Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 11: Which of the following is the best method to assess the state of protein nutrition?

A. Mid Arm Circumference
B. Serum Albumin (Correct Answer)
C. Serum Transferrin
D. Total Body Nitrogen

Explanation: **Explanation:** Assessment of nutritional status is a critical component of clinical biochemistry. **Serum Albumin** is considered the most common and practical laboratory method to assess long-term protein nutrition. It reflects the liver's capacity for protein synthesis and the adequacy of dietary protein intake. Because albumin has a relatively long half-life (approx. 20 days), it serves as an excellent marker for **chronic protein malnutrition** (e.g., Kwashiorkor). **Analysis of Options:** * **Serum Albumin (Correct):** It is the "gold standard" in routine clinical practice for monitoring visceral protein stores over time. Low levels are strongly associated with increased morbidity and mortality. * **Mid Arm Circumference (MAC):** This is an anthropometric measure used to estimate skeletal muscle mass. While useful for rapid field screening of Protein-Energy Malnutrition (PEM) in children, it is less precise than biochemical markers for overall protein status. * **Serum Transferrin:** This is a visceral protein with a shorter half-life (8–10 days) than albumin. While it responds faster to changes, its levels are heavily influenced by iron deficiency, making it an unreliable primary marker for protein nutrition. * **Total Body Nitrogen:** While this is technically the most accurate "gold standard" for measuring total body protein, it requires **Neutron Activation Analysis**, which is expensive, involves radiation, and is only available in specialized research settings. It is not a practical "best method" for clinical assessment. **High-Yield Pearls for NEET-PG:** * **Shortest Half-life:** Retinol-binding protein (~12 hours) > Pre-albumin/Transthyretin (2 days) > Transferrin (8 days) > Albumin (20 days). * **Acute Changes:** **Pre-albumin** is the best marker for monitoring *acute* changes or the effectiveness of short-term nutritional therapy. * **Negative Acute Phase Reactant:** Albumin levels drop during inflammation/sepsis regardless of nutritional status; always correlate with C-Reactive Protein (CRP).

Question 12: Which mineral possesses antioxidant properties?

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

Explanation: **Explanation:** **Selenium (Option B)** is the correct answer because it is a vital trace element that functions as a cofactor for several antioxidant enzymes. Its primary antioxidant role is as a constituent of **Glutathione Peroxidase (GPx)**, which neutralizes hydrogen peroxide and lipid hydroperoxides, thereby protecting cell membranes from oxidative damage. Selenium is incorporated into these proteins as the unique amino acid **Selenocysteine**. **Analysis of Incorrect Options:** * **Molybdenum (Option A):** Functions as a cofactor for enzymes like Xanthine Oxidase and Sulfite Oxidase. It is involved in purine metabolism and sulfur detoxification rather than direct antioxidant defense. * **Copper (Option C) & Zinc (Option D):** While both are components of **Superoxide Dismutase (Cu-Zn SOD)**, they are generally classified as structural or catalytic cofactors. In the context of NEET-PG, when a single mineral is defined by its "antioxidant property," Selenium is the classic high-yield answer due to its exclusive role in the glutathione system. **High-Yield Clinical Pearls for NEET-PG:** * **Keshan Disease:** A cardiomyopathy resulting from Selenium deficiency (often seen in regions with selenium-poor soil). * **Kashin-Beck Disease:** An osteoarthropathy associated with Selenium deficiency. * **Iodine Link:** Selenium is also a component of **Type 1 Deiodinase**, essential for converting T4 to the active T3 hormone. * **Antioxidant Trio:** Remember the "ACES" (Vitamins A, C, E, and Selenium) as the primary nutritional antioxidant defense system.

Question 13: Which disease is associated with an excessive maize diet?

A. Wernicke's encephalopathy
B. Pellagra (Correct Answer)
C. Beri-Beri
D. Scurvy

Explanation: **Explanation:** The correct answer is **Pellagra**. This condition is caused by a deficiency of **Niacin (Vitamin B3)** or its precursor amino acid, **Tryptophan**. **Why Maize leads to Pellagra:** A diet predominantly consisting of maize (corn) is associated with Pellagra for two primary reasons: 1. **Low Tryptophan:** Maize is inherently deficient in Tryptophan, which the body normally converts into Niacin (60 mg of Tryptophan yields 1 mg of Niacin). 2. **Bound Niacin (Niacytin):** The Niacin present in maize is chemically bound to complex carbohydrates and proteins, making it biologically unavailable for absorption in the gut. **Analysis of Incorrect Options:** * **Wernicke's encephalopathy & Beri-Beri:** Both are caused by a deficiency of **Thiamine (Vitamin B1)**. Beri-Beri is classically associated with a diet of **polished rice**, not maize. * **Scurvy:** Caused by a deficiency of **Vitamin C (Ascorbic acid)**, typically due to a lack of fresh fruits and vegetables. **High-Yield Clinical Pearls for NEET-PG:** * **The 4 D’s of Pellagra:** Dermatitis (Casal’s necklace distribution), Diarrhea, Dementia, and Death. * **Hartnup Disease:** An autosomal recessive disorder involving defective transport of neutral amino acids (Tryptophan), which clinically presents as Pellagra-like symptoms. * **Carcinoid Syndrome:** Can lead to secondary Pellagra because Tryptophan is diverted toward the excessive production of Serotonin rather than Niacin. * **Traditional Processing:** Native Americans avoided Pellagra by treating maize with lime (calcium hydroxide), a process called *Nixtamalization*, which releases the bound Niacin.

Question 14: A 45-year-old male, a known case of hypertension under treatment, presents for a routine checkup. Which of the following fatty acids is advisable for him to include in a balanced diet?

A. Omega-3 fatty acids (Correct Answer)
B. Omega-6 fatty acids
C. Omega-9 fatty acids
D. Fatty acids are not necessary in the diet

Explanation: **Explanation:** **1. Why Omega-3 Fatty Acids are Correct:** Omega-3 fatty acids (α-linolenic acid, EPA, and DHA) are essential polyunsaturated fatty acids (PUFAs) with significant cardioprotective benefits. In a hypertensive patient, Omega-3s help reduce blood pressure by improving endothelial function, increasing nitric oxide bioavailability, and reducing systemic inflammation. They are precursors to **Series-3 Prostaglandins** and **Series-5 Leukotrienes**, which are less inflammatory and possess anti-thrombotic properties, thereby reducing the risk of cardiovascular events. **2. Analysis of Incorrect Options:** * **Omega-6 Fatty Acids (Option B):** While essential (e.g., Linoleic acid), an excess of Omega-6 relative to Omega-3 can be pro-inflammatory. They are precursors to **Series-2 Prostaglandins** and **Series-4 Leukotrienes**, which promote platelet aggregation and vasoconstriction. * **Omega-9 Fatty Acids (Option C):** These are monounsaturated fatty acids (e.g., Oleic acid). While healthy (found in olive oil), they are **non-essential** because the human body can synthesize them. They do not offer the same potent anti-inflammatory and anti-hypertensive benefits as Omega-3s. * **Fatty acids are not necessary (Option D):** This is physiologically incorrect. Essential fatty acids (EFAs) cannot be synthesized by the body due to the absence of desaturase enzymes ($\Delta$12 and $\Delta$15) and must be obtained from the diet for membrane integrity and eicosanoid synthesis. **Clinical Pearls for NEET-PG:** * **Essential Fatty Acids:** Linoleic acid ($\omega$-6) and $\alpha$-Linolenic acid ($\omega$-3). * **P/S Ratio:** A high Polyunsaturated to Saturated fatty acid ratio is recommended to lower serum cholesterol. * **Fish Oil:** Rich in EPA (Eicosapentaenoic acid) and DHA (Docosahexaenoic acid), which lower plasma triglycerides. * **Trans-fatty acids:** Most harmful; they increase LDL and decrease HDL.

Question 15: Aspartame contains which of the following amino acids?

A. Phenylalanine (Correct Answer)
B. Histidine
C. Tryptophan
D. Tyrosine

Explanation: **Explanation:** **Aspartame** is a low-calorie artificial sweetener widely used in the food industry. Chemically, it is a **methyl ester of a dipeptide**, consisting of two amino acids: **L-aspartic acid** and **L-phenylalanine**. 1. **Why Phenylalanine is Correct:** Upon ingestion, aspartame is broken down in the GI tract into its constituent parts: aspartate, phenylalanine, and methanol. Because it releases phenylalanine, it is a significant clinical concern for patients with **Phenylketonuria (PKU)**. These individuals lack the enzyme *phenylalanine hydroxylase* and cannot metabolize this amino acid, leading to toxic accumulation and intellectual disability. This is why products containing aspartame must carry a warning label for "Phenylketonurics." 2. **Why Other Options are Incorrect:** * **Histidine, Tryptophan, and Tyrosine:** These are not components of the aspartame molecule. While they are essential or semi-essential amino acids involved in various metabolic pathways (e.g., Tryptophan is a precursor for Serotonin; Tyrosine for Catecholamines), they do not form the chemical structure of this specific sweetener. **High-Yield Clinical Pearls for NEET-PG:** * **Composition:** Aspartyl-phenylalanine-1-methyl ester. * **Caloric Value:** It provides 4 kcal/g (same as proteins), but because it is ~200 times sweeter than sucrose, it is used in negligible amounts. * **Heat Lability:** Aspartame is **heat-unstable**; it loses its sweetness upon heating, making it unsuitable for baking. * **Methanol Toxicity:** A minor byproduct of aspartame metabolism is methanol, though the amount produced in dietary doses is generally considered sub-toxic.

Question 16: Which of the following are semi-essential amino acids?

A. Lysine
B. Leucine
C. Arginine and Lysine
D. Arginine and Histidine (Correct Answer)

Explanation: **Explanation:** Amino acids are classified based on their nutritional requirement into essential, non-essential, and semi-essential categories. **Why Arginine and Histidine are correct:** Semi-essential amino acids (also known as conditionally essential) are those that can be synthesized by the body, but the rate of synthesis is **insufficient** to meet the demands during periods of rapid growth, such as childhood, pregnancy, or recovery from severe illness. * **Arginine and Histidine** are the two primary semi-essential amino acids. While adults can synthesize enough Arginine through the urea cycle to maintain nitrogen balance, infants and growing children require dietary supplementation to support tissue growth and development. **Analysis of Incorrect Options:** * **A & B (Lysine and Leucine):** These are **purely essential** amino acids. The human body lacks the biochemical pathways to synthesize their carbon skeletons; therefore, they must be obtained entirely from the diet. (Note: Leucine is also one of the two purely ketogenic amino acids). * **C (Arginine and Lysine):** While Arginine is semi-essential, Lysine is strictly essential, making this combination incorrect. **NEET-PG High-Yield Pearls:** 1. **Mnemonic for Essential Amino Acids:** "PVT TIM HALL" (Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine). 2. **Purely Ketogenic:** Leucine and Lysine (The "L"s). 3. **Both Glucogenic & Ketogenic:** Phenylalanine, Tyrosine, Tryptophan, Isoleucine (The "PIT" amino acids). 4. **Arginine** is a precursor for Nitric Oxide (NO), Urea, and Creatine. 5. **Histidine** is the precursor for Histamine (via decarboxylation).

Question 17: Acrodermatitis enteropathica is due to deficiency of which essential trace element?

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

Explanation: **Explanation:** **Acrodermatitis enteropathica (AE)** is a rare autosomal recessive disorder caused by a mutation in the **SLC39A4 gene**, which encodes the **ZIP4 transporter**. This protein is essential for the intestinal absorption of **Zinc**. 1. **Why Zinc is correct:** Zinc is a vital cofactor for over 300 enzymes (e.g., Alkaline Phosphatase, Carbonic Anhydrase). Its deficiency leads to the classic triad of AE: **periorificial and acral dermatitis** (skin rash around the mouth, anus, and limbs), **alopecia**, and **diarrhea**. It also causes impaired wound healing and immune dysfunction. 2. **Why other options are incorrect:** * **Manganese:** Deficiency is extremely rare but may lead to impaired growth and skeletal abnormalities. Toxicity (Manganism) presents with Parkinson-like neurological symptoms. * **Copper:** Deficiency causes **Menkes disease** (kinky hair, connective tissue defects) or microcytic anemia. It is a cofactor for Lysyl oxidase and Tyrosinase. * **Selenium:** Deficiency leads to **Keshan disease** (cardiomyopathy) or Kashin-Beck disease (osteoarthritis). It is a key component of the antioxidant enzyme **Glutathione peroxidase**. **High-Yield Clinical Pearls for NEET-PG:** * **Zinc & Vitamin A:** Zinc is required for the synthesis of Retinol-Binding Protein (RBP); thus, zinc deficiency can mimic Vitamin A deficiency (night blindness). * **Diagnosis:** Low serum zinc levels and low serum **Alkaline Phosphatase** (a zinc-dependent enzyme). * **Treatment:** Lifelong oral zinc supplementation (usually Zinc Sulfate). * **Acquired AE:** Can occur in infants during weaning from breast milk to formula or in adults with severe malabsorption/TPN.

Question 18: Which of the following has the highest protein content?

A. Mutton
B. Soyabean (Correct Answer)
C. Egg
D. Milk

Explanation: **Explanation:** The protein content of food is determined by the grams of protein present per 100 grams of the edible portion. In the context of nutritional biochemistry, **Soyabean** is recognized as the richest plant-based source of protein. **Why Soyabean is Correct:** Soyabean contains approximately **40–43% protein** (40-43g per 100g). It is unique among plant sources because it is a "complete protein," containing all essential amino acids in sufficient quantities, making it a vital meat substitute in vegetarian diets. **Analysis of Incorrect Options:** * **Mutton:** Contains roughly **18–22% protein**. While it has a high biological value (BV), the total quantity per 100g is significantly lower than that of soyabean. * **Egg:** Contains about **13% protein**. However, the egg is considered the "Reference Protein" (Gold Standard) because it has a Biological Value of 100 and a Net Protein Utilization (NPU) of nearly 100%, meaning its amino acid profile perfectly matches human requirements. * **Milk:** Contains only **3.2–3.5% protein**. Although it is a high-quality protein (casein and whey), its high water content results in a low protein density per 100g. **High-Yield NEET-PG Pearls:** * **Highest Protein Content:** Soyabean (~40%). * **Reference Protein:** Egg (due to highest Biological Value). * **Limiting Amino Acids:** Pulses are generally deficient in **Methionine**, while Cereals are deficient in **Lysine**. Soyabean is an exception with a superior profile. * **Biological Value (BV) Order:** Egg (100) > Milk (95) > Meat (74) > Soyabean (74) > Pulses (50-60). Note that while Soyabean has more *quantity*, Egg has better *quality*.

Question 19: All of the following statements about Net Protein Utilization (NPU) are true EXCEPT:

A. NPU is defined as (Nitrogen retained / Nitrogen consumed) x 100.
B. NPU is useful for estimating protein quality.
C. Egg protein has the highest NPU value.
D. One gram of protein is equivalent to one gram of Nitrogen. (Correct Answer)

Explanation: ### Explanation **1. Why Option D is the Correct Answer (The False Statement)** In nutritional biochemistry, protein and nitrogen are not equivalent in weight. Proteins, on average, contain approximately **16% nitrogen**. Therefore, to calculate the amount of nitrogen in a protein sample, the weight of the protein is divided by **6.25** (since 100/16 = 6.25). * **Correct conversion:** 6.25 grams of protein = 1 gram of Nitrogen. **2. Analysis of Other Options** * **Option A:** This is the standard formula for NPU. It measures the percentage of dietary nitrogen that is actually retained by the body for growth and maintenance. * **Option B:** NPU is a superior index for estimating protein quality compared to Biological Value (BV) because it accounts for **digestibility**. (NPU = BV × Digestibility coefficient). * **Option C:** Egg protein (whole egg) is considered the "reference protein" or "gold standard" in nutrition. It has an NPU value of approximately **94–100**, the highest among natural food sources. **3. High-Yield Clinical Pearls for NEET-PG** * **Biological Value (BV):** Measures nitrogen retained vs. nitrogen *absorbed*. Unlike NPU, it does not account for digestive losses. * **Reference Protein:** Egg is used as the standard (BV = 100, NPU = 100). * **Limiting Amino Acids:** Pulses are deficient in Methionine; Cereals are deficient in Lysine. * **Nitrogen Balance:** * *Positive:* Growth, pregnancy, convalescence. * *Negative:* Starvation, severe burns, uncontrolled diabetes, wasting diseases.

Question 20: Iron absorption is decreased by which of the following?

A. Calcium
B. Tetracycline
C. Phytate
D. Ascorbic acid (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Ascorbic acid** **Mechanism of Iron Absorption:** Iron is absorbed in the proximal duodenum in its ferrous ($Fe^{2+}$) state. Dietary iron often exists in the ferric ($Fe^{3+}$) state, which is insoluble and cannot be absorbed. **Ascorbic acid (Vitamin C)** is a potent reducing agent that converts $Fe^{3+}$ to $Fe^{2+}$. It also forms a soluble iron-ascorbate complex that prevents the precipitation of iron in the alkaline environment of the small intestine. Therefore, Ascorbic acid **increases** iron absorption. **Analysis of Options:** * **A. Calcium:** Calcium is a known inhibitor of both heme and non-heme iron absorption. It competes for transport mechanisms and interferes with the initial uptake into enterocytes. * **B. Tetracycline:** This antibiotic forms insoluble chelates with iron in the gastrointestinal tract, significantly **decreasing** the absorption of both the drug and the mineral. * **C. Phytates:** Found in cereals and legumes, phytates (and oxalates) bind to iron to form insoluble complexes, thereby **decreasing** its bioavailability. *(Note: The question asks which factor **decreases** absorption, but the provided key marks Ascorbic Acid as correct. In standard biochemistry, Calcium, Tetracycline, and Phytates **decrease** absorption, while Ascorbic Acid **increases** it. If the question intended to ask for the factor that **increases** absorption, D is correct.)* **High-Yield Clinical Pearls for NEET-PG:** * **Enhancers of Iron Absorption:** Ascorbic acid, Gastric HCl (maintains iron in $Fe^{2+}$ state), and "Meat Factor." * **Inhibitors of Iron Absorption:** Phytates, Oxalates, Phosphates (in milk), Tannins (in tea), Calcium, and Antacids. * **Hepcidin:** The master regulator of iron homeostasis; it decreases iron absorption by degrading **Ferroportin**. * **DMT-1 (Divalent Metal Transporter 1):** The primary transporter for non-heme iron ($Fe^{2+}$) into the enterocyte.

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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