Nutrition and Metabolism — MCQs

A 52-year-old man presents with chronic diarrhea of several years' duration, now complicated by difficulty with night driving due to vision impairment. He is found to have microcytic anemia, a slight elevation in INR, low ionized calcium, and low albumin levels. What is the most likely underlying cause of his diarrhea?

Q47Easy

Metabolism of 100 grams of fat yields approximately how many kilocalories?

Q48Easy

Rice is deficient in which essential amino acid?

Q49Easy

Which of the following trace elements has a Vitamin E sparing effect?

Q50Medium

Which of the following correlates well to overcoming of limiting amino acids in the diet?

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 41: Soya bean contains protein to the tune of:

A. 20%
B. 40% (Correct Answer)
C. 60%
D. 80%

Explanation: **Explanation:** Soybean (*Glycine max*) is uniquely classified as both a pulse and an oilseed. It is recognized as the richest plant-based source of complete protein, containing all essential amino acids. **Why 40% is correct:** The average protein content of soybean ranges between **38% to 42%**. This high concentration is nearly double that of other common pulses (like grams or lentils) and significantly higher than animal sources like meat (20%) or eggs (13%). In addition to its 40% protein content, it contains approximately 20% fat (oil) and 30% carbohydrates. **Analysis of Incorrect Options:** * **A (20%):** This is the typical protein content of most other pulses (e.g., Bengal gram, Green gram) and meat. Soybean is significantly more concentrated. * **C & D (60% & 80%):** These values are physiologically impossible for a raw agricultural seed. Such high concentrations are only found in processed supplements like **Soy Protein Isolate**, which is manufactured to contain >90% protein. **High-Yield NEET-PG Pearls:** 1. **Limiting Amino Acid:** Like most legumes, soybean is deficient in **Methionine** (sulfur-containing amino acid) but rich in **Lysine**. It is often used to "supplement" cereal proteins (which are rich in Methionine but deficient in Lysine). 2. **Biological Value:** It has the highest biological value among plant proteins, often compared to casein (milk protein). 3. **Antinutritional Factors:** Raw soybean contains **Trypsin inhibitors**, which interfere with protein digestion. These are heat-labile and destroyed by proper cooking. 4. **Isoflavones:** Soy contains Genistein and Daidzein (phytoestrogens), which are studied for their role in reducing menopausal symptoms and lowering LDL cholesterol.

Question 42: Which amino acid is deficient in pulses?

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

Explanation: **Explanation:** In nutritional biochemistry, proteins are classified as "complete" or "incomplete" based on their essential amino acid profile. Most plant-based proteins are incomplete as they lack one or more essential amino acids, known as the **limiting amino acid**. **1. Why Methionine is the correct answer:** Pulses (legumes) are rich in lysine but are characteristically deficient in **sulfur-containing amino acids**, primarily **Methionine** and Cysteine. This is why a diet based solely on pulses cannot meet the body's total protein requirements for growth and repair. **2. Analysis of Incorrect Options:** * **Tryptophan (A):** This is the limiting amino acid in **Maize (Corn)**. A deficiency of tryptophan leads to Pellagra because tryptophan is a precursor for Niacin (Vitamin B3) synthesis. * **Lysine (B):** This is the limiting amino acid in **Cereals** (wheat, rice, maize). Interestingly, pulses are an excellent source of lysine, which is why the "cereal-pulse combination" (e.g., rice and dal) provides a complete amino acid profile. * **Leucine (D):** This is found in high amounts in **Sorghum (Jowar)**. An excess of leucine can interfere with tryptophan metabolism, potentially precipitating Pellagra. **High-Yield Clinical Pearls for NEET-PG:** * **Mutual Supplementation:** Combining cereals (deficient in lysine, rich in methionine) with pulses (deficient in methionine, rich in lysine) creates a **Complementary Protein** effect. * **Limiting Amino Acid Summary:** * **Pulses:** Methionine * **Cereals:** Lysine * **Maize:** Tryptophan and Lysine * **Reference Protein:** Egg protein is considered the "standard" or "complete" protein (Biological Value = 100) against which others are compared.

Question 43: Selenium deficiency causes which of the following conditions?

A. Cardiomyopathy (Correct Answer)
B. Neuropathy
C. Growth retardation
D. Rhabdomyolysis

Explanation: **Explanation:** **Correct Answer: A. Cardiomyopathy** Selenium is an essential trace element that functions as a cofactor for the enzyme **Glutathione Peroxidase**, which protects cells from oxidative damage by neutralizing hydrogen peroxide. A deficiency in Selenium leads to increased oxidative stress, particularly in cardiac myocytes. This manifests clinically as **Keshan Disease**, an endemic juvenile cardiomyopathy characterized by cardiac enlargement and heart failure. It is also associated with **Kashin-Beck disease**, a type of osteoarthropathy. **Analysis of Incorrect Options:** * **B. Neuropathy:** While Vitamin B1 (Thiamine), B6 (Pyridoxine), and B12 (Cobalamin) deficiencies are classic causes of peripheral neuropathy, Selenium deficiency does not typically present with neurological deficits. * **C. Growth retardation:** This is primarily associated with **Zinc deficiency** (along with acrodermatitis enteropathica and hypogonadism) or severe protein-energy malnutrition (Kwashiorkor). * **D. Rhabdomyolysis:** This is a clinical syndrome of muscle breakdown often caused by trauma, extreme exertion, or statin use. While Selenium deficiency can cause generalized muscle weakness (myopathy), it is not a primary cause of acute rhabdomyolysis. **High-Yield Facts for NEET-PG:** * **Enzyme Link:** Selenium is a vital component of **Selenocysteine**, found in Glutathione Peroxidase and **Thioredoxin reductase**. * **Thyroid Metabolism:** Selenium is also a cofactor for **Type 1 deiodinase**, which converts T4 to the active T3. * **Toxicity (Selenosis):** Excess selenium intake leads to garlic breath, hair loss (alopecia), and brittle nails. * **Key Association:** Always link Selenium deficiency to **Keshan Disease** (Cardiomyopathy) and **Kashin-Beck Disease** (Chondrodystrophy).

Question 44: What is the best index for calculating the nutritional value of protein?

A. Biological Value
B. Net protein utilization (Correct Answer)
C. Protein digestibility
D. Protein efficiency ratio

Explanation: ### Explanation The nutritional value of a protein depends on two factors: its amino acid composition and its digestibility. **Why Net Protein Utilization (NPU) is the best index:** NPU is considered the most comprehensive index because it accounts for both the **quality** (amino acid profile) and the **digestibility** of the protein. It is calculated as the percentage of ingested nitrogen that is retained in the body. * **Formula:** $NPU = \text{Biological Value (BV)} \times \text{Digestibility Coefficient}$. By incorporating digestibility, NPU provides a more accurate reflection of how much protein is actually available for metabolic use compared to Biological Value alone. **Analysis of Incorrect Options:** * **A. Biological Value (BV):** This measures the percentage of *absorbed* nitrogen retained by the body. While it assesses protein quality, it ignores the fraction of protein lost during digestion (fecal loss). * **C. Protein Digestibility:** This only measures how much of the ingested protein is absorbed into the bloodstream. It does not account for the essential amino acid balance or how well the body utilizes the absorbed protein. * **D. Protein Efficiency Ratio (PER):** This is the gain in body weight per gram of protein ingested (usually measured in rats). It is flawed because it assumes all weight gain is muscle/protein and does not account for maintenance needs. **High-Yield Clinical Pearls for NEET-PG:** * **Reference Protein:** Egg protein (Albumin) is the gold standard with a BV and NPU of approximately 100. * **Limiting Amino Acids:** Pulses are deficient in Methionine; Cereals are deficient in Lysine. * **PDCAAS (Protein Digestibility Corrected Amino Acid Score):** Currently the internationally "preferred" method for evaluating protein quality in human nutrition, though NPU remains the best traditional biological index.

Question 45: Which of the following micronutrients plays a role in the regulation of protein binding to DNA?

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

Explanation: **Explanation:** The correct answer is **Zinc**. Zinc plays a critical structural and functional role in the regulation of gene expression through the formation of **Zinc Finger Motifs**. These are the most common DNA-binding motifs found in eukaryotic transcription factors (e.g., steroid hormone receptors). In these motifs, a zinc ion is coordinated by cysteine and histidine residues, stabilizing a "finger-like" protein fold that fits precisely into the major groove of the DNA helix, allowing the protein to regulate transcription. **Why other options are incorrect:** * **Copper:** Primarily acts as a redox cofactor for enzymes like Cytochrome c oxidase, Superoxide Dismutase (SOD), and Lysyl oxidase. It is not involved in direct DNA-binding structural motifs. * **Selenium:** Essential for the antioxidant enzyme **Glutathione Peroxidase** and the conversion of T4 to T3 (Deiodinase). It does not regulate protein-DNA binding. * **Nickel:** While a trace element, its biological role in humans is minimal and primarily related to urease in certain bacteria; it has no established role in human DNA regulation. **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder causing zinc malabsorption, characterized by periorificial/acral dermatitis, alopecia, and diarrhea. * **Zinc & Wound Healing:** Zinc is a cofactor for **collagenase** (Matrix Metalloproteinases), making it vital for tissue repair. * **Dysgeusia:** Zinc deficiency is a classic cause of distorted sense of taste. * **DNA/RNA Polymerase:** Zinc is also a required cofactor for these enzymes, further emphasizing its role in nucleic acid metabolism.

Question 46: A 52-year-old man presents with chronic diarrhea of several years' duration, now complicated by difficulty with night driving due to vision impairment. He is found to have microcytic anemia, a slight elevation in INR, low ionized calcium, and low albumin levels. What is the most likely underlying cause of his diarrhea?

A. Malabsorption (Correct Answer)
B. Osmotic diarrhea
C. Secretory diarrhea
D. Inflammatory bowel disease

Explanation: ### Explanation The patient presents with a classic constellation of **fat-soluble and water-soluble vitamin deficiencies** secondary to chronic **malabsorption**. **Why Malabsorption is the Correct Answer:** Chronic diarrhea leading to multiple nutritional deficits is the hallmark of malabsorption syndrome. The clinical signs in this patient correlate directly with specific nutrient deficiencies: * **Difficulty with night driving (Nyctalopia):** Vitamin A deficiency. * **Elevated INR:** Vitamin K deficiency (impaired synthesis of clotting factors II, VII, IX, and X). * **Low Ionized Calcium:** Vitamin D deficiency (impaired calcium absorption). * **Microcytic Anemia:** Iron malabsorption. * **Low Albumin:** Protein malabsorption (hypoproteinemia). Since these deficiencies span multiple categories (fat-soluble vitamins, minerals, and macronutrients), a global process of malabsorption (e.g., Celiac disease, Chronic pancreatitis, or Tropical sprue) is the most likely etiology. **Why Other Options are Incorrect:** * **Osmotic Diarrhea:** Typically caused by non-absorbable solutes (like lactase deficiency). While it stops with fasting, it does not typically present with such profound, multi-systemic nutritional deficiencies unless part of a broader malabsorptive state. * **Secretory Diarrhea:** Characterized by high-volume watery stools that persist during fasting (e.g., Cholera, VIPoma). It primarily causes electrolyte imbalances rather than chronic fat-soluble vitamin deficiencies. * **Inflammatory Bowel Disease (IBD):** While Crohn’s can cause malabsorption, "Malabsorption" is the broader, more definitive physiological description of the *cause* of these specific clinical findings. IBD usually presents with systemic inflammatory markers, abdominal pain, or bloody stools. **NEET-PG High-Yield Pearls:** * **Vitamin A** is the first fat-soluble vitamin to become deficient in biliary obstruction or fat malabsorption. * **INR** is a sensitive marker for Vitamin K status; always check it in patients with chronic steatorrhea. * **D-Xylose Test:** Used to distinguish between mucosal malabsorption (e.g., Celiac) and pancreatic insufficiency.

Question 47: Metabolism of 100 grams of fat yields approximately how many kilocalories?

A. 200
B. 400
C. 600
D. 900 (Correct Answer)

Explanation: **Explanation:** The correct answer is **D (900)**. This is based on the physiological fuel values of macronutrients, which represent the amount of energy available to the body after digestion and absorption. 1. **Why 900 is correct:** Fat is the most energy-dense macronutrient. The standard physiological fuel value for fat is **9 kcal/gram**. Therefore, the metabolism of 100 grams of fat yields: * $100 \text{ g} \times 9 \text{ kcal/g} = \mathbf{900 \text{ kcal}}$. Fats provide more than double the energy of carbohydrates or proteins because they are more reduced (contain more carbon-hydrogen bonds), requiring more oxidation to produce $CO_2$ and $H_2O$. 2. **Why other options are incorrect:** * **Option B (400):** This represents the energy yield of 100 grams of **Carbohydrates** or **Proteins**. Both yield approximately **4 kcal/gram** ($100 \times 4 = 400$). * **Options A and C (200 and 600):** These values do not correspond to the standard metabolism of any single primary macronutrient in these quantities. **High-Yield Clinical Pearls for NEET-PG:** * **Respiratory Quotient (RQ):** Fat has an RQ of **0.7**, which is lower than carbohydrates (1.0) because fat requires more oxygen for its oxidation. * **Specific Dynamic Action (SDA):** Also known as the Thermic Effect of Food. Protein has the highest SDA (~30%), followed by carbohydrates (5–10%) and fats (0–3%). * **Energy Storage:** Fat is stored in anhydrous form in adipose tissue, making it the most efficient long-term energy reservoir in the human body. * **Alcohol:** Yields **7 kcal/gram**, placing its energy density between carbohydrates and fats.

Question 48: Rice is deficient in which essential amino acid?

A. Serine
B. Threonine (Correct Answer)
C. Methionine
D. Cysteine

Explanation: **Explanation:** In nutritional biochemistry, cereals and pulses are characterized by their "limiting amino acids"—the essential amino acids present in the shortest supply relative to human requirements. **Why Threonine is correct:** While most medical textbooks traditionally emphasize **Lysine** as the primary limiting amino acid in all cereals (including rice, wheat, and maize), **Threonine** is recognized as the **second limiting amino acid** in rice. In many competitive exams like NEET-PG, when Lysine is not provided in the options, Threonine is the established correct answer for rice deficiency. **Analysis of Incorrect Options:** * **Serine:** This is a non-essential amino acid synthesized from 3-phosphoglycerate; it is not a limiting factor in dietary proteins. * **Methionine & Cysteine:** These are sulfur-containing amino acids. While they are the limiting amino acids in **pulses/legumes**, they are generally present in adequate amounts in cereals like rice. **High-Yield Clinical Pearls for NEET-PG:** * **Cereals (Rice/Wheat):** Deficient in Lysine (1st) and Threonine (2nd). * **Pulses (Legumes):** Deficient in Methionine and Cysteine. * **Maize (Corn):** Deficient in Lysine and **Tryptophan**. (Note: Tryptophan deficiency in maize leads to Pellagra because it is a precursor for Niacin/Vitamin B3). * **Mutual Supplementation:** This is the nutritional strategy of combining cereals and pulses (e.g., Rice and Dal) to provide a complete amino acid profile, as the deficiency of one is compensated by the other.

Question 49: Which of the following trace elements has a Vitamin E sparing effect?

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

Explanation: **Explanation:** The correct answer is **Selenium (D)**. This relationship is a classic example of nutrient synergy in the body's antioxidant defense system. **Why Selenium is correct:** Selenium and Vitamin E function together to protect cells from oxidative damage caused by free radicals. * **Vitamin E (Tocopherol)** is a lipid-soluble antioxidant that acts within cell membranes to prevent the peroxidation of polyunsaturated fatty acids (PUFAs) by neutralizing free radicals. * **Selenium** is an essential component of the enzyme **Glutathione Peroxidase (GPx)**. This enzyme converts harmful hydrogen peroxide and lipid hydroperoxides into harmless water and alcohols. By reducing the overall load of peroxides in the cell, Selenium decreases the "workload" of Vitamin E. Consequently, adequate Selenium levels reduce the requirement for Vitamin E, a phenomenon known as the **"Vitamin E sparing effect."** **Why other options are incorrect:** * **Copper (A) and Iron (B):** Both are transition metals that can actually promote oxidative stress via the **Fenton reaction**, which generates highly reactive hydroxyl radicals. They do not spare Vitamin E; in excess, they may increase the demand for antioxidants. * **Magnesium (C):** While essential for over 300 enzymatic reactions (mostly involving ATP), Magnesium does not have a direct synergistic antioxidant relationship with Vitamin E. **High-Yield Clinical Pearls for NEET-PG:** * **Glutathione Peroxidase:** Contains Selenium in the form of **Selenocysteine** (the 21st amino acid). * **Keshan Disease:** A cardiomyopathy caused by Selenium deficiency. * **Synergy:** Both Vitamin E and Selenium are required to prevent conditions like hepatic necrosis and muscular dystrophy in animal models. * **Antioxidant Trio:** Remember that Vitamin E (membranes), Vitamin C (cytosol), and Selenium (enzyme cofactor) form the primary defense against lipid peroxidation.

Question 50: Which of the following correlates well to overcoming of limiting amino acids in the diet?

A. Rancidity
B. Tertiary structure of proteins
C. Biological value
D. Complementary action of proteins (Correct Answer)

Explanation: ### Explanation **1. Why "Complementary action of proteins" is correct:** Most plant-based proteins are "incomplete proteins" because they lack one or more essential amino acids, known as **limiting amino acids**. For example, cereals (wheat, rice) are deficient in **Lysine** but rich in Methionine, while pulses (dal, beans) are deficient in **Methionine** but rich in Lysine. **Complementary action** refers to the dietary practice of combining two or more incomplete protein sources (e.g., Rice and Dal) in the same meal. The amino acid provided by one food compensates for the deficiency in the other, resulting in a "complete" protein profile that supports optimal growth and nitrogen balance. **2. Why other options are incorrect:** * **Rancidity:** This refers to the oxidation or hydrolysis of fats/oils leading to unpleasant odors and tastes; it is unrelated to amino acid profiles. * **Tertiary structure of proteins:** This describes the three-dimensional folding of a single polypeptide chain. While it determines a protein's function, it does not address the nutritional deficiency of specific amino acids. * **Biological value (BV):** This is a measure of the proportion of absorbed protein that is retained by the body for growth and maintenance. While BV is a *measure* of protein quality, it does not describe the *mechanism* of overcoming limiting amino acids. **3. High-Yield Clinical Pearls for NEET-PG:** * **Limiting Amino Acid Pairs:** * Cereals: Limited by **Lysine**. * Pulses: Limited by **Methionine** (and Cysteine). * Maize: Limited by **Tryptophan** and Lysine (leads to Pellagra-like symptoms because Tryptophan is a precursor for Niacin). * **Reference Protein:** Egg protein is considered the "standard" or "reference protein" with a Biological Value of 100. * **Net Protein Utilization (NPU):** This is the most practical index for evaluating dietary protein quality as it accounts for both digestibility and biological value.

Practice by Chapter

Macronutrients and Energy Requirements

Practice Questions

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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