Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 121: Which of the following best assesses protein quality?

A. Net protein utilization (Correct Answer)
B. Protein biological value
C. Digestibility coefficient
D. Protein energy ratio

Explanation: **Explanation:** Protein quality assessment is a critical concept in nutrition, focusing on how effectively dietary protein can be used for growth and maintenance. **Why Net Protein Utilization (NPU) is the correct answer:** NPU is considered the **best index** for assessing protein quality because it accounts for both **digestibility** and the **biological value** of the protein. It measures the proportion of dietary nitrogen that is actually retained by the body. * **Formula:** $NPU = \frac{\text{Nitrogen Retained}}{\text{Nitrogen Intake}} \times 100$ * Since it factors in how much protein is absorbed (digestibility) and how much of that absorbed protein is utilized (biological value), it provides the most accurate practical assessment of a protein's nutritional value. **Analysis of Incorrect Options:** * **B. Biological Value (BV):** This measures the percentage of *absorbed* nitrogen that is retained. It does not account for nitrogen lost in feces (digestibility). A protein could have a high BV but be poorly absorbed, making BV less comprehensive than NPU. * **C. Digestibility Coefficient:** This only measures the percentage of ingested nitrogen that is absorbed into the bloodstream. It tells us nothing about how well the body utilizes the protein once it is inside. * **D. Protein Energy Ratio:** This is a measure of the protein content of a diet relative to its total caloric value, used to assess the risk of protein-energy malnutrition (PEM), rather than the intrinsic quality of the protein itself. **High-Yield Clinical Pearls for NEET-PG:** * **Reference Protein:** Egg protein is considered the "standard" or "reference protein" with an NPU and BV of approximately 100. * **Limiting Amino Acids:** Pulses are deficient in **Methionine**, while Cereals are deficient in **Lysine**. * **PDCAAS:** The Protein Digestibility Corrected Amino Acid Score (PDCAAS) is currently the internationally accepted standard for evaluating protein quality in human nutrition.

Question 122: All are diagnostic features of osteomalacia except?

A. Increased serum calcium (Correct Answer)
B. Increased alkaline phosphatase
C. Proximal myopathy
D. Looser's zone

Explanation: **Explanation:** Osteomalacia is characterized by impaired mineralization of the bone matrix (osteoid) in adults, most commonly due to **Vitamin D deficiency**. **1. Why "Increased serum calcium" is the correct answer:** In osteomalacia, serum calcium is typically **low or low-normal**, never increased. Vitamin D deficiency leads to decreased intestinal absorption of calcium. This triggers secondary hyperparathyroidism (increased PTH) to maintain calcium levels by mobilizing it from bones, but the net result is still a state of calcium deficit. Hypercalcemia would point toward primary hyperparathyroidism or malignancy, not osteomalacia. **2. Analysis of other options:** * **Increased alkaline phosphatase (ALP):** This is a classic finding. Increased osteoblastic activity (an attempt to form new bone) results in elevated serum ALP levels. * **Proximal myopathy:** Vitamin D is essential for muscle function. Deficiency leads to "waddling gait" and proximal muscle weakness, a hallmark clinical feature of osteomalacia. * **Looser’s zones:** Also known as pseudofractures or Milkman’s lines, these are radiolucent bands representing unmineralized osteoid at sites of stress (e.g., femoral neck, ribs). They are **pathognomonic** for osteomalacia. **3. NEET-PG High-Yield Pearls:** * **Biochemical Profile:** ↓/Normal Calcium, ↓ Phosphate (due to PTH-induced renal wasting), ↑ PTH, and ↑ ALP. * **Radiology:** Look for "Codfish vertebrae" (biconcave) and Looser's zones. * **Histology:** The gold standard (though rarely done) shows an **increased thickness of osteoid seams**. * **Rickets vs. Osteomalacia:** Rickets occurs before epiphyseal closure (children); Osteomalacia occurs after (adults).

Question 123: Which of the following is NOT an antioxidant?

A. Carotenoids
B. Benzene (Correct Answer)
C. Vitamin E
D. Selenium

Explanation: **Explanation:** The correct answer is **Benzene**. An antioxidant is a molecule capable of inhibiting the oxidation of other molecules, thereby preventing the formation of free radicals and oxidative stress. **Why Benzene is the correct answer:** Benzene is a known **pro-oxidant** and a potent carcinogen. Its metabolism in the liver (via Cytochrome P450 2E1) generates reactive oxygen species (ROS) and toxic metabolites like hydroquinone and benzoquinone. Instead of neutralizing free radicals, benzene exposure leads to oxidative DNA damage and bone marrow toxicity (aplastic anemia and leukemia). **Why the other options are incorrect:** * **Carotenoids (Vitamin A precursors):** These are lipid-soluble antioxidants that quench singlet oxygen and neutralize lipid peroxyl radicals. They are vital for protecting cell membranes. * **Vitamin E (Tocopherol):** Known as the "most powerful chain-breaking antioxidant" in cell membranes. It prevents the peroxidation of polyunsaturated fatty acids (PUFAs). * **Selenium:** This is an essential trace element that acts as a co-factor for **Glutathione Peroxidase**, an enzyme that converts hydrogen peroxide into water, protecting the cell from oxidative damage. **High-Yield Clinical Pearls for NEET-PG:** * **Antioxidant Vitamins:** A, C, and E (ACE). * **Antioxidant Minerals:** Selenium, Zinc, Copper, and Manganese (often acting as enzyme co-factors). * **Glutathione:** The most abundant intracellular antioxidant. * **Superoxide Dismutase (SOD):** Converts superoxide radicals to $H_2O_2$; requires Copper/Zinc (cytosolic) or Manganese (mitochondrial).

Question 124: Cereals are deficient in which essential amino acid?

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

Explanation: **Explanation:** The nutritional quality of a protein is determined by its **limiting amino acid**—the essential amino acid present in the lowest amount relative to the body's requirements. **Why Lysine is correct:** Cereals (such as wheat, rice, and maize) are the primary source of carbohydrates globally but are nutritionally incomplete proteins. They are characteristically **deficient in Lysine**. Conversely, cereals are relatively rich in sulfur-containing amino acids like Methionine and Cysteine. This is why a vegetarian diet often combines cereals with pulses (which are rich in Lysine but deficient in Methionine) to achieve a "complementary protein" effect, ensuring a balanced intake of all essential amino acids. **Analysis of Incorrect Options:** * **Leucine:** This is a branched-chain amino acid (BCAA) found abundantly in most cereal grains. In fact, an excess of Leucine in Jowar (Sorghum) is linked to the inhibition of Tryptophan conversion to Niacin, potentially leading to Pellagra. * **Phenylalanine:** This is an aromatic amino acid generally present in adequate amounts in cereal proteins. * **Tryptophan:** While maize (corn) is specifically deficient in both Lysine and Tryptophan, for cereals as a general group, Lysine is the most universal limiting amino acid. **High-Yield Clinical Pearls for NEET-PG:** * **Pulses/Legumes:** Deficient in **Methionine** (but rich in Lysine). * **Maize:** Deficient in **Lysine and Tryptophan**. * **Reference Protein:** Egg albumin is considered the "standard" or reference protein (Biological Value = 100). * **Pellagra in Maize eaters:** Occurs because maize is low in Tryptophan (a precursor for Niacin) and its Niacin is in a bound, unabsorbable form (Niacytin).

Question 125: Which amino acid is deficient in pulses?

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

Explanation: **Explanation:** The nutritional quality of a protein is determined by its **limiting amino acid**—the essential amino acid present in the lowest amount relative to human requirements. In the context of plant-based nutrition, there is a classic "complementary" relationship between cereals and pulses. **Why Methionine is Correct:** Pulses (legumes) are an excellent source of lysine but are characteristically **deficient in sulfur-containing amino acids**, specifically **Methionine** and Cysteine. Therefore, methionine is the limiting amino acid in pulses. **Analysis of Incorrect Options:** * **B. Lysine:** This is the limiting amino acid in **Cereals** (wheat, rice, maize). Pulses are actually rich in lysine, which is why mixing cereals and pulses (e.g., Rice and Dal) provides a complete amino acid profile. * **C. Threonine:** This is the second limiting amino acid in many cereals (like wheat) but is generally adequate in pulses. * **D. Tryptophan:** This is the limiting amino acid in **Maize** (corn), along with lysine. A deficiency of tryptophan can lead to Pellagra because tryptophan is a precursor for Niacin (Vitamin B3) synthesis. **High-Yield NEET-PG Pearls:** 1. **Limiting Amino Acids Summary:** * **Pulses:** Methionine * **Cereals:** Lysine * **Maize:** Tryptophan and Lysine 2. **Reference Protein:** Egg protein (Albumin) is considered the "Gold Standard" or reference protein with a biological value of 100, as it contains all essential amino acids in ideal proportions. 3. **Mutual Supplementation:** The practice of combining pulses and cereals to compensate for each other's deficiencies is known as the "supplementary action of proteins."

Question 126: What is the daily required dose of iron in an adult man?

A. 0.7 mg
B. 0.8 mg
C. 0.9 mg (Correct Answer)
D. 1.0 mg

Explanation: **Explanation:** The daily iron requirement is determined by the amount of iron lost from the body that must be replaced through intestinal absorption. In an adult male, iron is lost primarily through the shedding of gastrointestinal mucosal cells, skin exfoliation, and trace amounts in urine and sweat. **1. Why 0.9 mg is correct:** According to the latest nutritional guidelines (including ICMR and WHO standards), the physiological requirement (the amount actually absorbed into the blood) for an adult male is approximately **0.9 mg/day**. While the *dietary intake* recommendation is higher (to account for low bioavailability), the actual physiological need to maintain iron balance in a healthy adult male is roughly 0.9 to 1.0 mg. In the context of standard medical examinations like NEET-PG, 0.9 mg is the most precise value cited for basal losses in males. **2. Analysis of Incorrect Options:** * **0.7 mg & 0.8 mg:** These values are too low to cover the average daily basal losses of a healthy adult male. * **1.0 mg:** While often used as a rounded figure in older textbooks, 0.9 mg is currently considered the more accurate physiological requirement. If 0.9 mg is an option, it is the preferred specific answer. **3. Clinical Pearls for NEET-PG:** * **Menstruating Women:** Require significantly more iron (**~1.6 mg/day**) due to monthly blood loss. * **Pregnancy:** Requirements spike to **~2.5 to 3.0 mg/day** (especially in the 2nd and 3rd trimesters). * **Absorption:** Only about **10%** of dietary iron is absorbed. Therefore, to meet a 0.9 mg physiological requirement, a man must consume roughly 9–10 mg of iron daily. * **Storage:** Iron is stored as **Ferritin** (labile) and **Hemosiderin** (insoluble). Ferritin levels are the most sensitive indicator of early iron deficiency.

Question 127: Keshan disease is characterized by cardiomegaly due to deficiency of which essential trace element?

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

Explanation: **Explanation:** **Selenium** is the correct answer because it is an essential component of the enzyme **Glutathione Peroxidase**, which protects cells from oxidative damage. **Keshan disease** is a juvenile cardiomyopathy characterized by cardiomegaly and heart failure, primarily seen in regions of China with selenium-deficient soil. While the deficiency is the primary cause, it is often triggered by a co-infection with the Coxsackievirus B. **Analysis of Incorrect Options:** * **B. Copper:** Deficiency leads to **Menkes Kinky Hair Syndrome** (pili torti, neurological issues) and microcytic anemia. Excess copper causes Wilson’s disease. * **C. Zinc:** Deficiency results in **Acrodermatitis enteropathica**, characterized by periorificial dermatitis, alopecia, diarrhea, and poor wound healing. * **D. Iron:** Deficiency is the most common cause of **Microcytic Hypochromic Anemia** and is associated with Pica and Plummer-Vinson syndrome. **High-Yield Clinical Pearls for NEET-PG:** * **Kashin-Beck Disease:** Another selenium deficiency disorder characterized by osteoarthropathy (degeneration of joint cartilage). * **Selenocysteine:** Known as the **21st amino acid**, it is the form in which selenium is incorporated into proteins (e.g., Deiodinase, which converts T4 to T3). * **Toxicity:** Excess selenium (Selenosis) leads to garlic breath, hair loss, and nail dystrophy. * **Glutathione Peroxidase:** Uses reduced glutathione to neutralize hydrogen peroxide ($H_2O_2$), protecting RBCs and cardiac tissue from oxidative stress.

Question 128: What is the recommended daily intake of dietary fiber?

A. 20 grams
B. 40 grams (Correct Answer)
C. 80 grams
D. 100 grams

Explanation: **Explanation:** The correct answer is **40 grams**. According to the Indian Council of Medical Research (ICMR) and the National Institute of Nutrition (NIN) guidelines, the recommended dietary allowance (RDA) for fiber is approximately **40 g/2000 kcal/day**. **Why 40 grams is correct:** Dietary fiber consists of non-starch polysaccharides (like cellulose, hemicellulose, and pectin) and lignin that are resistant to human digestive enzymes. A daily intake of 40g is recommended to maintain optimal gastrointestinal health, ensure adequate stool bulk, and provide metabolic benefits such as lowering glycemic index and reducing LDL cholesterol. **Why other options are incorrect:** * **20 grams:** While some international guidelines (like the AHA) suggest a minimum of 25–30g, 20g is considered insufficient for the high-carbohydrate Indian diet to effectively prevent lifestyle diseases. * **80 grams & 100 grams:** These values are excessively high. While high-fiber diets are beneficial, exceeding 50–60g/day can lead to malabsorption of essential micronutrients (like calcium, iron, and zinc) due to the presence of phytates and oxalates, and may cause significant abdominal bloating or intestinal obstruction. **High-Yield Clinical Pearls for NEET-PG:** * **Soluble Fiber (e.g., Pectin, Gums):** Delays gastric emptying and lowers blood cholesterol by binding bile acids. * **Insoluble Fiber (e.g., Cellulose, Lignin):** Increases stool bulk and decreases intestinal transit time; protective against colon cancer and diverticulosis. * **Caloric Value:** Fiber provides approximately **2 kcal/g** through the production of Short-Chain Fatty Acids (SCFAs) like butyrate by colonic bacteria. * **Crude Fiber vs. Dietary Fiber:** Dietary fiber values are usually 2–3 times higher than crude fiber values.

Question 129: Which of the following is the poorest source of calcium?

A. Rice (Correct Answer)
B. Human milk
C. Egg yolk
D. Cow's milk

Explanation: **Explanation:** The question tests the knowledge of dietary sources of calcium, a critical mineral for bone mineralization and cellular signaling. **1. Why Rice is the Correct Answer:** Cereals, particularly polished **rice**, are notoriously poor sources of calcium. Rice contains approximately **10 mg of calcium per 100 g**, which is significantly lower than animal-based sources or other millets (like Ragi). Furthermore, rice contains **phytates**, which act as anti-nutrients by binding to the small amount of calcium present, further reducing its bioavailability in the gut. **2. Analysis of Incorrect Options:** * **Cow’s Milk:** This is one of the richest and most bioavailable sources of calcium, containing about **120 mg/100 ml**. It is considered the gold standard for dietary calcium. * **Human Milk:** While it contains less calcium than cow’s milk (approx. **28–34 mg/100 ml**), it is still a superior source compared to rice. The calcium-to-phosphorus ratio in human milk is highly optimized for maximum absorption in infants. * **Egg Yolk:** Eggs are a good source of minerals. While the white is mostly protein (albumin), the yolk contains significant calcium (approx. **130 mg/100 g**), along with Vitamin D, which aids calcium absorption. **3. High-Yield Clinical Pearls for NEET-PG:** * **Best Source:** Among cereals/millets, **Ragi (Finger millet)** is the richest source of calcium (~344 mg/100 g). * **Absorption:** Calcium absorption requires **Vitamin D** (Calcitriol) and is inhibited by phytates (cereals), oxalates (spinach), and high dietary fiber. * **Hormonal Regulation:** Serum calcium levels are strictly maintained by **PTH** (increases calcium) and **Calcitonin** (decreases calcium). * **Daily Requirement:** An average adult requires approximately **600–1000 mg/day**, with increased needs during pregnancy and lactation (1200 mg/day).

Question 130: Soya bean is rich in which of the following amino acids?

A. Lysine (Correct Answer)
B. Aspartic acid
C. Glycine
D. Alanine

Explanation: **Explanation:** The nutritional quality of a protein is determined by its **essential amino acid (EAA)** profile. Most plant-based proteins are "incomplete" because they are deficient in one or more EAAs. However, **Soybean** is a unique exception in the plant kingdom as it contains all essential amino acids in sufficient quantities, making it a "complete protein." **1. Why Lysine is Correct:** Cereals (like wheat, rice, and maize) are notoriously deficient in **Lysine** but rich in methionine. Conversely, pulses and legumes (like soybeans) are rich in **Lysine** but deficient in methionine. This complementary relationship is the basis of "mutual supplementation" in vegetarian diets (e.g., eating dal with rice). Soybean stands out because it has the highest lysine content among common plant sources, often used to fortify cereal-based diets. **2. Why Other Options are Incorrect:** * **Aspartic acid, Glycine, and Alanine:** These are **non-essential amino acids**. The body can synthesize them endogenously. In the context of nutrition and NEET-PG questions, the focus is almost always on the "limiting" or "abundant" **essential** amino acids, as these dictate the biological value of the food. While soybean contains these amino acids, they do not define its unique nutritional importance. **High-Yield Clinical Pearls for NEET-PG:** * **Limiting Amino Acids:** * **Pulses:** Methionine (and Cysteine). * **Cereals:** Lysine (and Threonine). * **Maize:** Tryptophan and Lysine (leads to Pellagra-like symptoms if maize is the sole staple). * **Reference Protein:** Egg (Albumin) is considered the reference protein with a biological value of 100. * **Antinutritional Factor:** Raw soybeans contain **Trypsin inhibitors**, which must be inactivated by heat (cooking) to ensure proper protein digestion.

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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