Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 151: Which protein is known as the reference protein?

A. Milk (Correct Answer)
B. Soyabean
C. Orange
D. Potato

Explanation: **Explanation:** The concept of a **Reference Protein** refers to a protein that contains all essential amino acids in the optimal proportions required by the human body for growth and maintenance. **Why Milk is the Correct Answer:** In nutritional biochemistry, **Milk protein (specifically Egg protein and Milk protein)** is considered a reference protein because it has a high biological value (BV) and a Net Protein Utilization (NPU) score near 100. These proteins are almost completely absorbed and utilized by the body. While Egg is often cited as the "gold standard" reference protein in many textbooks, **Milk** is the correct choice among the given options as it provides a complete amino acid profile with high bioavailability. **Analysis of Incorrect Options:** * **B. Soyabean:** Although it is the richest plant source of protein, it is deficient in sulfur-containing amino acids like **Methionine**. Plant proteins are generally "incomplete" compared to animal sources. * **C. Orange:** Oranges are primarily a source of Vitamin C and carbohydrates; their protein content is negligible. * **D. Potato:** While potatoes contain high-quality protein (Tuberin), the total quantity is too low (approx. 2%) to serve as a primary reference source. **High-Yield NEET-PG Pearls:** * **Biological Value (BV):** Measures the proportion of absorbed protein retained in the body. Egg has a BV of 100. * **Limiting Amino Acids:** Pulses are deficient in **Methionine**, while Cereals are deficient in **Lysine**. * **Mutual Supplementation:** Combining cereals and pulses (e.g., Khichdi) provides a complete amino acid profile, a concept frequently tested in community medicine and biochemistry. * **Reference Protein Standard:** The FAO/WHO often uses the amino acid composition of **Egg or Milk** as the benchmark to calculate the "Chemical Score" of other foods.

Question 152: What is the major mineral component of bone?

A. Calcite
B. Hydroxyapatite (Correct Answer)
C. Calcium oxide
D. Calcium carbonate

Explanation: **Explanation:** The correct answer is **Hydroxyapatite**. Bone is a specialized connective tissue consisting of an organic matrix (primarily Type I collagen) and an inorganic mineral phase. The mineral component accounts for approximately 65-70% of bone weight and is primarily composed of a crystalline form of calcium phosphate known as **Hydroxyapatite**, with the chemical formula **$\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2$**. These crystals align along collagen fibers to provide the skeleton with its characteristic compressive strength and structural rigidity. **Analysis of Options:** * **Calcite (A):** This is a stable polymorph of calcium carbonate found in the shells of marine organisms and limestone, but it is not a biological component of human bone. * **Calcium oxide (C):** Also known as quicklime, this is a caustic chemical used in industrial processes. It does not occur naturally in human tissues. * **Calcium carbonate (D):** While small amounts of carbonate are incorporated into the hydroxyapatite lattice as impurities, pure calcium carbonate is the primary component of eggshells and antacid tablets, not the structural mineral of bone. **High-Yield Clinical Pearls for NEET-PG:** * **Mineralization:** The process of depositing hydroxyapatite into the organic matrix is regulated by **alkaline phosphatase**, which increases local phosphate concentrations. * **Fluorosis:** Fluoride ions can replace the hydroxyl (-OH) groups in hydroxyapatite to form **Fluoroapatite**, which is more resistant to acid dissolution (relevant in dental caries prevention). * **Vitamin D:** Essential for bone health as it maintains the calcium-phosphorus product necessary for the crystallization of hydroxyapatite. * **Bone Reservoir:** Hydroxyapatite serves as the body’s primary reservoir for calcium (99%) and phosphorus (85%).

Question 153: A person fed on only maize diet will develop:

A. Beri Beri
B. Scurvy
C. Pellagra (Correct Answer)
D. Epidemic dropsy

Explanation: **Explanation:** The correct answer is **Pellagra**. This occurs because maize (corn) is deficient in the essential amino acid **Tryptophan**, which serves as a precursor for the endogenous synthesis of **Niacin (Vitamin B3)**. Furthermore, the niacin present in maize exists in a bound form called **niacytin**, which is biologically unavailable for absorption in the human gut. A chronic reliance on a maize-only diet leads to niacin deficiency, manifesting as Pellagra. **Analysis of Options:** * **Pellagra (Correct):** Characterized by the "4 Ds": Dermatitis (Casal’s necklace distribution), Diarrhea, Dementia, and if untreated, Death. * **Beri Beri:** Caused by **Thiamine (Vitamin B1)** deficiency. It is typically associated with a diet consisting primarily of polished rice, not maize. * **Scurvy:** Caused by **Vitamin C (Ascorbic acid)** deficiency, usually due to a lack of fresh fruits and vegetables. * **Epidemic Dropsy:** This is a clinical condition caused by the consumption of mustard oil adulterated with **Argemone mexicana** oil, which contains the toxin sanguinarine. **High-Yield Clinical Pearls for NEET-PG:** * **The Tryptophan Connection:** Approximately 60 mg of Tryptophan is required to synthesize 1 mg of Niacin. * **Hartnup Disease:** An autosomal recessive disorder involving defective transport of neutral amino acids (including tryptophan), which clinically mimics Pellagra. * **Carcinoid Syndrome:** Can lead to secondary Pellagra because tryptophan is diverted away from niacin synthesis to produce excessive amounts of Serotonin. * **Traditional Processing:** Native populations who soak maize in lime (calcium hydroxide) do not develop Pellagra because the alkaline treatment releases the bound niacin.

Question 154: Which of the following are characteristic features of zinc deficiency?

A. Sexual infantilism, Poor growth, Poor wound healing
B. Sexual infantilism, Poor wound healing, Loss of libido (Correct Answer)
C. Sexual infantilism, Poor growth, Loss of libido
D. Sexual infantilism, Loss of libido

Explanation: Zinc is an essential trace element that acts as a cofactor for over 300 enzymes, including Carbonic Anhydrase, Alcohol Dehydrogenase, and DNA/RNA Polymerases. It plays a critical role in protein synthesis, cell division, and immune function. **Explanation of the Correct Answer:** The correct option is **B (Sexual infantilism, Poor wound healing, Loss of libido)**. * **Sexual Infantilism & Loss of Libido:** Zinc is vital for the development and function of reproductive organs. It is necessary for the synthesis of testosterone and the maturation of sperm. Deficiency leads to hypogonadism, delayed puberty (sexual infantilism), and decreased sex drive. * **Poor Wound Healing:** Zinc is a cofactor for enzymes involved in collagen synthesis and cell proliferation. Its deficiency impairs the inflammatory response and epithelialization, leading to delayed healing. **Analysis of Incorrect Options:** * **Options A & C:** While **Poor growth** (growth retardation) is indeed a feature of zinc deficiency, these options are considered less "complete" in the context of this specific question's focus on the classic triad of symptoms often tested in clinical vignettes involving adolescent or adult presentations. * **Option D:** This option is incomplete as it omits the dermatological/surgical hallmark of zinc deficiency: impaired wound healing. **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder causing severe zinc malabsorption, characterized by the triad of **Dermatitis** (periorificial and acral), **Diarrhea**, and **Alopecia**. * **Dysgeusia/Hypogeusia:** Loss or alteration of taste is a classic early sign of zinc deficiency. * **Immune Dysfunction:** Zinc deficiency leads to thymic atrophy and impaired T-cell function. * **Antidote:** Zinc supplementation is used in the management of **Wilson’s Disease** because it induces metallothionein in the gut, which sequesters copper and prevents its absorption.

Question 155: What is the preferred fuel source for the body during a fasting state?

A. Carbohydrates
B. Fats (Correct Answer)
C. Proteins
D. Amino acids

Explanation: **Explanation:** In the fasting state (post-absorptive phase), the body undergoes a metabolic shift to preserve glucose for glucose-dependent tissues like the brain and RBCs. As insulin levels drop and glucagon levels rise, **lipolysis** is stimulated in adipose tissue. Triglycerides are broken down into free fatty acids (FFAs) and glycerol. These FFAs become the **primary and preferred fuel source** for most peripheral tissues, including the liver and resting skeletal muscle, via beta-oxidation. **Why other options are incorrect:** * **Carbohydrates:** These are the preferred fuel in the **fed state**. During fasting, glycogen stores (liver glycogen) are rapidly depleted within 12–24 hours, making them an unsustainable primary source. * **Proteins/Amino acids:** These serve as a "fuel of last resort." While amino acids are used for **gluconeogenesis** to maintain blood glucose levels during fasting, the body actively tries to spare protein to preserve structural integrity and enzymatic function. Significant protein catabolism only occurs during prolonged starvation. **High-Yield Clinical Pearls for NEET-PG:** * **The Brain's Exception:** While the body prefers fats, the brain cannot oxidize FFAs (due to the blood-brain barrier). In prolonged fasting, the brain adapts to use **ketone bodies** (derived from fat metabolism). * **RBCs:** Red blood cells lack mitochondria and can *only* use glucose (anaerobic glycolysis), regardless of the fasting state. * **Hormone Sensitive Lipase (HSL):** This is the key regulatory enzyme that mobilizes fats during fasting, activated by glucagon and epinephrine. * **Respiratory Quotient (RQ):** During fasting, the RQ drops toward **0.7**, reflecting a shift from carbohydrate oxidation (RQ = 1.0) to fat oxidation.

Question 156: In marasmus, wasting is due to which of the following?

A. Prolonged dietary deficiency of calories
B. Prolonged dietary deficiency of protein
C. Excess catabolism of fat and muscle mass to provide energy
D. All of the above (Correct Answer)

Explanation: **Explanation:** Marasmus is a form of severe protein-energy malnutrition (PEM) characterized by a global deficiency of nutrients. The underlying pathophysiology involves a state of negative energy balance where the body adapts to starvation. 1. **Why Option D is correct:** Marasmus results from a **prolonged deficiency of both calories (energy) and protein (Option A & B)**. Unlike Kwashiorkor, where protein deficiency is disproportionately greater than calorie intake, Marasmus is "balanced" starvation. To compensate for the lack of exogenous fuel, the body enters a hypercatabolic state. It mobilizes endogenous stores, leading to the **excess catabolism of subcutaneous fat and skeletal muscle (Option C)** to provide amino acids for gluconeogenesis and fatty acids for energy. This results in the characteristic "skin and bones" appearance. 2. **Analysis of Options:** * **Option A & B:** These are the primary triggers. While Kwashiorkor is classically "Protein deficiency with adequate calories," Marasmus is "Total calorie deficiency." * **Option C:** This is the physiological mechanism of wasting. The body sacrifices muscle mass to maintain blood glucose levels for vital organ function. **High-Yield Clinical Pearls for NEET-PG:** * **Appearance:** "Old man's face" or "Monkey-like facies" due to loss of buccal pads of fat. * **Edema:** Absent in Marasmus (present in Kwashiorkor due to hypoalbuminemia). * **Growth:** Severe growth retardation and "baggy pants" appearance (loose skin folds over buttocks). * **Key Difference:** Marasmus = Starvation (Calorie + Protein); Kwashiorkor = Protein deficiency + Stress/Infection.

Question 157: What is Intrinsic Factor related to?

A. Cobalamin absorption (Correct Answer)
B. Vitamin D
C. Folate absorption
D. Vitamin C

Explanation: **Explanation:** **Intrinsic Factor (IF)** is a glycoprotein secreted by the **parietal cells** of the gastric mucosa (stomach). Its primary physiological role is the absorption of **Vitamin B12 (Cobalamin)**. The process occurs in stages: 1. Dietary B12 is released from proteins by gastric acid and binds to R-binders (haptocorrin). 2. In the duodenum, pancreatic proteases digest R-binders, allowing B12 to bind to Intrinsic Factor. 3. The **IF-B12 complex** travels to the **terminal ileum**, where it binds to specific receptors (Cubilin) for absorption into the portal circulation. **Analysis of Incorrect Options:** * **Vitamin D:** Absorption is dependent on bile salts and micelle formation in the proximal small intestine, as it is a fat-soluble vitamin. * **Folate absorption:** Occurs primarily in the **jejunum** via the Proton-Coupled Folate Transporter (PCFT); it does not require Intrinsic Factor. * **Vitamin C:** A water-soluble vitamin absorbed in the ileum and jejunum via sodium-dependent active transport (SVCT1 and 2). **Clinical Pearls for NEET-PG:** * **Pernicious Anemia:** An autoimmune destruction of parietal cells leading to IF deficiency, resulting in Vitamin B12 deficiency and megaloblastic anemia. * **Site of Absorption:** Remember the "Rule of B": **B**12 is absorbed in the **B**ottom (Terminal Ileum). * **Schilling Test:** Historically used to determine the cause of B12 malabsorption (though largely replaced by antibody testing). * **Post-Gastrectomy:** Patients require lifelong parenteral B12 supplementation because the source of IF (the stomach) has been removed.

Question 158: Goat's milk ingestion predisposes to deficiency of which nutrient?

A. Iron
B. Folate (Correct Answer)
C. Vitamin B12
D. All of the above

Explanation: **Explanation:** The correct answer is **Folate (Vitamin B9)**. **Why Folate is the correct answer:** Goat’s milk is notoriously deficient in folic acid compared to human or cow’s milk. It contains only about **6 μg/L** of folate, whereas cow’s milk contains approximately **50 μg/L**. Infants or individuals exclusively fed goat’s milk are at high risk of developing **megaloblastic anemia** due to this deficiency. Additionally, goat's milk is low in Vitamin B12 and Vitamin D, but the folate deficiency is the most clinically significant and frequently tested association. **Analysis of Incorrect Options:** * **Iron:** While all animal milks (cow, goat, and human) are relatively low in iron, goat’s milk is not specifically singled out for causing iron deficiency more than others. Iron deficiency usually occurs due to delayed weaning or excessive intake of cow's milk (which can cause occult GI bleeding). * **Vitamin B12:** Although goat’s milk is lower in B12 than cow’s milk, the deficiency is not as profound or as "classic" a clinical association as folate deficiency in the context of goat's milk ingestion. * **All of the above:** While goat's milk has several nutritional gaps, the question specifically targets the most characteristic deficiency associated with its ingestion in medical literature and exams. **High-Yield Clinical Pearls for NEET-PG:** * **"Goat Milk Anemia":** Always associate this term with **Megaloblastic Anemia** caused by **Folate deficiency**. * **Heat Sensitivity:** Folate is heat-labile; boiling goat's milk further reduces its already low folate content. * **Comparison:** Cow's milk is low in Iron; Goat's milk is low in Folate; Human milk is the gold standard but requires Vitamin D and Iron supplementation after 6 months.

Question 159: A patient receiving total parenteral nutrition is at risk of developing which of the following nutrient deficiencies?

A. Vitamin B12
B. Folic acid
C. Vitamin B6
D. Zinc (Correct Answer)

Explanation: **Explanation:** **Correct Option: D (Zinc)** Patients on Total Parenteral Nutrition (TPN) are at a high risk of trace element deficiencies, most notably **Zinc**. Zinc is primarily absorbed in the small intestine; in TPN patients, the bypass of the gastrointestinal tract, coupled with increased urinary losses and high metabolic demands, leads to rapid depletion. * **Clinical Presentation:** Zinc deficiency in TPN patients typically manifests as **acrodermatitis enteropathica-like lesions** (periorificial and acral dermatitis), alopecia, impaired wound healing, and altered taste (hypogeusia). **Why Incorrect Options are Wrong:** * **A & B (Vitamin B12 and Folic Acid):** These are water-soluble vitamins that are standard components of routine parenteral multivitamin formulations (e.g., MVI-12). While B12 stores in the liver can last for years, folate stores last for months; however, acute deficiency is rare in TPN unless they are omitted from the daily infusion. * **C (Vitamin B6):** Pyridoxine is also routinely supplemented in TPN solutions. Isolated deficiency is uncommon compared to the rapid onset of trace element depletion like Zinc. **NEET-PG High-Yield Pearls:** * **Most common trace element deficiency in TPN:** Zinc. * **Chromium deficiency in TPN:** Presents as **glucose intolerance** (insulin resistance) because chromium is a component of the Glucose Tolerance Factor. * **Copper deficiency in TPN:** Presents as microcytic anemia and neutropenia (resembling Vitamin B12 deficiency but with normal B12 levels). * **Selenium deficiency in TPN:** Can lead to **cardiomyopathy** (Keshan-like disease) and muscle pain.

Question 160: Oral iron pills or iron injections are best absorbed when taken with which of the following?

A. High doses of Vitamin A
B. High doses of Vitamin C (Correct Answer)
C. High doses of Essential fatty acids
D. High doses of Vitamin D

Explanation: **Explanation:** The correct answer is **High doses of Vitamin C (Ascorbic acid)**. **Mechanism of Action:** Iron absorption occurs primarily in the duodenum and proximal jejunum. Dietary iron exists in two forms: Heme and Non-heme. Non-heme iron is usually in the **Ferric (Fe³⁺)** state, which is insoluble and cannot be absorbed. Vitamin C acts as a potent reducing agent that converts Ferric (Fe³⁺) iron into the **Ferrous (Fe²⁺)** state. The Ferrous form is more soluble and is the specific substrate for the **Divalent Metal Transporter 1 (DMT-1)** located on the apical membrane of enterocytes. Additionally, Vitamin C forms a chelate with iron in the acidic environment of the stomach, preventing it from precipitating in the alkaline environment of the small intestine. **Analysis of Incorrect Options:** * **Vitamin A:** While Vitamin A deficiency is linked to anemia (due to impaired mobilization of iron from stores), it does not directly facilitate the acute absorption of iron in the gut. * **Essential Fatty Acids:** These are vital for cell membrane integrity and prostaglandin synthesis but have no biochemical role in the reduction or transport of iron. * **Vitamin D:** Vitamin D is crucial for calcium and phosphorus homeostasis; it does not influence iron transporters or its oxidation state. **NEET-PG High-Yield Pearls:** * **Enhancers of Iron Absorption:** Vitamin C, Gastric Acid (HCl), and Amino acids (Cysteine). * **Inhibitors of Iron Absorption:** Phytates (cereals), Oxalates (spinach), Tannins (tea/coffee), Calcium, and Phosphates. * **Storage & Transport:** Iron is stored as **Ferritin** and transported in the blood by **Transferrin**. * **Hepcidin:** The key negative regulator of iron absorption; it degrades ferroportin.

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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