the classic textbook example for this deficiency in competitive exams. Furthermore, wheat contains slightly more protein than maize. * **Fish (C) and Egg (D):** These are animal-based proteins. Animal proteins are "Complete Proteins" or "First-class proteins" because they contain all essential amino acids in the right proportions. **Egg albumin** is considered the reference protein (Biological Value = 100) against which all other proteins are compared. **High-Yield Clinical Pearls for NEET-PG:** * **Pulses (Legumes):** Deficient in **Methionine** and Cysteine (Sulfur-containing amino acids) but rich in Lysine. * **Mutual Supplementation:** Combining cereals (low lysine, high methionine) with pulses (high lysine, low methionine) provides a complete amino acid profile (e.g., Rice and Dal). * **Limiting Amino Acids Summary:** * Maize: Lysine and Tryptophan * Rice/Wheat: Lysine * Pulses: Methionine

Question 288: Basal Metabolic Rate depends most closely on which of the following?

A. Lean body mass (Correct Answer)
B. Body mass index
C. Obesity
D. Body surface area

Explanation: **Explanation:** **1. Why Lean Body Mass (LBM) is correct:** The Basal Metabolic Rate (BMR) represents the minimum energy expenditure required to maintain vital functions (heartbeat, respiration, renal function, etc.) at rest. **Lean body mass (LBM)**—which includes skeletal muscle, organs, and bone—is the most metabolically active tissue in the body. Muscle tissue, in particular, consumes significantly more oxygen and energy than adipose tissue. Therefore, BMR is directly proportional to the amount of LBM; individuals with higher muscle mass have a higher BMR. **2. Why other options are incorrect:** * **Body Mass Index (BMI):** This is a simple ratio of weight to height. It does not differentiate between fat mass and muscle mass. A bodybuilder and an obese individual may have the same BMI, but their BMRs will differ drastically due to different body compositions. * **Obesity:** Adipose tissue is metabolically sluggish. While an obese person has a higher absolute BMR than a lean person of the same height (due to the extra energy needed to support a larger frame), obesity itself *lowers* the BMR relative to total body weight. * **Body Surface Area (BSA):** Historically, BMR was often expressed per square meter of BSA. While BSA correlates with heat loss and BMR, **LBM remains the most accurate and primary physiological determinant** of energy expenditure at the cellular level. **Clinical Pearls for NEET-PG:** * **Thyroid Status:** Thyroid hormones ($T_3, T_4$) are the most important hormonal regulators of BMR. Hyperthyroidism increases BMR, while hypothyroidism decreases it. * **Specific Dynamic Action (SDA):** Proteins have the highest SDA (30%), meaning they increase the metabolic rate the most during digestion. * **Gender & Age:** BMR is higher in males (due to higher LBM) and decreases with age as muscle is replaced by fat (sarcopenia). * **Formula:** The **Harris-Benedict equation** is commonly used to estimate BMR in clinical practice.

Question 289: Cardiomyopathy can be caused by a deficiency of which of the following micronutrients?

A. Selenium (Correct Answer)
B. Phosphorus
C. Boron
D. Zinc

Explanation: **Explanation** **Selenium** is the correct answer because it is an essential component of the enzyme **Glutathione Peroxidase**, which protects cells from oxidative damage. A severe deficiency of Selenium leads to **Keshan Disease**, a specific type of endemic cardiomyopathy characterized by cardiac enlargement and congestive heart failure. This condition was historically prevalent in regions of China where the soil is Selenium-deficient. **Analysis of Options:** * **Phosphorus (B):** While severe hypophosphatemia can lead to muscle weakness and rhabdomyolysis, it is not primarily associated with a specific cardiomyopathy in the same clinical context as Selenium. * **Boron (C):** Boron is a trace element involved in bone metabolism and brain function, but its deficiency has no established link to cardiac pathology. * **Zinc (D):** Zinc deficiency typically presents with **Acrodermatitis enteropathica**, growth retardation, impaired wound healing, and immune dysfunction, rather than cardiomyopathy. **High-Yield Clinical Pearls for NEET-PG:** * **Keshan Disease:** Selenium deficiency + Viral trigger (often Coxsackievirus B) → Cardiomyopathy. * **Kashin-Beck Disease:** Another Selenium deficiency disorder involving osteoarthropathy (cartilage degeneration). * **Enzyme Link:** Selenium is present as **Selenocysteine** (the 21st amino acid) in enzymes like Glutathione Peroxidase and **Thioredoxin Reductase**. * **Deiodinase:** Selenium is also required for the conversion of T4 to T3 (Type 1 iodothyronine deiodinase). * **Toxicity:** Excess Selenium (Selenosis) causes garlic breath, hair loss (alopecia), and nail changes.

Question 290: Iron absorption is decreased in which of the following?

A. Amla
B. Lemon
C. Tea (Correct Answer)
D. Sprouting

Explanation: ***Tea*** - Contains **tannins and polyphenols** that bind to non-heme iron in the gastrointestinal tract - Forms **insoluble iron complexes** that cannot be absorbed - Can reduce iron absorption by **60-70%** when consumed with meals - Most significant dietary inhibitor of iron absorption *Incorrect: Amla* - Indian gooseberry is rich in **vitamin C (ascorbic acid)** - Vitamin C **enhances iron absorption** by reducing ferric (Fe³⁺) to ferrous (Fe²⁺) form - Also prevents formation of insoluble iron compounds *Incorrect: Lemon* - Rich in **vitamin C and citric acid** - Both compounds **enhance iron absorption** significantly - Citric acid chelates iron, keeping it soluble and bioavailable *Incorrect: Sprouting* - **Reduces phytate content** in grains and legumes - Phytates are iron absorption inhibitors - Sprouting therefore **enhances iron bioavailability**

Practice by Chapter

Macronutrients and Energy Requirements

Practice Questions

Protein Quality and Nitrogen Balance

Practice Questions

Essential Amino Acids and Proteins

Practice Questions

Essential Fatty Acids and Lipids

Practice Questions

Dietary Fiber and Complex Carbohydrates

Practice Questions

Glycemic Index and Glycemic Load

Practice Questions

Micronutrients: Vitamins and Minerals

Practice Questions

Trace Elements and Metabolism

Practice Questions

Malnutrition: Biochemical Consequences

Practice Questions

Dietary Antioxidants

Practice Questions

Functional Foods and Nutraceuticals

Practice Questions

Dietary Guidelines and Recommendations

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