Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 61: In Oral Rehydration Solution (ORS), what is the effect of glucose on sodium absorption?

A. Increase in sodium absorption (Correct Answer)
B. Decrease in sodium absorption
C. Variable effect on sodium absorption
D. No effect on sodium absorption

Explanation: ### Explanation **1. Why Option A is Correct:** The core mechanism of Oral Rehydration Solution (ORS) relies on the **SGLT-1 (Sodium-Glucose Linked Transporter 1)** protein located in the brush border of the small intestinal enterocytes. This transporter facilitates the **symport** (coupled transport) of one molecule of glucose with two ions of sodium. Even in cases of severe secretory diarrhea (like Cholera), where cAMP-mediated chloride secretion is high, the SGLT-1 transporter remains functional. When glucose is present in the intestinal lumen, it "drags" sodium along with it into the cell. This increase in intracellular osmolarity subsequently promotes the passive absorption of water via the osmotic gradient. Therefore, glucose is added to ORS not for calories, but specifically to **increase sodium and water absorption.** **2. Why Other Options are Incorrect:** * **Option B & D:** Glucose does not inhibit or ignore sodium; it is the primary physiological driver for sodium uptake in the post-prandial state and during rehydration therapy. * **Option C:** The effect is not variable; it is a consistent, stoichiometric relationship (2 Na⁺ : 1 Glucose) that forms the physiological basis of WHO-recommended ORS formulations. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Standard vs. Reduced Osmolarity ORS:** The current WHO recommendation is **Reduced Osmolarity ORS (245 mOsm/L)**, which reduces the risk of unscheduled IV fluids and stool output compared to the older version (311 mOsm/L). * **Composition of Reduced ORS:** * Sodium: 75 mmol/L * Glucose: 75 mmol/L (Note the 1:1 molar ratio for optimal absorption) * Potassium: 20 mmol/L * Chloride: 65 mmol/L * Citrate: 10 mmol/L * **Trisodium Citrate:** Added to ORS to correct metabolic acidosis resulting from diarrhea. * **Zinc Supplementation:** Often given alongside ORS (20 mg/day for 10-14 days) to reduce the duration and severity of diarrhea episodes.

Question 62: Which of the following is an indicator of moderate to severe malnutrition?

A. Serum transferrin 160 mg/dL
B. Body mass index 19 kg/m
C. Albumin 2.1 g/dL (Correct Answer)
D. Transthyretin

Explanation: **Explanation:** The assessment of nutritional status relies on anthropometric measurements and biochemical markers (visceral proteins). **1. Why Albumin 2.1 g/dL is correct:** Serum albumin is the most commonly used laboratory marker for chronic malnutrition. While it has a long half-life (~20 days) and is an "acute-phase reactant" (levels drop during inflammation), it remains a key indicator of protein-energy status. * **Normal range:** 3.5–5.0 g/dL * **Mild malnutrition:** 2.8–3.4 g/dL * **Moderate to Severe malnutrition:** **< 2.8 g/dL** An albumin level of 2.1 g/dL signifies a significant deficit in visceral protein stores, correlating with moderate to severe malnutrition. **2. Analysis of Incorrect Options:** * **Serum transferrin 160 mg/dL:** Transferrin (half-life ~8 days) is more sensitive than albumin. However, the normal range is 200–400 mg/dL. While 160 mg/dL indicates mild depletion, 2.1 g/dL of albumin represents a more severe clinical state. * **BMI 19 kg/m²:** According to WHO and Asian-specific criteria, a BMI of 18.5–24.9 kg/m² is considered **normal**. Malnutrition (underweight) is defined as BMI < 18.5 kg/m². * **Transthyretin (Pre-albumin):** While this is the **most sensitive** marker for acute changes in nutritional status due to its short half-life (~2 days), the option provides only the name of the marker without a value, making it an incomplete choice compared to the specific pathological value provided for albumin. **Clinical Pearls for NEET-PG:** * **Most sensitive marker for acute malnutrition:** Pre-albumin (Transthyretin). * **Marker with the shortest half-life:** Retinol-binding protein (12 hours). * **Gold standard for body composition:** DEXA scan. * **Kwashiorkor vs. Marasmus:** Low albumin is the hallmark of Kwashiorkor (edematous malnutrition), whereas Marasmus is characterized by severe calorie deficiency and muscle wasting with relatively preserved albumin initially.

Question 63: Which protein is present in brown adipose tissue?

A. Thermogenin (Correct Answer)
B. Dinitroprotein
C. Leptin
D. Adipocin

Explanation: **Explanation:** **Thermogenin (Option A)**, also known as **Uncoupling Protein 1 (UCP1)**, is the correct answer. It is a specialized protein located in the inner mitochondrial membrane of **brown adipose tissue (BAT)**. Its primary function is to act as a proton channel that allows protons ($H^+$) to leak from the intermembrane space back into the mitochondrial matrix, bypassing ATP synthase. This "uncouples" the electron transport chain from ATP synthesis, dissipating the electrochemical gradient as **heat** instead of chemical energy. This process, known as **non-shivering thermogenesis**, is vital for neonates to maintain body temperature. **Analysis of Incorrect Options:** * **Dinitroprotein (Option B):** This is a distractor. However, **2,4-Dinitrophenol (DNP)** is a well-known chemical uncoupler that acts similarly to thermogenin but is exogenous and toxic. * **Leptin (Option C):** A hormone produced primarily by white adipose tissue that regulates energy balance by inhibiting hunger (satiety signal) via the hypothalamus. * **Adipocin (Option D):** Likely a distractor referring to **Adipokines**, which are a general class of cell-signaling proteins (cytokines) secreted by adipose tissue (e.g., adiponectin, resistin). **High-Yield Clinical Pearls for NEET-PG:** * **Brown vs. White Fat:** Brown fat has more mitochondria and high vascularity (giving it the brown color) compared to white fat, which stores energy as triglycerides. * **Mechanism:** Thermogenin is activated by **fatty acids** and inhibited by purine nucleotides (GDP/ADP). * **Sympathetic Control:** Non-shivering thermogenesis is triggered by **Norepinephrine**, which acts on $\beta_3$-adrenergic receptors to stimulate lipolysis and activate UCP1. * **Location:** In adults, brown fat is found in the cervical, supraclavicular, and paravertebral regions.

Question 64: Which of the following vitamins is egg a poor source of?

A. Vitamin A
B. Vitamin B12
C. Vitamin C (Correct Answer)
D. Vitamin E

Explanation: **Explanation:** The correct answer is **Vitamin C**. Eggs are often described as "nature’s multivitamin" because they contain almost every essential vitamin and mineral required by the human body, with one notable exception: **Vitamin C (Ascorbic Acid).** 1. **Why Vitamin C is the correct answer:** Vitamin C is primarily found in plant-based sources, particularly citrus fruits and leafy vegetables. Animal products, including eggs and milk, are notoriously poor sources of Vitamin C. In the context of an egg, the nutrient profile is designed to support the development of a chick embryo; while it provides high-quality proteins, fats, and fat-soluble vitamins, it lacks ascorbic acid entirely. 2. **Analysis of Incorrect Options:** * **Vitamin A:** Eggs are an excellent source of Vitamin A (retinol) and carotenoids (lutein and zeaxanthin), which are concentrated in the egg yolk. * **Vitamin B12:** As an animal-derived product, eggs are a reliable source of Cobalamin (B12), which is essential for DNA synthesis and RBC formation. * **Vitamin E:** The egg yolk contains significant amounts of Vitamin E (tocopherol), acting as a lipid-soluble antioxidant to protect the fatty acids within the yolk. **NEET-PG High-Yield Pearls:** * **The "Rule of Two":** Eggs are a poor source of **Vitamin C** and **Calcium** (the calcium is in the shell, not the edible portion). * **Reference Protein:** Egg protein (albumin) has a **Biological Value (BV) of 100**, making it the gold standard for comparing the quality of other dietary proteins. * **Avidin-Biotin Interaction:** Raw egg whites contain **avidin**, which binds to **biotin (B7)** and prevents its absorption, potentially leading to deficiency if consumed in large quantities over time. Cooking denatures avidin, making the biotin available.

Question 65: All of the following functions require zinc as a micro-element, EXCEPT?

A. Spermatogenesis
B. Fetal growth
C. Embryonic development
D. Melanin synthesis (Correct Answer)

Explanation: **Explanation:** Zinc is a vital trace element that acts as a cofactor for over 300 enzymes (Zinc-metalloproteins) and is essential for structural integrity via "zinc finger motifs" in transcription factors. **Why Melanin Synthesis is the Correct Answer:** Melanin synthesis is primarily dependent on the enzyme **Tyrosinase**, which is a **Copper-containing enzyme**, not zinc-dependent. Tyrosinase catalyzes the rate-limiting step of converting Tyrosine to DOPA and subsequently to dopaquinone. Therefore, copper deficiency, rather than zinc deficiency, leads to hypopigmentation. **Analysis of Incorrect Options:** * **Spermatogenesis:** Zinc is highly concentrated in the testes and prostate. It is essential for DNA synthesis, cell division, and the maintenance of the germinal epithelium. Deficiency leads to oligospermia and testicular atrophy. * **Fetal Growth & Embryonic Development:** Zinc is a constituent of RNA and DNA polymerases. It plays a critical role in rapid cell proliferation and gene expression during embryogenesis. Maternal zinc deficiency is strongly linked to congenital malformations (neural tube defects) and intrauterine growth restriction (IUGR). **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder of zinc absorption characterized by periorificial dermatitis, alopecia, and diarrhea. * **Wound Healing:** Zinc is essential for collagen synthesis and fibroblast proliferation; deficiency causes delayed wound healing. * **Gustin:** A zinc-containing protein in saliva required for taste bud development (deficiency causes **hypogeusia**). * **Carbonic Anhydrase & Alcohol Dehydrogenase:** These are classic examples of zinc-dependent enzymes frequently tested in exams.

Question 66: What is the Net Protein Utilization (NPU) of an egg?

A. 90
B. 96 (Correct Answer)
C. 6
D. 12

Explanation: **Explanation:** **Net Protein Utilization (NPU)** is a key indicator of dietary protein quality. It represents the proportion of ingested nitrogen that is actually retained by the body for maintenance and growth. It is calculated as: *NPU = (Retained Nitrogen / Intake Nitrogen) × 100* or *NPU = Biological Value (BV) × Digestibility Coefficient.* **Why Option B is Correct:** The whole egg is considered the **"Reference Protein"** in nutrition because it contains all essential amino acids in the ideal proportions required by humans. It has the highest NPU among all natural foods, valued at **96**. This indicates that 96% of the nitrogen from egg protein is utilized by the body, reflecting both its high digestibility and superior amino acid profile. **Analysis of Incorrect Options:** * **Option A (90):** This is the NPU for human milk. While human milk is the gold standard for infants, its NPU is slightly lower than that of a whole egg. * **Option C (6) & D (12):** These values are numerically too low for protein quality indices. For context, the **Nitrogen content** of proteins is roughly 16% (used in the Kjeldahl method), and the **Protein Efficiency Ratio (PER)** of an egg is approximately 4.5. **High-Yield Clinical Pearls for NEET-PG:** * **Biological Value (BV):** For an egg, the BV is **100** (the highest). NPU is always slightly lower than BV because NPU accounts for digestibility. * **Limiting Amino Acids:** Eggs have no limiting amino acids. In contrast, Pulses are deficient in **Methionine**, and Cereals are deficient in **Lysine**. * **Reference Standard:** Because of its NPU of 96 and BV of 100, the egg is the benchmark against which all other dietary proteins are compared.

Question 67: Which of the following is the important reactive group of glutathione in its role as an antioxidant?

A. Serine
B. Sulphydryl (Correct Answer)
C. Tyrosine
D. Acetyl-CoA

Explanation: **Explanation:** **Glutathione (GSH)** is a tripeptide composed of three amino acids: **Glutamate, Cysteine, and Glycine**. It serves as the body’s premier endogenous antioxidant, protecting cells from oxidative stress caused by reactive oxygen species (ROS) like hydrogen peroxide ($H_2O_2$). 1. **Why Sulphydryl is Correct:** The functional "business end" of glutathione is the **sulphydryl (–SH) group** provided by the amino acid **Cysteine**. In its reduced state (GSH), the –SH group acts as an electron donor to neutralize free radicals. During this process, two molecules of GSH are oxidized to form a disulfide-linked dimer (GSSG). The enzyme **Glutathione Peroxidase** facilitates this reaction, while **Glutathione Reductase** regenerates GSH using NADPH as a cofactor. 2. **Why Other Options are Incorrect:** * **Serine:** Contains a hydroxyl (–OH) group, not a thiol group, and is not a component of glutathione. * **Tyrosine:** An aromatic amino acid involved in signaling and hormone synthesis (e.g., Thyroxine, Catecholamines), but it does not provide the redox potential required for glutathione’s function. * **Acetyl-CoA:** This is a central metabolic intermediate in the TCA cycle and fatty acid synthesis, not a structural component of glutathione. **Clinical Pearls for NEET-PG:** * **NADPH Source:** The NADPH required to keep glutathione in its reduced state is primarily supplied by the **HMP Shunt (G6PD enzyme)**. * **G6PD Deficiency:** A deficiency in G6PD leads to low NADPH, resulting in oxidized glutathione. This leaves RBCs vulnerable to oxidative damage, leading to **Heinz bodies** and hemolytic anemia. * **Paracetamol Poisoning:** N-acetylcysteine (NAC) is the antidote for acetaminophen toxicity because it replenishes glutathione stores by providing cysteine.

Question 68: Growth retardation, taste alteration, hepatosplenomegaly, hypochromic microcytic anemia, hair loss, and hypogonadism in a boy indicate a deficiency of which of the following?

A. Selenium
B. Copper
C. Zinc (Correct Answer)
D. Iron

Explanation: **Explanation:** The clinical presentation described is a classic manifestation of **Zinc deficiency**. Zinc is an essential trace element required for the function of over 300 enzymes (e.g., Carbonic anhydrase, Alcohol dehydrogenase, Alkaline phosphatase). **Why Zinc is the correct answer:** * **Growth & Development:** Zinc is crucial for DNA synthesis and cell division; deficiency leads to **growth retardation** and **hypogonadism** (delayed sexual maturation). * **Taste (Dysgeusia):** Zinc is a component of **gustin**, a protein involved in taste bud development. * **Dermatological/Hair:** It is vital for skin integrity and hair follicle cycling, leading to **alopecia** and periorificial dermatitis (Acrodermatitis enteropathica). * **Hematology:** While less common than iron deficiency, chronic zinc deficiency can interfere with heme synthesis and iron metabolism, contributing to anemia and hepatosplenomegaly. **Why incorrect options are wrong:** * **Selenium:** Deficiency primarily causes **Keshan disease** (cardiomyopathy) or Kashin-Beck disease (osteoarthropathy), not growth retardation or taste loss. * **Copper:** Deficiency leads to **Menkes Kinky Hair Syndrome**, microcytic anemia (refractory to iron), and neurological symptoms, but is not typically associated with hypogonadism. * **Iron:** While it causes microcytic anemia, it does not typically cause taste alterations (except pica), hypogonadism, or significant hair loss in this specific constellation. **NEET-PG High-Yield Pearls:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder of zinc absorption presenting with the triad of alopecia, diarrhea, and vesiculobullous dermatitis. * **Enzyme Marker:** Serum **Alkaline Phosphatase** levels often decrease in zinc deficiency as it is a zinc-dependent metalloenzyme. * **Wound Healing:** Zinc is essential for collagen synthesis; deficiency leads to poor wound healing.

Question 69: What is the recommended daily supplement of vitamin D3 for females?

A. 200-500 IU
B. 500-1000 IU
C. 1000-2000 IU (Correct Answer)
D. 2000-2500 IU

Explanation: **Explanation:** The recommended daily allowance (RDA) for Vitamin D has evolved significantly due to the high prevalence of Vitamin D deficiency globally. For adult females (including pregnant and lactating women), the current clinical guidelines (Endocrine Society and various Indian health consensus statements) recommend a daily maintenance dose of **1000–2000 IU** to maintain optimal serum 25-hydroxyvitamin D [25(OH)D] levels above 30 ng/mL. * **Why Option C is correct:** While the basic RDA for bone health was traditionally lower (600 IU), clinical practice and recent metabolic studies suggest that 1000–2000 IU is necessary to achieve the pleiotropic benefits of Vitamin D, including immune modulation and muscle strength, especially in populations with limited sun exposure. * **Why Options A & B are incorrect:** Doses below 1000 IU (200–500 IU or 500–1000 IU) are often insufficient to correct or prevent deficiency in adults, particularly in the Indian context where skin pigmentation and pollution hinder endogenous synthesis. * **Why Option D is incorrect:** While 2000–2500 IU is safe, it is generally considered the upper end of the maintenance range or used for specific therapeutic correction rather than the standard baseline recommendation for all healthy females. **High-Yield NEET-PG Pearls:** * **Active Form:** 1,25-dihydroxyvitamin D3 (Calcitriol). * **Storage Form:** 25-hydroxyvitamin D (Calcidiol) – this is the form measured to check for deficiency due to its longer half-life. * **Toxicity:** Vitamin D is a fat-soluble vitamin; excessive intake can lead to hypercalcemia, hypercalciuria, and metastatic calcification. The "Tolerable Upper Limit" is generally cited as 4000 IU/day. * **Synthesis:** Occurs in the skin via UV-B radiation acting on 7-dehydrocholesterol.

Question 70: Crystallization and storage of insulin requires which ion?

A. Mn++
B. Zn++ (Correct Answer)
C. Cu++
D. Ca++

Explanation: **Explanation:** The correct answer is **Zn++ (Zinc)**. **Why Zinc is Correct:** Insulin is synthesized in the pancreatic β-cells as a monomer, but for efficient storage within secretory granules, it must be stabilized. Zinc ions play a crucial role in this process by coordinating with six insulin molecules to form a **zinc-insulin hexamer**. This hexameric structure is the stable, crystalline form in which insulin is stored. When blood glucose levels rise, these hexamers are released into the blood, where they rapidly dissociate into active monomers. **Why Other Options are Incorrect:** * **Mn++ (Manganese):** While manganese is a cofactor for enzymes like pyruvate carboxylase and superoxide dismutase, it has no structural role in insulin crystallization. * **Cu++ (Copper):** Copper is essential for enzymes like cytochrome c oxidase and superoxide dismutase, but it does not participate in insulin storage. * **Ca++ (Calcium):** While calcium ions are vital for the **exocytosis** (release) of insulin granules from the β-cells, they are not the primary ions responsible for the internal crystallization and structural storage of the hormone. **Clinical Pearls for NEET-PG:** * **Hexameric vs. Monomeric:** Rapid-acting insulin analogs (e.g., Lispro, Aspart) are designed to resist hexamer formation, allowing for faster absorption. * **Lente/Ultralente Insulins:** These pharmacological preparations use high zinc concentrations to promote crystallization, thereby delaying absorption and extending the duration of action. * **C-peptide:** It is stored in the same granules as the insulin hexamer and is released in equimolar amounts, serving as a marker for endogenous insulin production.

Practice by Chapter

Macronutrients and Energy Requirements

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Protein Quality and Nitrogen Balance

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Essential Amino Acids and Proteins

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Essential Fatty Acids and Lipids

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Dietary Fiber and Complex Carbohydrates

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Glycemic Index and Glycemic Load

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Micronutrients: Vitamins and Minerals

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Trace Elements and Metabolism

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Malnutrition: Biochemical Consequences

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Dietary Antioxidants

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Functional Foods and Nutraceuticals

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Dietary Guidelines and Recommendations

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