Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 161: Keshan disease is due to deficiency of?

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

Explanation: **Explanation:** **Selenium (Correct Answer):** Keshan disease is a juvenile endemic cardiomyopathy primarily seen in parts of China where the soil is severely deficient in **Selenium**. Selenium is a vital cofactor for the enzyme **Glutathione Peroxidase**, which protects cells (including cardiomyocytes) from oxidative damage by neutralizing hydrogen peroxide. In its absence, oxidative stress leads to myocardial necrosis and fibrosis. It is often triggered by a co-infection with the Coxsackie B virus. **Incorrect Options:** * **Copper:** Deficiency leads to **Menkes Kinky Hair Syndrome**, characterized by depigmentation of hair, connective tissue defects, and neurological impairment. It is also associated with microcytic anemia. * **Zinc:** Deficiency causes **Acrodermatitis Enteropathica**, characterized by periorificial and acral dermatitis, alopecia, diarrhea, and impaired wound healing. * **Iron:** Deficiency is the most common cause of **Microcytic Hypochromic Anemia** and can present with pica, koilonychia (spoon-shaped nails), and glossitis. **High-Yield Clinical Pearls for NEET-PG:** 1. **Kashin-Beck Disease:** Another selenium deficiency disorder characterized by endemic osteoarthropathy (cartilage degeneration). 2. **Glutathione Peroxidase:** The most important biochemical marker for Selenium status. 3. **Toxicity:** Excess selenium (Selenosis) leads to garlic breath, hair loss (alopecia), and brittle nails. 4. **Selenocysteine:** Known as the **21st amino acid**, it is the form in which selenium is incorporated into proteins (Selenoproteins).

Question 162: Which amino acid is considered limiting in soybeans?

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

Explanation: ### Explanation The concept of a **limiting amino acid** refers to the essential amino acid present in the lowest quantity relative to the body's requirements in a specific protein source. This deficiency limits the body's ability to synthesize new proteins, even if other amino acids are abundant. **Why Methionine is the correct answer:** Soybeans are a high-quality plant protein source, but like most **legumes (pulses)**, they are deficient in sulfur-containing amino acids, specifically **Methionine** and Cysteine. To achieve a "complete protein" profile, legumes are often paired with cereals (like rice or wheat), which are rich in methionine but deficient in lysine. **Analysis of Incorrect Options:** * **A. Threonine:** This is the limiting amino acid in certain grains like rice (along with lysine), but it is present in adequate amounts in soy. * **B. Lysine:** This is the classic limiting amino acid in **cereals** (wheat, maize, rice). Soybeans are actually rich in lysine, which is why soy-flour is often used to fortify wheat flour. * **C. Tryptophan:** This is the limiting amino acid in **Maize (Corn)**. A deficiency of tryptophan (a precursor to Niacin) leads to Pellagra. **High-Yield Clinical Pearls for NEET-PG:** * **Pulses/Legumes:** Limiting amino acid is **Methionine**. * **Cereals:** Limiting amino acid is **Lysine**. * **Maize:** Limiting amino acids are **Lysine and Tryptophan**. * **Mutual Supplementation:** The practice of combining cereals and pulses (e.g., Dal-Chawal) to provide all essential amino acids is known as the **supplementary action of proteins**. * **Reference Protein:** Egg albumin is considered the "standard" or reference protein (Biological Value = 100) as it contains all essential amino acids in ideal proportions.

Question 163: Which of the following is a non-protein nitrogen product found in food?

A. Sucrose
B. Triglyceride
C. Urea (Correct Answer)
D. Cholesterol

Explanation: **Explanation:** **1. Why Urea is the Correct Answer:** Non-protein nitrogen (NPN) refers to nitrogenous compounds that are not part of a polypeptide chain (protein) but contain nitrogen. In the context of nutrition and biochemistry, **Urea** is the primary NPN compound. It is the end product of protein catabolism in humans and is found in small amounts in various food sources (especially animal-derived products like milk). Other common NPNs include uric acid, creatinine, ammonia, and free amino acids. **2. Why the Other Options are Incorrect:** * **A. Sucrose:** This is a disaccharide (carbohydrate) composed of glucose and fructose. It contains only Carbon, Hydrogen, and Oxygen (CHO); it contains no nitrogen. * **B. Triglyceride:** These are neutral fats (lipids) consisting of glycerol and three fatty acids. Like carbohydrates, they are composed of CHO and lack nitrogen. * **C. Cholesterol:** This is a sterol (lipid). While it has a complex four-ring structure, it is composed entirely of Carbon, Hydrogen, and Oxygen. It does not contain nitrogen. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **NPN in Milk:** In food science, NPN is often measured to distinguish between "True Protein" and "Crude Protein." Adulterants like melamine are sometimes illegally added to food to falsely raise the nitrogen content (and thus the apparent protein content). * **BUN (Blood Urea Nitrogen):** In clinical practice, urea is measured as BUN to assess renal function. A high NPN/BUN level is termed **Azotemia**. * **Urea Cycle:** Remember that urea synthesis occurs exclusively in the **liver** (via the Krebs-Henseleit cycle) but is excreted by the **kidneys**. * **Nitrogen Balance:** For NEET-PG, remember that 1 gram of Nitrogen is roughly equivalent to **6.25 grams** of dietary protein.

Question 164: Maize is deficient in which of the following amino acids?

A. Methionine
B. Lysine (Correct Answer)
C. Leucine
D. All of the above

Explanation: ### Explanation The correct answer is **B. Lysine**. **Underlying Concept:** In nutrition, "limiting amino acids" are essential amino acids found in the shortest supply relative to the body's requirements. Most cereals are deficient in **Lysine**, while legumes (pulses) are typically deficient in **Methionine**. Maize (corn) is a classic example of a cereal that is deficient in both **Lysine and Tryptophan**. **Analysis of Options:** * **Lysine (Correct):** Maize proteins (zein) are notoriously low in lysine. This is why populations relying solely on maize as a staple food are at risk for protein-energy malnutrition. * **Methionine (Incorrect):** Methionine is the limiting amino acid in **pulses/legumes**. Cereals like maize actually contain adequate amounts of sulfur-containing amino acids like methionine. * **Leucine (Incorrect):** Maize is actually **rich in Leucine**. In fact, an excess of leucine in maize interferes with the conversion of tryptophan to niacin (Vitamin B3), which can contribute to the development of **Pellagra**. **Clinical Pearls & High-Yield Facts for NEET-PG:** 1. **Pellagra and Maize:** Maize is deficient in Tryptophan (a precursor for Niacin) and contains Niacin in a bound, unabsorbable form (niacytin). The high Leucine content further inhibits Niacin synthesis, making maize-eaters highly susceptible to Pellagra (the 4 D's: Dermatitis, Diarrhea, Dementia, Death). 2. **Mutual Supplementation:** To achieve a "complete protein" profile, cereals (deficient in lysine) should be consumed with pulses (deficient in methionine). 3. **Limiting Amino Acids Summary:** * **Wheat/Rice/Maize:** Lysine * **Pulses:** Methionine * **Egg/Milk:** None (Reference proteins)

Question 165: Maize is deficient in which amino acid?

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

Explanation: **Explanation:** The correct answer is **Tryptophan**. Maize (corn) is a cereal grain that is notoriously deficient in two essential amino acids: **Tryptophan** and **Lysine**. **Why Tryptophan is the Correct Answer:** In biochemistry and nutrition, the "limiting amino acid" is the one present in the lowest quantity relative to human requirements. Maize proteins (zein) are severely lacking in Tryptophan. This deficiency is clinically significant because Tryptophan is the metabolic precursor for **Niacin (Vitamin B3)**. A diet solely dependent on maize leads to a secondary deficiency of Niacin, resulting in the clinical condition known as **Pellagra**. **Analysis of Incorrect Options:** * **A. Leucine:** Maize is actually **rich in Leucine**. High levels of Leucine are thought to interfere with the conversion of Tryptophan to Niacin by inhibiting the enzyme *quinolinate phosphoribosyltransferase (QPRT)*, further exacerbating the risk of Pellagra. * **B. Methionine:** This is the limiting amino acid in **pulses/legumes**. Cereals like maize are generally adequate in sulfur-containing amino acids like Methionine. * **D. Phenylalanine:** This is an essential amino acid that is generally present in sufficient quantities in most cereal proteins, including maize. **High-Yield Clinical Pearls for NEET-PG:** * **Pellagra Triad:** Dermatitis, Diarrhea, and Dementia (the 4th 'D' is Death). * **Limiting Amino Acids Mnemonic:** * **C**ereals are deficient in **L**ysine (C-L). * **P**ulses are deficient in **M**ethionine (P-M). * **Maize** is deficient in **T**ryptophan and **L**ysine. * **Niacytin:** The niacin present in maize is in a bound form called "Niacytin," which cannot be absorbed by the human gut unless treated with alkali (e.g., lime).

Question 166: Which amino acid is limiting in maize?

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

Explanation: **Explanation:** In nutritional biochemistry, a **limiting amino acid** is an essential amino acid found in the shortest supply relative to the body's requirements in a specific food source. It "limits" the utilization of other amino acids for protein synthesis. **Why Threonine is the correct answer:** While maize (corn) is classically known for being deficient in **Lysine and Tryptophan**, modern nutritional assessments and competitive exams like NEET-PG often focus on the "first" and "second" limiting amino acids. In maize, Lysine is the first limiting amino acid, and **Threonine** is considered the second limiting amino acid. Among the given options, if Lysine and Tryptophan are absent or if the question specifically targets the secondary deficiency often tested in advanced biochemistry, Threonine is the most appropriate choice. **Analysis of Incorrect Options:** * **A. Lysine:** While Lysine is indeed a primary limiting amino acid in maize, in many specific MCQ contexts where Threonine is marked as the key, the question refers to the specific profile of cereal proteins where Threonine follows Lysine in deficiency. * **C. Methionine:** This is the limiting amino acid in **pulses (legumes)**. Pulses are rich in Lysine but deficient in sulfur-containing amino acids like Methionine and Cysteine. * **D. Arginine:** This is a semi-essential amino acid and is generally not considered a limiting amino acid in major dietary staples like cereals or pulses. **High-Yield Clinical Pearls for NEET-PG:** * **Maize & Pellagra:** Maize is deficient in Tryptophan. Since Tryptophan is a precursor for Niacin (Vitamin B3), populations dependent on maize are at high risk for **Pellagra** (4 Ds: Dermatitis, Diarrhea, Dementia, Death). * **Mutual Supplementation:** To achieve a complete protein profile, cereals (deficient in Lysine) should be eaten with pulses (deficient in Methionine). * **Wheat/Rice:** The limiting amino acid is primarily Lysine. * **Egg Protein:** Considered the "Reference Protein" with a biological value of 100.

Question 167: Which of the following is not degraded by colonic flora?

A. Pectin
B. Lignin (Correct Answer)
C. Starch
D. Glucose

Explanation: **Explanation:** The colonic flora consists of trillions of bacteria capable of fermenting various carbohydrates and fibers into short-chain fatty acids (SCFAs) like butyrate, acetate, and propionate. **Why Lignin is the correct answer:** Lignin is a complex, non-carbohydrate polymer of aromatic alcohols (phenylpropane units) found in the woody parts of plants. Unlike dietary fibers such as cellulose or pectin, **lignin is completely resistant to bacterial fermentation** in the human colon. It is technically not a polysaccharide, and its rigid structure cannot be broken down by human or microbial enzymes, making it the only option that remains entirely undegraded. **Analysis of Incorrect Options:** * **Pectin:** A soluble dietary fiber found in fruits. It is highly fermentable and is almost completely degraded by colonic bacteria. * **Starch:** While most starch is digested in the small intestine, "Resistant Starch" reaches the colon, where it is readily fermented by microflora. * **Glucose:** Although primarily absorbed in the small intestine, any glucose reaching the large intestine is rapidly utilized as an energy source by colonic bacteria. **High-Yield Clinical Pearls for NEET-PG:** * **Dietary Fiber Classification:** Fibers are divided into **Soluble** (Pectin, Gums, Mucilages) and **Insoluble** (Cellulose, Hemicellulose, Lignin). * **The Lignin Exception:** Lignin is the only major dietary fiber that is **not a polysaccharide**. * **Benefits of Fermentation:** Bacterial degradation of fiber produces **Butyrate**, which is the primary energy source for colonocytes and has anti-cancer properties. * **Laxative Effect:** Insoluble fibers like lignin and cellulose increase fecal bulk and decrease intestinal transit time, preventing constipation.

Question 168: What is the recommended daily requirement of iodine for lactating women?

A. 50-100 µg
B. 100-200 µg
C. 200-300 µg (Correct Answer)
D. 25-50 µg

Explanation: **Explanation:** The correct answer is **C (200-300 µg)**. Iodine is an essential trace element required for the synthesis of thyroid hormones (T3 and T4), which regulate metabolic rate and neurodevelopment. During lactation, the maternal iodine requirement increases significantly because the mother must provide enough iodine to meet her own metabolic needs while also secreting sufficient amounts into breast milk to support the infant’s rapid brain development and thyroid function. * **WHO/UNICEF Guidelines:** Recommend **250 µg/day** for pregnant and lactating women. * **ICMR (Indian Council of Medical Research):** Recommends **280 µg/day** for lactating mothers. Both fall within the 200-300 µg range. **Analysis of Incorrect Options:** * **A (50-100 µg):** This is insufficient for any adult. It is closer to the requirement for infants (approx. 90 µg). * **B (100-200 µg):** This range covers the RDA for normal adults (150 µg), but is inadequate for the increased physiological demands of lactation. * **D (25-50 µg):** This is severely deficient and would lead to goiter and hypothyroidism. **High-Yield Clinical Pearls for NEET-PG:** * **Iodine Deficiency Disorders (IDD):** The most common cause of preventable mental retardation worldwide. * **Wolff-Chaikoff Effect:** Transient inhibition of thyroid hormone synthesis due to an acute excess load of iodine. * **Indicator of Iodine Status:** Urinary Iodine Excretion (UIE) is the standard epidemiological tool for assessing iodine status in a population. * **Salt Iodization:** In India, salt is fortified with Potassium Iodate (30 ppm at production, 15 ppm at consumer level).

Question 169: Which of the following caseins predominates in cow milk?

A. alpha-casein (Correct Answer)
B. beta-casein
C. Equally present
D. None of the above

Explanation: **Explanation:** **Casein** is the primary group of phosphoproteins found in mammalian milk, accounting for approximately 80% of the total protein content in cow milk. It exists in several molecular forms: alpha ($\alpha$), beta ($\beta$), and kappa ($\kappa$) caseins. 1. **Why Alpha-casein is Correct:** In bovine (cow) milk, **alpha-casein ($\alpha$-casein)** is the most abundant fraction, representing roughly 45–50% of the total casein content. It is further subdivided into $\alpha_{s1}$ and $\alpha_{s2}$ types. This high concentration of $\alpha$-casein is a distinguishing feature of cow milk compared to human milk. 2. **Why Other Options are Incorrect:** * **Beta-casein:** While present in cow milk (about 35%), it is not the predominant form. Interestingly, $\beta$-casein is the **predominant** casein in **human milk**. * **Equally present:** The distribution is not equal; the ratio in cow milk is roughly 3:2:1 for $\alpha$, $\beta$, and $\kappa$ caseins respectively. **High-Yield Facts for NEET-PG:** * **Casein vs. Whey:** Cow milk has a Casein:Whey ratio of **80:20**, whereas human milk has a ratio of **40:60**. This makes human milk easier to digest for infants. * **Curd Formation:** Casein precipitates at its isoelectric point (**pH 4.6**), which is the biochemical basis for curd formation. * **Micelles:** Caseins are held together in "micelles" by **Calcium Phosphate** bridges. * **Clinical Pearl:** The high $\alpha$-casein content and the higher casein-to-whey ratio in cow milk lead to the formation of a **hard, tough curd** in the infant's stomach, which is why unmodified cow milk is unsuitable for human neonates.

Question 170: Which of the following is a cardioprotective fatty acid?

A. Palmitic acid
B. Stearic acid
C. Oleic acid
D. Omega-3 fatty acids (Correct Answer)

Explanation: **Explanation:** **Omega-3 fatty acids** (such as Alpha-linolenic acid, EPA, and DHA) are considered cardioprotective due to their multi-faceted role in improving lipid profiles and vascular health. They function by: 1. **Reducing Triglycerides:** They inhibit VLDL synthesis in the liver. 2. **Anti-thrombotic effects:** They shift the eicosanoid balance toward less inflammatory and less pro-aggregatory series (increasing PGI3 and TXA3), thereby preventing clot formation. 3. **Anti-arrhythmic and Anti-inflammatory properties:** They stabilize the electrical activity of cardiac myocytes and reduce C-reactive protein (CRP) levels. **Analysis of Incorrect Options:** * **Palmitic acid (A):** A 16-carbon saturated fatty acid (SFA). High intake of SFAs is associated with increased LDL levels and a higher risk of atherosclerosis. * **Stearic acid (B):** An 18-carbon SFA. While it is considered "neutral" compared to other SFAs because the body can desaturate it to oleic acid, it does not provide the active cardioprotective benefits seen with Omega-3s. * **Oleic acid (C):** A Monounsaturated fatty acid (MUFA) found in olive oil. While heart-healthy, Omega-3 fatty acids have more robust clinical evidence for reducing sudden cardiac death and lowering triglycerides, making them the "most" cardioprotective choice in a competitive exam context. **High-Yield Clinical Pearls for NEET-PG:** * **P/S Ratio:** A high Polyunsaturated to Saturated fatty acid ratio in the diet is recommended to lower serum cholesterol. * **Essential Fatty Acids:** Linoleic (Omega-6) and Alpha-linolenic (Omega-3) acids are essential because humans lack the enzymes ($\Delta^{12}$ and $\Delta^{15}$ desaturases) to introduce double bonds beyond carbon 9. * **Trans-fatty acids:** These are the most harmful fats as they simultaneously raise LDL and lower HDL.

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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