Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 181: Cancer can be prevented by the ingestion of which of the following?

A. Beta carotene
B. Vitamin C and E
C. Selenium
D. All the above (Correct Answer)

Explanation: The correct answer is **D. All the above**. ### Educational Explanation The underlying medical concept is the **Antioxidant Defense System**. Cancer development is often initiated by oxidative stress, where **Reactive Oxygen Species (ROS)** and free radicals cause oxidative damage to DNA, leading to mutations and malignant transformations. Antioxidants neutralize these free radicals, thereby acting as chemopreventive agents. * **Beta-carotene (Vitamin A precursor):** It is a potent lipid-soluble antioxidant that quenches singlet oxygen. Epidemiological studies suggest it helps prevent epithelial cancers (like lung and skin cancer) by regulating cell differentiation and inhibiting lipid peroxidation. * **Vitamin C (Ascorbic Acid):** A water-soluble antioxidant that scavenges free radicals in the cytosol. It also prevents the formation of nitrosamines (potent carcinogens) in the stomach. * **Vitamin E (Tocopherol):** The primary antioxidant in cell membranes. It prevents the "chain reaction" of lipid peroxidation, protecting the integrity of the cell membrane from oxidative damage. * **Selenium:** This is an essential trace element that acts as a co-factor for the enzyme **Glutathione Peroxidase**. This enzyme converts hydrogen peroxide into water, preventing the formation of the highly reactive hydroxyl radical. ### High-Yield Clinical Pearls for NEET-PG * **The "Antioxidant Cocktail":** Vitamins A, C, E, and Selenium work synergistically. Vitamin C is known to regenerate Vitamin E from its oxidized form. * **Glutathione Peroxidase:** Remember that Selenium is the integral component of this enzyme (High-yield MCQ). * **Lycopene:** Another carotenoid (found in tomatoes) specifically linked to a reduced risk of **Prostate Cancer**. * **Caution:** While dietary antioxidants are protective, high-dose synthetic supplementation (especially Beta-carotene in heavy smokers) has paradoxically shown an increased risk of lung cancer in some trials (CARET study).

Question 182: Fiaky paint appearance of skin is seen in which condition?

A. Dermatitis
B. Pellagra
C. Marasmus
D. Kwashiorkor (Correct Answer)

Explanation: **Explanation** **Correct Answer: D. Kwashiorkor** Kwashiorkor is a form of Protein-Energy Malnutrition (PEM) characterized by a severe deficiency of dietary protein despite adequate calorie intake. The **"Flaky Paint Dermatosis"** (also known as "Crazy Pavement Dermatosis") is a pathognomonic clinical feature. It occurs due to hyperkeratosis and hyperpigmentation followed by desquamation. The skin becomes dry, atrophic, and peels off in scales, resembling old, sun-baked paint peeling off a wall. This typically affects areas of friction or pressure, such as the buttocks and lower limbs. **Analysis of Incorrect Options:** * **A. Dermatitis:** This is a general term for skin inflammation. While Kwashiorkor involves skin changes, "flaky paint" is a specific morphological description not used for general dermatitis. * **B. Pellagra:** Caused by Vitamin B3 (Niacin) deficiency, it presents with a symmetrical, photosensitive rash. A classic sign is **Casal’s necklace** (around the neck), but it is described as "gloves and stockings" pigmentation rather than flaky paint. * **C. Marasmus:** This is caused by a total deficiency of both proteins and calories. The skin in Marasmus is typically thin, dry, and wrinkled (due to loss of subcutaneous fat), giving the child an **"Old Man/Monkey Face"** appearance, but it does not exhibit the flaky paint sign. **High-Yield Clinical Pearls for NEET-PG:** * **Kwashiorkor:** Edema (due to hypoalbuminemia), Flag sign (alternating bands of hair color), and fatty liver (due to decreased apolipoprotein synthesis). * **Marasmus:** Severe muscle wasting, no edema, and no fatty liver. * **Key Differentiator:** The presence of **edema** is the hallmark that distinguishes Kwashiorkor from Marasmus.

Question 183: Which of the following are considered anti-carcinogens?

A. Carotenoids (Correct Answer)
B. Flavonoids
C. Curcumoids
D. Benzene

Explanation: **Explanation:** **1. Why Carotenoids are correct:** Carotenoids (such as $\beta$-carotene, lycopene, and lutein) are potent **antioxidants** and precursors to Vitamin A. They act as anti-carcinogens by neutralizing free radicals and reactive oxygen species (ROS), thereby preventing oxidative DNA damage. Furthermore, they enhance gap-junctional communication and modulate gene expression involved in cell cycle arrest and apoptosis, which inhibits the proliferation of malignant cells. **2. Analysis of other options:** * **Flavonoids & Curcuminoids:** While these compounds (found in soy and turmeric, respectively) are widely recognized for their antioxidant and anti-cancer properties in nutritional biochemistry, **Carotenoids** are the most classically cited "anti-carcinogens" in standard medical textbooks (like Harper’s Illustrated Biochemistry) specifically regarding their role in reducing the risk of epithelial cancers. * **Benzene:** This is a well-known **carcinogen**. Chronic exposure to benzene is strongly associated with bone marrow suppression and an increased risk of **Acute Myeloid Leukemia (AML)**. **3. High-Yield Clinical Pearls for NEET-PG:** * **Lycopene:** A specific carotenoid found in tomatoes, associated with a reduced risk of **prostate cancer**. * **The $\beta$-carotene Paradox:** While dietary carotenoids are protective, high-dose synthetic $\beta$-carotene supplements have been shown to *increase* the risk of lung cancer in heavy smokers (CARET study). * **Other Dietary Anti-carcinogens:** Vitamin C, Vitamin E, Selenium, and Isothiocyanates (found in cruciferous vegetables like broccoli). * **Aflatoxin B1:** A potent dietary carcinogen (from *Aspergillus flavus*) linked to **Hepatocellular Carcinoma**.

Question 184: Which micronutrient helps to increase the absorption of iron from the diet?

A. Folic acid
B. Ascorbic acid (Correct Answer)
C. Nicotinic acid
D. Pantothenic acid

Explanation: **Explanation:** The absorption of dietary iron occurs primarily in the duodenum and proximal jejunum. Dietary iron exists in two forms: **Heme iron** (from animal sources) and **Non-heme iron** (from plant sources). **Why Ascorbic Acid (Vitamin C) is correct:** Non-heme iron is usually found in the **Ferric state (Fe³⁺)**, which is insoluble and cannot be easily absorbed. Ascorbic acid facilitates iron absorption through two primary mechanisms: 1. **Reduction:** It acts as a potent reducing agent, converting Ferric iron (Fe³⁺) to the **Ferrous state (Fe²⁺)**, which is the form required for transport across the apical membrane via the Divalent Metal Transporter 1 (DMT1). 2. **Chelation:** It forms a soluble iron-ascorbate complex in the acidic environment of the stomach, preventing iron from precipitating as insoluble phosphates or phytates. **Why other options are incorrect:** * **Folic acid (B9):** Essential for DNA synthesis and erythropoiesis; its deficiency causes megaloblastic anemia, but it does not directly influence iron transport. * **Nicotinic acid (B3):** A precursor for NAD/NADP involved in redox reactions; it has no role in intestinal iron absorption. * **Pantothenic acid (B5):** A constituent of Coenzyme A; it is involved in fatty acid metabolism but not iron kinetics. **High-Yield Clinical Pearls for NEET-PG:** * **Enhancers of Iron Absorption:** Ascorbic acid, Gastric Acid (HCl), and Citrate. * **Inhibitors of Iron Absorption:** Phytates (cereals), Oxalates (spinach), Tannins (tea), Phosphates, and Calcium. * **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.

Question 185: Which fruit contains the maximum number of calories?

A. Banana (Correct Answer)
B. Mango
C. Orange
D. Pear

Explanation: **Explanation:** In the context of nutritional biochemistry, the caloric density of a fruit is primarily determined by its carbohydrate content (sugars and starches) and its water content. **Why Banana is the Correct Answer:** Among the common fruits listed, the **Banana** is the most energy-dense. It has a significantly lower water content compared to citrus fruits or pears and a higher concentration of carbohydrates. A medium-sized banana provides approximately **89–116 kcal per 100g**. It is rich in resistant starch (in unripe bananas) and simple sugars like sucrose, glucose, and fructose (in ripe bananas), making it a high-glycemic index food often used for rapid energy replenishment. **Analysis of Incorrect Options:** * **Mango:** While high in sugar and often considered "fattening," mangoes contain more water than bananas. They provide roughly **60–70 kcal per 100g**. * **Orange:** As a citrus fruit, oranges have a very high water content (approx. 87%). They are low-calorie fruits, providing only about **47 kcal per 100g**. * **Pear:** Pears are high in dietary fiber (pectin) and water, which lowers their caloric density. They provide approximately **57 kcal per 100g**. **High-Yield Clinical Pearls for NEET-PG:** * **Glycemic Index (GI):** Bananas have a moderate-to-high GI. Patients with Diabetes Mellitus are often advised to limit banana intake due to its high carbohydrate load. * **Potassium Content:** Bananas are a premier source of Potassium ($K^+$). This is clinically relevant in managing patients with hypertension or those on potassium-wasting diuretics. * **Energy Density:** In medical nutrition therapy, bananas are recommended for "catch-up growth" in protein-energy malnutrition (PEM) due to their high caloric density and digestibility.

Question 186: Which amino acid is deficient in rice?

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

Explanation: ### Explanation **Core Concept: Limiting Amino Acids in Cereals** In nutritional biochemistry, a "limiting amino acid" is the essential amino acid found in the smallest quantity in a specific food source, thereby limiting the body's ability to synthesize proteins. Cereals (like rice, wheat, and maize) are generally characterized by a deficiency in **Lysine**. **Why Option A is Correct:** Rice is a cereal grain. All cereals are deficient in the essential amino acid **Lysine**, but they are relatively rich in sulfur-containing amino acids like Methionine and Cysteine. Therefore, to achieve a "complete protein" profile, rice is traditionally consumed with pulses (dal), which are rich in Lysine but deficient in Methionine. **Why Other Options are Incorrect:** * **B. Methionine:** This is the limiting amino acid in **pulses/legumes**. Rice actually contains adequate amounts of Methionine, making it the perfect complementary protein source for lentils. * **C. Glutamic acid:** This is a non-essential amino acid and is generally abundant in most dietary proteins; it is not a limiting factor in rice. * **D. Tryptophan:** This is the classic limiting amino acid in **Maize (Corn)**. A diet solely based on maize can lead to Pellagra because Tryptophan is a precursor for Niacin (Vitamin B3) synthesis. **High-Yield NEET-PG Pearls:** 1. **Cereals:** Deficient in Lysine; Rich in Methionine. 2. **Pulses:** Deficient in Methionine; Rich in Lysine. 3. **Maize:** Deficient in both Lysine and Tryptophan. 4. **Reference Protein:** Egg albumin is considered the "standard" or reference protein (Biological Value = 100) against which other proteins are compared. 5. **Mutual Supplementation:** The practice of mixing cereals and pulses (e.g., Khichdi or Idli) ensures all essential amino acids are present, improving the overall **Net Protein Utilization (NPU)**.

Question 187: A chronic alcoholic patient on a high carbohydrate diet develops a deficiency of which of the following micronutrients?

A. Selenium
B. Cadmium
C. Manganese (Correct Answer)
D. Iodine

Explanation: ### Explanation **Correct Option: C (Manganese)** The correct answer is **Manganese**. Manganese (Mn²⁺) is a critical cofactor for several enzymes involved in carbohydrate and lipid metabolism. Specifically, it is required for **Pyruvate Carboxylase**, the enzyme that converts pyruvate to oxaloacetate in gluconeogenesis. In chronic alcoholics, nutritional intake is often poor, and a high carbohydrate diet significantly increases the metabolic demand for manganese-dependent enzymes. Chronic alcohol consumption also interferes with the intestinal absorption of manganese and increases its biliary excretion. Consequently, the combination of increased metabolic demand (due to high carbohydrate load) and decreased availability leads to a functional deficiency. **Analysis of Incorrect Options:** * **A. Selenium:** Selenium is a cofactor for **Glutathione Peroxidase**. While alcoholics may be deficient in antioxidants, selenium deficiency is primarily associated with Keshan disease (cardiomyopathy) and is not specifically exacerbated by a high carbohydrate diet. * **B. Cadmium:** Cadmium is a toxic heavy metal, not an essential micronutrient. It has no physiological role in carbohydrate metabolism. * **D. Iodine:** Iodine is essential for thyroid hormone synthesis. Its deficiency leads to goiter and hypothyroidism, unrelated to acute carbohydrate metabolism or chronic alcoholism. **Clinical Pearls for NEET-PG:** * **Manganese Toxicity:** Known as "Manganism," it presents with Parkinson-like symptoms (extrapyramidal signs) due to accumulation in the basal ganglia. It is an occupational hazard for miners. * **Enzyme Association:** Remember Manganese for **Pyruvate Carboxylase**, **Arginase** (Urea cycle), and **Manganese-Superoxide Dismutase (Mn-SOD)** in mitochondria. * **Alcoholism & Thiamine:** While Thiamine (B1) is the most common deficiency in alcoholics, this question specifically tests the mineral requirement for carbohydrate processing.

Question 188: Calorie restriction increases longevity through which mechanism?

A. Sirtuins (Correct Answer)
B. Albumin
C. Amyloid
D. Carotene

Explanation: **Explanation:** **Mechanism of Longevity (Sirtuins):** Calorie restriction (CR) is the most robust non-genetic intervention known to increase lifespan. The primary mediators of this effect are **Sirtuins (SIRT1-7)**, a family of NAD+-dependent deacetylases. When caloric intake is reduced, the **NAD+/NADH ratio increases**, which activates Sirtuins. * **Action:** Sirtuins deacetylate key transcription factors (like PGC-1α and FOXO), leading to enhanced DNA repair, increased mitochondrial biogenesis, reduced apoptosis, and improved insulin sensitivity. * **Result:** This metabolic shift mimics a "survival mode" that protects cells from oxidative stress and age-related decline. **Analysis of Incorrect Options:** * **Albumin:** This is the primary plasma protein responsible for maintaining oncotic pressure and transporting bilirubin/drugs. While it reflects nutritional status, it has no direct signaling role in the genetic regulation of longevity. * **Amyloid:** These are misfolded protein aggregates associated with pathology (e.g., Alzheimer’s disease, Systemic Amyloidosis). Amyloid accumulation is a feature of aging and disease, rather than a mechanism for extending life. * **Carotene:** A precursor to Vitamin A with antioxidant properties. While antioxidants help reduce free radical damage, they do not regulate the genetic pathways of longevity in the same systemic way that Sirtuins do. **High-Yield Clinical Pearls for NEET-PG:** * **Resveratrol:** A polyphenol found in red wine that is a potent activator of **SIRT1**, often cited as a "calorie restriction mimetic." * **AMPK:** Another key enzyme activated during calorie restriction; it works in tandem with Sirtuins to sense low energy states. * **mTOR Pathyway:** Calorie restriction **inhibits** mTOR (Mammalian Target of Rapamycin). Inhibition of mTOR is associated with increased autophagy and lifespan.

Question 189: Which of the following are the products of fermentation of dietary fibres in the colon?

A. Free radicals
B. Glycerol
C. Butyrate (Correct Answer)
D. Sucrose

Explanation: **Explanation:** Dietary fibers (non-starch polysaccharides like cellulose, hemicellulose, and pectin) are resistant to digestion in the human small intestine. When they reach the colon, they undergo anaerobic fermentation by the gut microbiota. **1. Why Butyrate is Correct:** The primary end-products of this microbial fermentation are **Short-Chain Fatty Acids (SCFAs)**. The three major SCFAs produced are **Acetate (2C), Propionate (3C), and Butyrate (4C)**. * **Butyrate** is particularly significant because it serves as the **primary energy source for colonocytes** (epithelial cells of the colon). It also plays a role in maintaining mucosal integrity and exhibits anti-inflammatory and anti-carcinogenic properties. **2. Why Incorrect Options are Wrong:** * **Free radicals (A):** Fermentation is a metabolic process that generally reduces oxidative stress in the gut; it does not primarily produce free radicals. * **Glycerol (B):** Glycerol is a product of triacylglycerol (fat) hydrolysis, not the fermentation of complex carbohydrates/fibers. * **Sucrose (D):** Sucrose is a disaccharide (table sugar) that is normally digested by sucrase in the small intestine. It is a substrate for metabolism, not a product of fiber fermentation. **Clinical Pearls for NEET-PG:** * **SCFA Ratio:** The typical molar ratio of Acetate:Propionate:Butyrate produced in the colon is approximately **60:20:20**. * **Systemic Effects:** While butyrate is used locally, **Acetate** enters the peripheral circulation and is used by peripheral tissues (muscle/brain), and **Propionate** is primarily taken up by the liver for gluconeogenesis. * **Health Benefit:** High-fiber diets are linked to a lower risk of colon cancer, largely due to the protective effects of butyrate on the colonic mucosa.

Question 190: Zinc deficiency is characterized by which of the following manifestations?

A. All of the below (Correct Answer)
B. Poor growth
C. Poor wound healing
D. Sexual infantilism

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**. Because it plays a fundamental role in protein synthesis, cell division, and nucleic acid metabolism, its deficiency affects multiple organ systems. **Explanation of Manifestations:** * **Poor Growth:** Zinc is vital for the synthesis of growth hormone and somatomedin-C. Deficiency leads to growth retardation and stunted skeletal development. * **Poor Wound Healing:** Zinc is required for collagen synthesis and fibroblast proliferation. It also plays a role in the inflammatory response and epithelialization; hence, deficiency significantly delays healing. * **Sexual Infantilism:** Zinc is crucial for the development of primary and secondary sexual characteristics. It is involved in testosterone synthesis and spermatogenesis. Deficiency leads to hypogonadism and delayed puberty. **Why "All of the below" is correct:** Since Zinc is ubiquitous in metabolic processes, its deficiency presents as a syndrome involving all the listed features, along with alopecia, dermatitis, and impaired taste (hypogeusia). **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder caused by a mutation in the **SLC39A4 gene**, leading to impaired zinc absorption. It presents with the triad of alopecia, diarrhea, and periorificial/acral dermatitis. * **Immunity:** Zinc deficiency causes thymic atrophy and impaired T-cell function, leading to increased susceptibility to infections. * **Diagnosis:** Serum zinc levels <70 µg/dL (though clinical response to supplementation is the gold standard).

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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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