Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 201: A 72-year-old woman, in otherwise good health, presents with megaloblastic anemia. Careful evaluation reveals a folate deficiency as the cause of the anemia. Assuming the folate deficiency is due to dietary causes, which of the following is the most likely problem?

A. Lack of leafy green vegetables
B. Lack of milk products
C. Lack of yellow vegetables
D. Overcooked food (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Overcooked food**. **1. Why "Overcooked food" is correct:** Folate (Vitamin B9) is highly **heat-labile**. It is sensitive to high temperatures and prolonged cooking processes. Boiling, steaming, or frying vegetables for extended periods can destroy up to 50% to 95% of the folate content. In elderly patients who may prefer soft, well-cooked meals, dietary folate deficiency often arises not from a lack of intake, but from the thermal destruction of the vitamin during food preparation. **2. Why the other options are incorrect:** * **A. Lack of leafy green vegetables:** While green leafy vegetables (like spinach) are the primary source of folate (derived from *folium*, meaning leaf), the question states the patient is in "otherwise good health." If she consumes these vegetables but overcooks them, the deficiency persists. * **B. Lack of milk products:** Milk is a poor source of folate. A lack of milk is more traditionally associated with Vitamin D or Calcium deficiencies, not megaloblastic anemia. * **C. Lack of yellow vegetables:** Yellow vegetables are rich in Vitamin A (Beta-carotene), not folate. Deficiency here would lead to night blindness or xerophthalmia. **3. NEET-PG High-Yield Pearls:** * **Storage:** Folate stores in the liver are limited (3–4 months), making deficiency appear much faster than Vitamin B12 deficiency (which takes 3–5 years). * **Absorption:** Folate is absorbed in the **jejunum** in the monoglutamate form. * **The "Folate Trap":** B12 deficiency leads to a functional folate deficiency because folate remains trapped as N5-methyl THF, unable to participate in DNA synthesis. * **Clinical Sign:** Look for **hypersegmented neutrophils** on a peripheral smear as an early sign of megaloblastic anemia.

Question 202: In the human body, which of the following trace elements is found in the same metabolic pathway or has a close functional relationship with iron?

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

Explanation: **Explanation:** The correct answer is **Zinc (B)**. The functional relationship between iron and zinc is primarily observed in the synthesis of heme. In the final step of heme biosynthesis, the enzyme **ferrochelatase** inserts ferrous iron ($Fe^{2+}$) into protoporphyrin IX. When iron is deficient, ferrochelatase utilizes zinc as an alternative substrate, leading to the formation of **Zinc Protoporphyrin (ZPP)**. Measuring ZPP levels is a clinically significant screening tool for iron deficiency anemia and lead poisoning. Furthermore, iron and zinc share common transporters in the duodenum (such as DMT1), leading to competitive inhibition during absorption. **Why other options are incorrect:** * **Calcium:** While calcium can inhibit iron absorption, it does not share a direct metabolic pathway or enzymatic co-factor relationship like zinc does in heme synthesis. * **Copper:** Copper is essential for iron *transport* (via ferroxidases like ceruloplasmin and hephaestin), but it is not substituted for iron in metabolic intermediates like zinc is. * **Selenium:** Selenium is a vital component of glutathione peroxidase and deiodinase enzymes; its metabolic pathways are distinct from the iron-porphyrin pathway. **High-Yield Clinical Pearls for NEET-PG:** * **Zinc Protoporphyrin (ZPP):** An elevated ZPP/Heme ratio is one of the earliest markers of iron-depleted erythropoiesis. * **Acrodermatitis Enteropathica:** An autosomal recessive disorder of zinc absorption characterized by periorificial dermatitis, alopecia, and diarrhea. * **Lead Poisoning:** Lead inhibits ferrochelatase, significantly increasing Zinc Protoporphyrin levels, which serves as a diagnostic marker.

Question 203: Which amino acid is cereals rich in?

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

Explanation: **Explanation:** In nutritional biochemistry, proteins are classified based on their amino acid profile. Cereals and pulses are complementary protein sources because they lack different essential amino acids. **1. Why Methionine is correct:** Cereals (such as wheat, rice, and maize) are generally **rich in sulfur-containing amino acids**, primarily **Methionine** and Cysteine. However, they are deficient in Lysine. This is why a diet combining cereals with pulses (which are rich in Lysine but poor in Methionine) provides a "complete protein" profile with a high biological value. **2. Analysis of Incorrect Options:** * **A. Lysine:** This is the **limiting amino acid** in cereals. It is the most common wrong answer choice; while cereals are "poor" in Lysine, pulses are "rich" in it. * **B. Threonine:** This is the second limiting amino acid in many cereals (especially rice and wheat). * **C. Tryptophan:** This is notably deficient in **Maize** (corn). A diet predominantly based on maize can lead to Pellagra because Tryptophan is a precursor for Niacin (Vitamin B3) synthesis. **High-Yield Clinical Pearls for NEET-PG:** * **Limiting Amino Acid:** The essential amino acid found in the smallest amount relative to the human requirement. * **Cereals:** Rich in Methionine; Deficient in Lysine. * **Pulses (Legumes):** Rich in Lysine; Deficient in Methionine. * **Maize:** Deficient in both Lysine and Tryptophan. * **Reference Protein:** Egg albumin is considered the "standard" or reference protein with a biological value of 100.

Question 204: In Kwashiorkor, which immunoglobulin is most affected?

A. IgD
B. IgA (Correct Answer)
C. IgE
D. IgM

Explanation: **Explanation:** In **Kwashiorkor** (protein-energy malnutrition characterized by edema), the immune system is significantly compromised. While total serum protein levels are low, the impact on specific immunoglobulins varies. **IgA** is the most affected because its production and secretion are highly dependent on the integrity of mucosal surfaces and the availability of specific amino acids. In malnutrition, there is marked atrophy of the mucosal-associated lymphoid tissue (MALT) and a decrease in secretory component synthesis, leading to a significant reduction in **Secretory IgA (sIgA)**. This explains why children with Kwashiorkor are highly susceptible to mucosal infections, such as gastroenteritis and respiratory tract infections. **Analysis of Options:** * **IgA (Correct):** It is the primary immunoglobulin of the mucosal immune system. Malnutrition leads to thymic atrophy and impaired mucosal immunity, specifically lowering IgA levels. * **IgD:** This is primarily a B-cell surface receptor. Its levels are generally very low in serum and are not a clinical marker for nutritional status. * **IgE:** Levels are often **elevated** rather than decreased in Kwashiorkor, primarily due to the high prevalence of concomitant parasitic (helminthic) infections in malnourished populations. * **IgM:** Serum levels of IgM (and often IgG) are usually maintained within normal limits or may even be elevated due to chronic underlying infections, despite the overall protein deficiency. **High-Yield Clinical Pearls for NEET-PG:** * **Edema in Kwashiorkor:** Primarily due to hypoalbuminemia (decreased oncotic pressure). * **Immune Status:** Kwashiorkor is often described as "nutritional AIDS" due to profound T-cell dysfunction and thymic atrophy. * **Fatty Liver:** Occurs due to decreased synthesis of **Apolipoprotein B-100**, preventing the export of triglycerides from the liver (VLDL formation).

Question 205: Which of the following is NOT an antioxidant?

A. Ceruloplasmin
B. Transferrin
C. Catalase
D. Elastase (Correct Answer)

Explanation: ### Explanation The correct answer is **D. Elastase**. **1. Why Elastase is the Correct Answer:** Antioxidants are substances that neutralize reactive oxygen species (ROS) or prevent their formation to protect cells from oxidative stress. **Elastase** is not an antioxidant; it is a **proteolytic enzyme** (serine protease) secreted by neutrophils and the pancreas. Its primary function is to break down elastin in the extracellular matrix. In the lungs, excessive elastase activity (often due to Alpha-1 Antitrypsin deficiency) leads to the destruction of alveolar walls, resulting in emphysema. **2. Analysis of Incorrect Options:** * **Ceruloplasmin (Option A):** This is a major copper-carrying plasma protein. It acts as an antioxidant by functioning as a **ferroxidase**, converting toxic ferrous iron ($Fe^{2+}$) to ferric iron ($Fe^{3+}$). This prevents the Fenton reaction, which otherwise generates highly reactive hydroxyl radicals. * **Transferrin (Option B):** This is an iron-transport protein. It acts as a **preventive antioxidant** by sequestering free iron. By binding iron tightly, it ensures that free metal ions are unavailable to catalyze the formation of free radicals. * **Catalase (Option C):** This is a potent **enzymatic antioxidant** found in peroxisomes. It catalyzes the decomposition of hydrogen peroxide ($H_2O_2$) into water and oxygen, protecting the cell from oxidative damage. **3. High-Yield Clinical Pearls for NEET-PG:** * **Classification:** Antioxidants are divided into **Enzymatic** (Superoxide Dismutase, Glutathione Peroxidase, Catalase) and **Non-enzymatic** (Vitamin E, Vitamin C, Glutathione, Uric acid). * **Chain Breaker:** Vitamin E ($\alpha$-tocopherol) is the most important lipid-soluble, chain-breaking antioxidant in cell membranes. * **Glutathione Peroxidase:** This enzyme requires **Selenium** as a cofactor, a frequent high-yield fact in biochemistry. * **Fenton Reaction:** $Fe^{2+} + H_2O_2 \rightarrow Fe^{3+} + OH^\bullet + OH^-$. Antioxidants like Transferrin and Ceruloplasmin specifically aim to inhibit this process.

Question 206: Which micronutrient is associated with rash and diarrhea?

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

Explanation: **Explanation:** **Zinc deficiency** is the classic cause of the clinical triad: **Dermatitis (rash), Diarrhea, and Alopecia.** The characteristic rash is known as **Acrodermatitis Enteropathica**, which presents as erythematous, vesiculobullous, and eczematous lesions typically located periorificially (around the mouth, anus) and on the extremities (acral distribution). Zinc is a vital cofactor for over 300 enzymes, including Carbonic Anhydrase and Alkaline Phosphatase, and is essential for cell division and mucosal integrity, explaining why its deficiency manifests in rapidly turnover tissues like the skin and gut. **Analysis of Incorrect Options:** * **Manganese:** Deficiency is extremely rare in humans but may lead to impaired growth, skeletal abnormalities, and defects in lipid/carbohydrate metabolism. Toxicity (Manganism) presents with Parkinsonian-like neurological symptoms. * **Copper:** Deficiency typically presents with **Microcytic Hypochromic Anemia** (refractory to iron), neutropenia, and skeletal demineralization. It does not typically cause the specific rash/diarrhea triad. * **Iron:** Deficiency primarily leads to **Microcytic Hypochromic Anemia**, pica, and koilonychia (spoon-shaped nails). While it can cause glossitis, it is not associated with acral dermatitis or chronic diarrhea. **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder involving a mutation in the **SLC39A4** gene, leading to impaired zinc absorption. * **Zinc & Wound Healing:** Zinc is crucial for collagen synthesis; deficiency leads to poor wound healing. * **Hypogonadism:** Chronic zinc deficiency is a known cause of delayed puberty and stunted growth. * **Taste Sensation:** Zinc is a component of **Gustin**; deficiency leads to decreased taste acuity (**Hypogeusia**).

Question 207: Tomatoes are rich in which of the following acids?

A. Citric acid (Correct Answer)
B. Oxalic acid
C. Acetic acid
D. Formic acid

Explanation: **Explanation:** **Correct Answer: A. Citric acid** Tomatoes are a significant source of organic acids, with **citric acid** being the most abundant (comprising approximately 90% of the total acid content). In biochemistry and nutrition, citric acid is a key intermediate in the **TCA cycle (Krebs cycle)**. Its presence in tomatoes contributes to their characteristic tartness and plays a role in enhancing the absorption of non-heme iron from the diet by maintaining it in the more soluble ferrous ($Fe^{2+}$) state. **Analysis of Incorrect Options:** * **B. Oxalic acid:** While tomatoes do contain trace amounts of oxalic acid, the concentration is much lower than citric acid. High levels of oxalic acid are typically associated with spinach, rhubarb, and beet greens. Clinically, oxalates are significant as they can bind calcium to form **calcium oxalate stones** in the urinary tract. * **C. Acetic acid:** This is the primary component of vinegar, produced through the fermentation of ethanol by *Acetobacter*. It is not naturally found in significant quantities in fresh tomatoes. * **D. Formic acid:** This is the simplest carboxylic acid, primarily found in the venom of ant stings and bee stings. It is toxic in high concentrations and is not a nutritional component of tomatoes. **High-Yield Clinical Pearls for NEET-PG:** * **Lycopene:** Tomatoes are the richest source of lycopene, a potent antioxidant carotenoid that has been linked to a reduced risk of prostate cancer. * **Vitamin C:** Tomatoes are also a major source of Ascorbic acid, essential for collagen synthesis (prolyl and lysyl hydroxylase cofactor). * **Iron Absorption:** The combination of citric acid and Vitamin C in tomatoes significantly enhances the bioavailability of dietary iron.

Question 208: Keshan disease is due to deficiency of?

A. Selenium (Correct Answer)
B. Chromium
C. Zinc
D. Iodine

Explanation: **Explanation:** **Keshan disease** is a congestive cardiomyopathy primarily affecting children and young women. It is caused by a deficiency of **Selenium**, often exacerbated by a viral infection (typically Coxsackievirus B). 1. **Why Selenium is Correct:** Selenium is an essential trace element incorporated into the enzyme **Glutathione Peroxidase**. This enzyme plays a critical role in neutralizing hydrogen peroxide and lipid hydroperoxides, protecting cardiac tissues from oxidative damage. In the absence of selenium, oxidative stress leads to myocardial necrosis and fibrosis, manifesting as Keshan disease. 2. **Why Other Options are Incorrect:** * **Chromium:** Deficiency is associated with **impaired glucose tolerance** and insulin resistance, as chromium is a component of the Glucose Tolerance Factor (GTF). * **Zinc:** Deficiency leads to **Acrodermatitis enteropathica**, growth retardation, delayed wound healing, and hypogonadism. * **Iodine:** Deficiency causes **Goiter** and **Cretinism** due to its role in thyroid hormone synthesis. **High-Yield Clinical Pearls for NEET-PG:** * **Kashin-Beck Disease:** Another selenium deficiency disorder characterized by osteoarthropathy (necrosis of joint cartilage). * **Selenocysteine:** Known as the **21st amino acid**, it is the form in which selenium is present in enzymes like Glutathione Peroxidase and Deiodinase (which converts T4 to T3). * **Toxicity:** Excess selenium (Selenosis) causes garlic breath, hair loss (alopecia), and brittle nails. * **Antioxidant Synergy:** Selenium works synergistically with **Vitamin E** to prevent lipid peroxidation.

Question 209: All of the following are reasons for impaired absorption of calcium except:

A. Inositol hexaphosphate in cereals
B. High intake of oxalate
C. High concentrations of fatty acids in the intestinal lumen
D. Decreased iron intake (Correct Answer)

Explanation: **Explanation:** Calcium absorption occurs primarily in the duodenum and jejunum via active transport (regulated by Vitamin D) and passive diffusion. The absorption is highly sensitive to the chemical environment of the intestinal lumen. **Why "Decreased iron intake" is the correct answer:** Iron and calcium are both divalent cations that compete for similar transport mechanisms (though iron primarily uses DMT-1). **High intake** of iron can interfere with calcium absorption, and conversely, high calcium can inhibit iron absorption. Therefore, **decreased iron intake** would theoretically **increase** or have a neutral effect on calcium bioavailability, rather than impairing it. **Analysis of Incorrect Options (Factors that impair absorption):** * **Inositol hexaphosphate (Phytic acid):** Found in cereals and grains, phytates form insoluble calcium-phytate complexes that cannot be absorbed by the intestine. * **High intake of oxalate:** Present in leafy greens (like spinach) and chocolate, oxalates bind to calcium to form insoluble **calcium oxalate** crystals, significantly reducing bioavailability. * **High concentrations of fatty acids:** In malabsorption syndromes (steatorrhea), unabsorbed fatty acids react with calcium to form insoluble **"calcium soaps."** This not only impairs calcium absorption but also increases free oxalate absorption (leading to enteric hyperoxaluria and renal stones). **High-Yield Clinical Pearls for NEET-PG:** * **Promoters of Calcium Absorption:** Vitamin D (Calcitriol), PTH, acidic pH (Gastrin/HCl), and certain amino acids (Lysine, Arginine). * **Inhibitors of Calcium Absorption:** Phytates, oxalates, high dietary fiber, phosphates, and malabsorption of fats. * **The "Soap" Connection:** In Crohn’s disease or Celiac disease, fat malabsorption leads to hypocalcemia and a high risk of calcium oxalate kidney stones.

Question 210: What is the richest source of cholesterol?

A. Egg (Correct Answer)
B. Hydrogenated oil
C. Butter
D. Cheese

Explanation: **Explanation:** **1. Why Egg is the Correct Answer:** Cholesterol is a sterol synthesized exclusively by animal tissues. Among common dietary sources, the **egg yolk** is the most concentrated source of cholesterol. A single large egg contains approximately **185–215 mg** of cholesterol. In medical biochemistry, eggs are often used as the "gold standard" for high cholesterol content per unit weight compared to other food groups. **2. Analysis of Incorrect Options:** * **Hydrogenated Oil:** These are plant-based oils (like vanaspati) that have undergone industrial hydrogenation. While they are high in **Trans-fats**, they contain **zero cholesterol** because plants do not synthesize cholesterol (they contain phytosterols like sitosterol instead). * **Butter:** Butter is a dairy fat containing significant cholesterol (approx. 215 mg per 100g). However, because we consume butter in smaller quantities compared to the bulk of an egg, and because the concentration per serving is lower than an egg yolk, it is considered the second-best source among these options. * **Cheese:** While cheese contains cholesterol, the amount varies by type (approx. 70–100 mg per 100g), making it a less concentrated source than egg yolk. **3. NEET-PG High-Yield Pearls:** * **Exogenous vs. Endogenous:** About 25% of body cholesterol comes from the diet (exogenous), while 75% is synthesized *de novo* (endogenous), primarily in the **liver and intestines**. * **Rate-Limiting Enzyme:** HMG-CoA Reductase is the key regulatory enzyme in cholesterol synthesis (target of Statins). * **Plant Sterols:** Sitosterol and Stigmasterol (found in vegetable oils) actually **inhibit** the intestinal absorption of dietary cholesterol. * **Daily Limit:** Traditional guidelines suggest a limit of 300 mg/day, though recent metabolic studies focus more on the impact of saturated and trans-fats on LDL levels rather than dietary cholesterol alone.

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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