Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 171: What is the fuel value of fat in kilocalories per gram?

A. 4
B. 7
C. 9 (Correct Answer)
D. 5

Explanation: **Explanation:** The fuel value (caloric value) of a nutrient refers to the amount of energy released when one gram of that substance is oxidized in the body. **Why 9 kcal/g is correct:** Fats are the most energy-dense macronutrients. Chemically, fats (triacylglycerols) are highly reduced molecules with a very low proportion of oxygen compared to carbon and hydrogen. Because they are in a more reduced state, they undergo more extensive oxidation during metabolism, releasing **9 kcal/g** (37 kJ/g). Additionally, fats are stored in an anhydrous (water-free) state, unlike glycogen, making them the most efficient form of energy storage in the human body. **Analysis of Incorrect Options:** * **Option A (4 kcal/g):** This is the physiological fuel value for **Carbohydrates** and **Proteins**. While they are essential, they provide less than half the energy density of fat. * **Option B (7 kcal/g):** This is the caloric value of **Alcohol (Ethanol)**. While not a required nutrient, it contributes significantly to caloric intake in certain clinical scenarios. * **Option D (5 kcal/g):** This value does not correspond to a standard macronutrient fuel value, though it is sometimes cited as the approximate energy released per liter of oxygen consumed in a mixed diet. **High-Yield Clinical Pearls for NEET-PG:** * **Respiratory Quotient (RQ):** The RQ for fat is **0.7**, which is lower than carbohydrates (1.0) because more oxygen is required to oxidize the highly reduced carbon atoms in fatty acids. * **Specific Dynamic Action (SDA):** Also known as the Thermic Effect of Food, SDA is highest for proteins (30%), followed by carbohydrates (5-6%), and lowest for **fats (2-3%)**. * **Storage:** 1 gram of glycogen binds approximately 2 grams of water, whereas fat is stored pure, explaining why fat is the preferred long-term energy reserve.

Question 172: Anemia is caused by deficiency of which micronutrient?

A. Iron (Correct Answer)
B. Potassium
C. Phosphorus
D. Nickel

Explanation: **Explanation:** **1. Why Iron is the Correct Answer:** Iron is an essential micronutrient required for the synthesis of **heme**, the prosthetic group of **hemoglobin (Hb)**. Hemoglobin is the protein in red blood cells (RBCs) responsible for transporting oxygen from the lungs to the tissues. A deficiency in iron leads to impaired hemoglobin synthesis, resulting in **Microcytic Hypochromic Anemia**. This is the most common nutritional deficiency worldwide and a high-yield topic for NEET-PG. **2. Why the Other Options are Incorrect:** * **B. Potassium:** This is a major intracellular cation. Deficiency (hypokalemia) typically manifests as muscle weakness, cardiac arrhythmias, and paralytic ileus, but not anemia. * **C. Phosphorus:** Essential for bone mineralization and ATP production. Deficiency (hypophosphatemia) can cause muscle weakness and rickets/osteomalacia, but is rarely a primary cause of anemia. * **D. Nickel:** This is an ultra-trace element. While it may play a role in certain enzyme reactions, its deficiency is not clinically recognized as a cause of anemia in humans. **3. Clinical Pearls for NEET-PG:** * **Morphology:** Iron deficiency anemia (IDA) is characterized by a **low MCV (<80 fL)** and **low MCHC**. * **Laboratory Gold Standard:** A **low Serum Ferritin** level is the most sensitive and specific biochemical marker for diagnosing iron deficiency. * **Total Iron Binding Capacity (TIBC):** In IDA, TIBC is **increased**, while serum iron and transferrin saturation are decreased. * **Pica:** A classic clinical sign where patients crave non-nutritive substances (e.g., ice, clay, or dirt).

Question 173: What is the primary source of linoleic acid?

A. Vanaspati
B. Coconut oil
C. Sunflower oil (Correct Answer)
D. Palm oil

Explanation: **Explanation:** **Linoleic acid** is an essential omega-6 polyunsaturated fatty acid (PUFA) that the human body cannot synthesize. It serves as the precursor for arachidonic acid, which is vital for prostaglandin and leukotriene synthesis. **Why Sunflower Oil is Correct:** Vegetable seed oils are the richest sources of linoleic acid. **Sunflower oil** contains approximately 60-70% linoleic acid, making it one of the most concentrated dietary sources. Other rich sources include safflower oil, corn oil, and soybean oil. **Analysis of Incorrect Options:** * **Vanaspati (A):** This is hydrogenated vegetable oil. The process of hydrogenation converts unsaturated fats into saturated fats and creates **trans-fatty acids**, significantly reducing the linoleic acid content. * **Coconut Oil (B):** This is a highly **saturated fat** (approx. 90% saturated). It primarily contains medium-chain triglycerides (MCTs) like lauric acid and is very poor in PUFAs like linoleic acid (approx. 2%). * **Palm Oil (D):** While it contains more unsaturated fat than coconut oil, it is roughly 50% saturated (palmitic acid) and 40% monounsaturated (oleic acid). Its linoleic acid content (approx. 10%) is much lower than that of sunflower oil. **High-Yield Clinical Pearls for NEET-PG:** * **Essential Fatty Acids (EFA):** Linoleic acid (ω-6) and Linolenic acid (ω-3) are the two primary EFAs. * **Deficiency:** EFA deficiency leads to **Phrynoderma** (follicular hyperkeratosis/toad skin) and poor wound healing. * **P/S Ratio:** For a healthy diet, the Polyunsaturated to Saturated fat ratio should be above 0.5. Sunflower oil helps maintain a high P/S ratio. * **Hypocholesterolemic effect:** PUFAs like linoleic acid help lower LDL cholesterol by increasing the expression of LDL receptors.

Question 174: Chromium deficiency may lead to which of the following?

A. Insulin dysfunction (Correct Answer)
B. Cardiomyopathy
C. Endocarditis
D. External ophthalmoplegia

Explanation: **Explanation:** **1. Why Insulin Dysfunction is Correct:** Chromium (specifically the trivalent form, $Cr^{3+}$) is an essential trace element that plays a critical role in carbohydrate and lipid metabolism. It functions as a component of **Chromodulin** (also known as Glucose Tolerance Factor or GTF). Chromodulin enhances the action of insulin by increasing the sensitivity of insulin receptors on target cells. Therefore, chromium deficiency leads to impaired glucose tolerance, insulin resistance, and a clinical picture mimicking Type 2 Diabetes Mellitus. **2. Why Other Options are Incorrect:** * **Cardiomyopathy:** This is characteristically associated with **Selenium deficiency** (Keshan disease). While severe Thiamine (Vitamin B1) deficiency can cause "Wet Beriberi" (high-output heart failure), chromium is not linked to primary myocardial pathology. * **Endocarditis:** This is an inflammatory/infectious condition of the heart valves, typically caused by bacteria (e.g., *Staphylococcus aureus*) or fungi, and is unrelated to trace element deficiencies. * **External Ophthalmoplegia:** This is a hallmark of **Thiamine (B1) deficiency** (Wernicke-Korsakoff syndrome) or certain mitochondrial myopathies. It is not a feature of chromium deficiency. **3. High-Yield Clinical Pearls for NEET-PG:** * **Chromodulin Mechanism:** It facilitates the binding of insulin to its receptor and stimulates tyrosine kinase activity. * **Trivalent vs. Hexavalent:** $Cr^{3+}$ is the nutritional form; $Cr^{6+}$ (Hexavalent) is industrial and highly toxic/carcinogenic. * **TPN Association:** Chromium deficiency is most commonly seen in patients on long-term **Total Parenteral Nutrition (TPN)** without adequate trace element supplementation. * **Key Deficiency Sign:** Unexplained hyperglycemia and weight loss in a patient on TPN.

Question 175: A child presents with growth retardation, hypogonadism, alopecia, and immunodeficiency. The child has a deficiency of which of the following nutrients?

A. Zinc (Correct Answer)
B. Vitamin A
C. Folic Acid
D. Cholecalciferol

Explanation: **Explanation:** The clinical presentation of **growth retardation, hypogonadism, alopecia, and immunodeficiency** 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, Alkaline phosphatase, Alcohol dehydrogenase). It plays a pivotal role in DNA synthesis, cell division, and protein synthesis, which explains why its deficiency primarily affects rapidly dividing cells (skin, immune system, and gonads). * **Why Zinc is correct:** Zinc is crucial for the "Zinc-finger motif" in transcription factors and for the activity of growth hormone. Deficiency leads to stunted growth, delayed sexual maturation (hypogonadism), impaired wound healing, and cell-mediated immune dysfunction. A specific genetic defect in zinc absorption leads to **Acrodermatitis Enteropathica**, characterized by periorificial and acral dermatitis. **Analysis of Incorrect Options:** * **Vitamin A:** Deficiency typically presents with ocular symptoms (Xerophthalmia, Night blindness/Nyctalopia) and Bitot’s spots, not hypogonadism. * **Folic Acid:** Deficiency leads to Megaloblastic anemia and neural tube defects in newborns, but does not cause alopecia or hypogonadism. * **Cholecalciferol (Vitamin D):** Deficiency leads to Rickets in children (characterized by bone deformities like bow legs and rachitic rosary) and Osteomalacia in adults. **NEET-PG High-Yield Pearls:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder of the *SLC39A4* gene causing severe zinc malabsorption. * **Zinc & Insulin:** Zinc is required for the storage of insulin in the β-cells of the pancreas. * **Wound Healing:** Zinc is a cofactor for collagenase, making it vital for tissue repair.

Question 176: Which of the following is NOT a biological antioxidant that acts against free radicals formed inside the body?

A. Selenium
B. Glycine (Correct Answer)
C. Uric acid
D. Ascorbic acid

Explanation: **Explanation:** The body utilizes a complex defense system of **antioxidants** to neutralize reactive oxygen species (ROS) and free radicals, preventing oxidative stress and cellular damage. **Why Glycine is the correct answer:** Glycine is a non-essential amino acid. While it is a structural component of **Glutathione** (a major intracellular antioxidant), glycine itself does not possess the chemical properties to directly scavenge free radicals or act as a cofactor for antioxidant enzymes. Therefore, it is not classified as a biological antioxidant. **Analysis of incorrect options:** * **Selenium (Option A):** This is an essential trace element that acts as a vital cofactor for **Glutathione Peroxidase**, an enzyme that neutralizes hydrogen peroxide into water. * **Uric acid (Option C):** Often overlooked, uric acid is a potent endogenous antioxidant in human plasma. It accounts for over half of the total antioxidant capacity of blood by scavenging hydroxyl radicals and singlet oxygen. * **Ascorbic acid (Option D):** Also known as Vitamin C, it is a powerful water-soluble antioxidant. It directly neutralizes free radicals and is essential for regenerating Vitamin E (Tocopherol) from its oxidized form. **High-Yield NEET-PG Pearls:** * **Enzymatic Antioxidants:** Superoxide Dismutase (SOD - requires Zn, Cu, or Mn), Catalase (requires Heme/Iron), and Glutathione Peroxidase (requires Selenium). * **Non-Enzymatic Antioxidants:** Vitamin E (chain-breaking), Vitamin C, Vitamin A (Beta-carotene), Glutathione, and Bilirubin. * **Glutathione (GSH):** A tripeptide made of **Glutamate, Cysteine, and Glycine**. Cysteine provides the active -SH (sulfhydryl) group responsible for its antioxidant action.

Question 177: All the following affect the absorption of calcium, EXCEPT?

A. Citric acid
B. Retinoic acid (Correct Answer)
C. Phytates
D. Oxalates

Explanation: **Explanation:** Calcium absorption occurs primarily in the duodenum and jejunum via active transport (regulated by Vitamin D) and passive diffusion. The efficiency of this process is significantly influenced by dietary factors that either enhance or inhibit its solubility. **Why Retinoic Acid is the correct answer:** Retinoic acid is a metabolite of **Vitamin A**. While Vitamin A is essential for bone remodeling and osteoblast activity, it does **not** directly influence the intestinal absorption of calcium. In contrast, **Vitamin D (Calcitriol)** is the primary fat-soluble vitamin responsible for increasing calcium absorption by inducing the synthesis of Calbindin in intestinal mucosal cells. **Analysis of Incorrect Options:** * **Citric acid:** This is an **enhancer** of calcium absorption. Organic acids like citrate and ascorbate form soluble complexes with calcium, preventing it from precipitating and making it more available for absorption. * **Phytates:** Found in cereal grains, phytates are **inhibitors**. They form insoluble calcium-phytate complexes in the gut, which cannot be absorbed, leading to decreased bioavailability. * **Oxalates:** Found in spinach, rhubarb, and beets, oxalates are potent **inhibitors**. They bind to calcium to form insoluble calcium oxalate crystals, which are excreted in the feces. **Clinical Pearls for NEET-PG:** * **Promoters of Calcium Absorption:** Vitamin D, PTH, acidic pH (gastric HCl), lactose, and amino acids (Lysine and Arginine). * **Inhibitors of Calcium Absorption:** Phytates, oxalates, high dietary phosphate (decreases solubility), malabsorption syndromes (steatorrhea), and alkaline pH. * **High-Yield Fact:** The most active form of Vitamin D, **1,25-dihydroxycholecalciferol**, acts via nuclear receptors to increase the expression of **TRPV6** (calcium channels) and **Calbindin-D9k**.

Question 178: What is the recommended nitrogen to caloric ratio in total parenteral nutrition?

A. 1 gm of N2: 150 non-protein calories (Correct Answer)
B. 1 gm of N2: 100 non-protein calories
C. 1.25 gm of N2: 100 non-protein calories
D. 1.25 gm of K: 150 non-protein calories

Explanation: ### Explanation **The Concept of Nitrogen-Calorie Ratio** In Total Parenteral Nutrition (TPN), the goal is to provide adequate energy (calories) so that the administered amino acids are used for protein synthesis (anabolism) rather than being oxidized for energy. This is known as the **"Protein Sparing Action"** of carbohydrates and fats. The standard recommended ratio for a stable, non-stressed patient is **1 gm of Nitrogen for every 150 non-protein calories (NPC)**. * **Calculation Note:** Since 6.25 gm of protein contains approximately 1 gm of nitrogen, this ratio ensures that the body has enough non-protein energy (from glucose and lipids) to efficiently utilize the protein provided. **Analysis of Options:** * **Option A (Correct):** 1:150 is the gold standard ratio for maintenance in stable patients to achieve a positive nitrogen balance. * **Option B & C:** These ratios (1:100 or 1.25:100) represent a higher nitrogen density. While these may be used in **hypermetabolic states** (e.g., severe burns, sepsis, or multi-trauma) where protein requirements are significantly elevated, they are not the standard recommended baseline ratio. * **Option D:** This is a distractor; Potassium (K) requirements are calculated based on milliequivalents (mEq) per liter or per kcal, not as a primary ratio for nitrogen balance. **High-Yield Clinical Pearls for NEET-PG:** 1. **Nitrogen Content:** To convert protein (gm) to Nitrogen (gm), divide by **6.25**. 2. **Non-Protein Calories:** Only calories from Carbohydrates (3.4 kcal/g in TPN) and Fats (9 kcal/g) are counted in this ratio. 3. **Stress Levels:** * Normal/Stable: 1:150 * Moderately Stressed: 1:100 to 1:120 * Severely Stressed: 1:80 4. **Respiratory Quotient (RQ):** If the NPC ratio is too high in carbohydrates, the RQ increases (>1.0), which can make weaning from a ventilator difficult due to increased $CO_2$ production.

Question 179: Which amino acid is the limiting amino acid in Bengal gram?

A. Methionine (Correct Answer)
B. Lysine
C. Leucine
D. Tryptophan

Explanation: ### Explanation **1. Why Methionine is Correct:** In nutritional biochemistry, a **limiting amino acid** is the essential amino acid found in the shortest supply relative to the body's requirements in a specific food source. * **Pulses and Legumes** (including Bengal gram/Chickpea) are rich in Lysine but characteristically **deficient in sulfur-containing amino acids**, specifically **Methionine** and Cysteine. * Therefore, Methionine is the primary limiting amino acid in Bengal gram. **2. Analysis of Incorrect Options:** * **B. Lysine:** This is the limiting amino acid in **Cereals** (like wheat, rice, and maize). Pulses are actually used to supplement cereal-based diets because they are rich in Lysine. * **C. Leucine:** While present in various quantities, it is rarely the "limiting" factor in common plant proteins. However, an excess of Leucine in Jowar (Sorghum) can interfere with Tryptophan metabolism, leading to Pellagra. * **D. Tryptophan:** This is the limiting amino acid in **Maize** (along with Lysine). **3. High-Yield Clinical Pearls for NEET-PG:** * **Mutual Supplementation:** To achieve a "complete protein" profile, cereals (deficient in Lysine) and pulses (deficient in Methionine) are consumed together (e.g., Dal-Chawal or Khichdi). * **Limiting Amino Acid Summary Table:** * **Pulses/Legumes:** Methionine * **Cereals:** Lysine * **Maize:** Tryptophan and Lysine * **Egg/Milk:** No limiting amino acids (Reference proteins with Biological Value of 100 and 95 respectively). * **Biological Value (BV):** Pulses generally have a lower BV (~60) compared to animal proteins due to these limiting amino acids.

Question 180: The most frequent trace mineral deficiency developing in a patient receiving parenteral alimentation is a deficiency of which mineral?

A. Calcium
B. Chromium
C. Cobalt
D. Zinc (Correct Answer)

Explanation: **Explanation:** The correct answer is **Zinc**. Total Parenteral Nutrition (TPN) solutions, unless specifically supplemented, often lack adequate trace minerals. Zinc is the most common trace mineral deficiency in this setting because it is primarily absorbed in the small intestine and has significant losses through gastrointestinal secretions. Patients on TPN often have underlying malabsorption or chronic diarrhea, which further depletes zinc stores. **Why the other options are incorrect:** * **Calcium:** While electrolyte imbalances are common in TPN, calcium is a macro-mineral, not a trace mineral. It is routinely added to TPN formulations in significant quantities. * **Chromium:** Chromium deficiency can occur during long-term TPN and manifests as glucose intolerance (insulin resistance), but it is statistically much rarer than zinc deficiency. * **Cobalt:** Cobalt is a constituent of Vitamin B12. Isolated cobalt deficiency is not clinically recognized in humans; deficiency manifests as Vitamin B12 deficiency. **High-Yield Clinical Pearls for NEET-PG:** * **Zinc Deficiency Presentation:** Look for **Acrodermatitis Enteropathica** (periorificial and acral dermatitis), alopecia, diarrhea, impaired wound healing, and hypogeusia (decreased taste). * **Copper Deficiency:** The second most common trace mineral deficiency in TPN; presents with **microcytic anemia** (refractory to iron) and neutropenia. * **Selenium Deficiency:** Can lead to **Keshan disease** (cardiomyopathy) or skeletal muscle pain. * **Manganese/Copper Caution:** These are excreted via bile; they should be restricted in patients with obstructive jaundice to prevent toxicity.

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

Practice Questions

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