Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 31: Which of the following is NOT an essential trace element?

A. Chromium
B. Molybdenum
C. Magnesium
D. Cesium (Correct Answer)

Explanation: **Explanation:** The classification of minerals in human nutrition is based on the daily requirement: **Macro-minerals** (>100 mg/day) and **Trace elements** (<100 mg/day). **Why Cesium is the correct answer:** **Cesium (Cs)** is a heavy metal that has no known physiological or biological role in human metabolism. While it can be found in trace amounts in the body due to environmental exposure, it is not required for any enzymatic or structural function, making it **non-essential**. **Analysis of incorrect options:** * **Chromium (Cr):** An essential trace element required for carbohydrate metabolism. It functions as a component of the **Glucose Tolerance Factor (GTF)**, which enhances the action of insulin. * **Molybdenum (Mo):** An essential trace element that acts as a cofactor for several important enzymes, including **Xanthine Oxidase** (purine catabolism) and Sulfite Oxidase. * **Magnesium (Mg):** While technically a **Macro-mineral** (required in amounts >100 mg/day), it is a vital biological element. In the context of this question, it is a recognized essential nutrient, unlike Cesium. **High-Yield NEET-PG Pearls:** 1. **Essential Trace Elements:** Include Iron, Iodine, Zinc, Copper, Manganese, Chromium, Cobalt, Selenium, and Molybdenum. 2. **Fluorine:** Often considered a "beneficial" trace element for dental health but its status as "essential" is debated. 3. **Selenium:** A vital component of the enzyme **Glutathione Peroxidase**, which protects cells from oxidative damage. 4. **Zinc:** Essential for over 300 enzymes (e.g., Carbonic Anhydrase, DNA polymerase) and "Zinc fingers" in DNA binding proteins.

Question 32: Generalized body edema is associated with a deficiency of which of the following substances?

A. Vitamin B12
B. Sodium
C. Albumin (Correct Answer)
D. Essential Fatty Acids (EFAs)

Explanation: **Explanation:** The correct answer is **Albumin**. **1. Why Albumin is Correct:** Albumin is the primary protein responsible for maintaining **Plasma Colloid Osmotic Pressure (COPs)**. According to Starling’s Law, this pressure acts as a "pulling force" that keeps fluid within the intravascular compartment. When albumin levels drop (hypoalbuminemia)—due to malnutrition (Kwashiorkor), liver failure (decreased synthesis), or nephrotic syndrome (increased loss)—the oncotic pressure decreases. This allows fluid to leak from the capillaries into the interstitial space, resulting in **generalized body edema (anasarca)**. **2. Why the Other Options are Incorrect:** * **Vitamin B12:** Deficiency primarily leads to Megaloblastic Anemia and neurological symptoms (Subacute Combined Degeneration of the Spinal Cord), not edema. * **Sodium:** While sodium is the major extracellular cation, its deficiency (hyponatremia) typically causes cellular swelling (especially in the brain) rather than generalized peripheral edema. In fact, sodium *excess* (retention) is more commonly associated with edema. * **Essential Fatty Acids (EFAs):** Deficiency (e.g., Linoleic acid) leads to phrynoderma (toad skin), poor wound healing, and hair loss, but does not directly cause generalized edema. **3. NEET-PG High-Yield Pearls:** * **Kwashiorkor vs. Marasmus:** Edema is the hallmark of **Kwashiorkor** (protein deficiency with adequate calories) due to hypoalbuminemia. It is absent in **Marasmus** (total calorie deficiency). * **Normal Albumin Levels:** 3.5 to 5.0 g/dL. Edema usually manifests when levels fall below **2.5 g/dL**. * **Synthesis:** Albumin is synthesized exclusively in the liver and has a half-life of approximately 20 days.

Question 33: Which of the following minerals cannot generate free radicals?

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

Explanation: **Explanation:** The generation of free radicals by minerals typically occurs via **redox cycling** (such as the Fenton and Haber-Weiss reactions). This process requires the metal to be a **transition element** capable of existing in multiple oxidation states and acting as a pro-oxidant. **Why Selenium is the Correct Answer:** Unlike the other options, **Selenium (Se)** is primarily an **antioxidant** mineral. It does not participate in redox cycling to generate free radicals; instead, it is a vital structural component of antioxidant enzymes like **Glutathione Peroxidase (GPx)** and **Thioredoxin Reductase**. These enzymes are responsible for neutralizing hydrogen peroxide and lipid hydroperoxides, thereby protecting the cell from oxidative stress. **Analysis of Incorrect Options:** * **Copper (A):** A potent pro-oxidant. It undergoes redox cycling ($Cu^+ \leftrightarrow Cu^{2+}$) to generate the highly reactive hydroxyl radical (•OH) via Fenton-like chemistry. * **Cobalt (C) & Nickel (D):** Both are transition metals that can catalyze the formation of Reactive Oxygen Species (ROS). They can deplete cellular glutathione and trigger lipid peroxidation, contributing to oxidative DNA damage. **Clinical Pearls for NEET-PG:** * **Fenton Reaction:** $Fe^{2+} + H_2O_2 \rightarrow Fe^{3+} + \cdot OH + OH^-$. (Copper can substitute for Iron). * **Selenium Deficiency:** Leads to **Keshan Disease** (cardiomyopathy) and **Kashin-Beck Disease** (osteoarthritis). * **Glutathione Peroxidase:** Requires **Selenocysteine** (the 21st amino acid) at its active site for its catalytic activity.

Question 34: Which of the following is not a source of lysine?

A. Wheat (Correct Answer)
B. Rice
C. Bengal gram
D. Red gram

Explanation: **Explanation:** The nutritional quality of a protein is determined by its **essential amino acid** profile. Most plant-based proteins are "incomplete" because they lack one or more essential amino acids, known as the **limiting amino acids**. **Why Wheat is the Correct Answer:** Cereals, including **wheat**, maize, and barley, are characteristically deficient in **Lysine**. While wheat contains small amounts of protein (gluten), lysine is its primary limiting amino acid. In the context of competitive exams like NEET-PG, when asked for a "non-source" or the "most deficient" source among cereals and pulses, wheat is the classic example of lysine deficiency. **Analysis of Other Options:** * **Rice:** Like wheat, rice is a cereal and is also deficient in lysine. However, in comparative nutritional biochemistry, rice protein (oryzenin) has a slightly better amino acid profile and higher biological value than wheat. In many MCQ formats, if both are present, wheat is the prioritized answer for lysine deficiency. * **Bengal Gram & Red Gram (Pulses):** Pulses and legumes are **rich sources of Lysine**. Their limiting amino acids are the sulfur-containing amino acids (Methionine and Cysteine). Therefore, they are not the correct answer for a lack of lysine. **Clinical Pearls for NEET-PG:** 1. **Mutual Supplementation:** To achieve a complete protein profile, cereals (deficient in lysine, rich in methionine) are consumed with pulses (rich in lysine, deficient in methionine). This is the biochemical basis for traditional diets like "Dal-Chawal" or "Roti-Dal." 2. **Limiting Amino Acids Summary:** * **Cereals (Wheat, Rice):** Lysine (Primary), Threonine. * **Pulses:** Methionine, Cysteine. * **Maize:** Lysine and Tryptophan (deficiency leads to Pellagra-like symptoms). 3. **Reference Protein:** Egg albumin is considered the "standard" or reference protein with a biological value of 100.

Question 35: All of the following are complications in a patient on total parenteral nutrition except:

A. Hypercholesterolemia
B. Hyperglycemia
C. Hypotriglyceridemia (Correct Answer)
D. Hypophosphatemia

Explanation: Total Parenteral Nutrition (TPN) is a life-saving intervention that bypasses the gastrointestinal tract, but it carries significant metabolic risks due to the direct infusion of concentrated nutrients into the systemic circulation. ### **Explanation of the Correct Answer** **C. Hypotriglyceridemia:** This is the correct answer because TPN typically causes **Hypertriglyceridemia**, not hypotriglyceridemia. TPN solutions contain lipid emulsions (Intralipid) to provide essential fatty acids and calories. Excessive lipid infusion or a decreased clearance rate (due to reduced lipoprotein lipase activity) often leads to elevated serum triglycerides. ### **Analysis of Incorrect Options** * **Hyperglycemia (B):** This is the most common metabolic complication of TPN. The high glucose load in the infusate, often combined with the stress response of the underlying illness, can overwhelm the body's insulin capacity. * **Hypophosphatemia (D):** This is a hallmark of **Refeeding Syndrome**. When glucose is infused, insulin is released, causing an intracellular shift of phosphate, magnesium, and potassium. This can lead to severe muscle weakness and cardiac arrhythmias. * **Hypercholesterolemia (A):** Prolonged TPN, especially those with high lipid content, can lead to elevations in serum cholesterol and TPN-associated liver disease (steatosis). ### **NEET-PG High-Yield Pearls** * **Refeeding Syndrome:** Characterized by "Low P, Low K, Low Mg" (Hypophosphatemia, Hypokalemia, Hypomagnesemia) and fluid retention. * **Most common infection:** *Staphylococcus aureus* and *Candida* (due to high glucose content in the central line). * **Hepatobiliary Complications:** Cholestasis and gallstones (cholelithiasis) occur because the lack of enteral feeding leads to gallbladder stasis. * **Essential Fatty Acid Deficiency (EFAD):** Can occur if lipid emulsions are omitted; presents with scaly dermatitis and alopecia.

Question 36: During the 3rd day to 2nd week of starvation, on which of the following substances does the brain primarily depend as fuel?

A. Ketone bodies (Correct Answer)
B. Glucose
C. Fatty acid
D. Amino acid

Explanation: ### Explanation The brain typically relies on glucose as its primary fuel. However, during prolonged starvation (beyond 48–72 hours), metabolic shifts occur to preserve muscle mass and maintain cerebral function. **Why Ketone Bodies are Correct:** By the 3rd day of starvation, liver glycogen stores are completely exhausted. To prevent the excessive breakdown of muscle protein for gluconeogenesis, the body ramps up **ketogenesis** in the liver. Free fatty acids are converted into **Acetoacetate** and **β-hydroxybutyrate**. These ketone bodies cross the blood-brain barrier and are oxidized by the brain. By the 2nd week, ketone bodies provide approximately **60–70%** of the brain's energy requirements, significantly reducing the brain's glucose demand. **Analysis of Incorrect Options:** * **B. Glucose:** While the brain always requires *some* glucose (for intermediates of the TCA cycle), its dependence drops from 100% to about 30% during prolonged starvation to spare body proteins. * **C. Fatty Acids:** Although the body has abundant fat stores, long-chain fatty acids **cannot cross the blood-brain barrier** and therefore cannot be used directly by the brain as fuel. * **D. Amino Acids:** These are used by the liver for gluconeogenesis (to supply glucose) but are not a direct primary fuel source for the brain. The switch to ketones is specifically designed to *spare* amino acids. **NEET-PG High-Yield Pearls:** * **Sequence of Fuel:** Glucose (Early) → Ketone Bodies (Starvation) → Amino acids/Proteins (Final/Pre-terminal stage). * **Key Enzyme:** The brain can use ketones because it expresses **Thiophorase** (Succinyl-CoA:3-ketoacid CoA transferase), an enzyme **absent in the liver** (preventing the liver from consuming the ketones it produces). * **Gluconeogenesis Shift:** During early starvation, the liver is the primary site; in late starvation, the **kidney** contributes up to 40% of gluconeogenesis.

Question 37: Which of the following has the highest protein energy ratio?

A. Milk
B. Pulses
C. Potato
D. Fish (Correct Answer)

Explanation: **Explanation:** The **Protein-Energy Ratio (PE Ratio)** is a measure of the proportion of total energy (calories) in a food item that is derived from its protein content. It is calculated as: *(Energy from Protein / Total Energy) × 100*. **1. Why Fish is the Correct Answer:** Fish is considered a "lean" source of high-quality protein. It contains very little carbohydrate and, depending on the species, low to moderate fat. Consequently, a vast majority of its caloric value comes from protein. In most varieties of fish, the PE ratio exceeds **25-30%**, which is significantly higher than most plant-based or dairy sources. **2. Analysis of Incorrect Options:** * **Milk (A):** While milk is a complete protein source, it contains significant amounts of lactose (carbohydrate) and lipids. Its PE ratio is approximately **20%**. * **Pulses (B):** Pulses are rich in protein (approx. 20-25% by weight), but they also contain a very high percentage of complex carbohydrates (starch). This lowers their PE ratio to roughly **12-15%**. * **Potato (C):** Potato is primarily a starchy vegetable. While it contains high-quality protein (tuberin), the quantity is very low (approx. 2%). Its PE ratio is only about **5-6%**. **High-Yield Clinical Pearls for NEET-PG:** * **Reference Protein:** Egg is considered the reference protein (Biological Value = 100) due to its ideal amino acid profile. * **Limiting Amino Acids:** Pulses are deficient in **Methionine**, while Cereals are deficient in **Lysine**. * **Net Protein Utilization (NPU):** Highest for Egg (94), followed by Milk (75-80), Fish (75), and Meat (70). * **Kwashiorkor vs. Marasmus:** Kwashiorkor is primarily a deficiency of protein (low PE ratio diet), whereas Marasmus is a deficiency of total calories (Energy).

Question 38: Fatty liver in Kwashiorkor occurs due to what?

A. High carbohydrate content in the diet
B. High fat content in the diet
C. Lack of substrates for protein synthesis in the liver (Correct Answer)
D. Lack of substrates for gluconeogenesis in the liver

Explanation: ### Explanation **Correct Answer: C. Lack of substrates for protein synthesis in the liver** The hallmark of **Kwashiorkor** is a severe deficiency of dietary protein despite adequate caloric intake. The development of fatty liver (steatosis) in these patients is primarily due to the **impaired synthesis of Apolipoprotein B-100**. In a healthy state, the liver exports excess triglycerides into the systemic circulation in the form of **Very Low-Density Lipoproteins (VLDL)**. The assembly of VLDL requires both lipids and a protein component, specifically Apo B-100. In Kwashiorkor, the lack of essential amino acids (substrates) prevents the liver from synthesizing these apolipoproteins. Consequently, triglycerides cannot be packaged into VLDL and exported, leading to their accumulation within the hepatocytes, resulting in an enlarged, fatty liver. #### Analysis of Incorrect Options: * **A & B (High carbohydrate/fat content):** While Kwashiorkor diets are often high in carbohydrates (e.g., maize or rice), the fatty liver is not caused by the *excess* of these macronutrients, but rather by the *inability to transport* fat out of the liver due to protein deficiency. * **D (Lack of substrates for gluconeogenesis):** While gluconeogenesis may be affected in malnutrition, it is not the mechanism behind lipid accumulation. Fatty liver is a transport failure, not a glucose production failure. #### NEET-PG High-Yield Pearls: * **Kwashiorkor vs. Marasmus:** Kwashiorkor presents with **edema** (due to hypoalbuminemia) and fatty liver; Marasmus presents with "skin and bones" appearance and no edema. * **Key Clinical Signs:** "Flaky paint" dermatosis and "Flag sign" (alternating bands of hair color). * **VLDL Assembly:** Remember that **Apo B-100** is essential for VLDL (liver), while **Apo B-48** is essential for Chylomicrons (intestine). A defect in both leads to Abetalipoproteinemia.

Question 39: Which of the following has antioxidant properties?

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

Explanation: **Explanation:** The correct answer is **All of the above** because Selenium, Copper, and Zinc are essential trace minerals that function as integral cofactors for key antioxidant enzymes in the body. These enzymes neutralize reactive oxygen species (ROS), protecting cells from oxidative stress. 1. **Selenium (Se):** It is a vital component of **Glutathione Peroxidase (GPx)**, an enzyme that converts hydrogen peroxide into water, preventing lipid peroxidation. It is also found in Thioredoxin reductase. 2. **Copper (Cu) and Zinc (Zn):** Both are essential cofactors for the cytosolic enzyme **Superoxide Dismutase (Cu-Zn SOD)**. This enzyme catalyzes the dismutation of the highly reactive superoxide radical ($O_2^-$) into oxygen and hydrogen peroxide. * *Note:* Manganese (Mn) is the cofactor for mitochondrial SOD. **Why other options are not "wrong":** In this "All of the above" format, each individual mineral contributes to the antioxidant defense system. While they are not antioxidants themselves in their elemental form, their biological roles as **metalloenzymes** make them indispensable for antioxidant activity. **High-Yield Clinical Pearls for NEET-PG:** * **Selenium Deficiency:** Linked to **Keshan disease** (endemic cardiomyopathy). * **Zinc Deficiency:** Characterized by **Acrodermatitis enteropathica**, poor wound healing, and hypogeusia (decreased taste). * **Vitamin Synergy:** Vitamin E and Selenium act synergistically; Vitamin E prevents the formation of hydroperoxides, while Selenium (via GPx) destroys them. * **Other Antioxidants:** Remember the mnemonic **"ACES"** (Vitamins A, C, E, and Selenium).

Question 40: Which of the following proteins is biologically complete?

A. Egg
B. Milk
C. Both egg and milk (Correct Answer)
D. None of the above

Explanation: ### Explanation **Concept: Biological Value and Complete Proteins** A **biologically complete protein** (or high-quality protein) is one that contains all the **essential amino acids** (EAAs) in the correct proportions required for human growth and maintenance. These proteins typically have a high **Biological Value (BV)** and a high **Net Protein Utilization (NPU)**. **Why "Both Egg and Milk" is Correct:** * **Egg Protein:** Often referred to as the "Reference Protein," egg albumin contains all essential amino acids with a Biological Value of **100**. It is the gold standard against which all other dietary proteins are measured. * **Milk Protein:** Casein and whey proteins in milk are also complete proteins. They provide a balanced profile of all EAAs necessary for infants and adults, with a high BV (approx. 85–90). Since both sources provide the full spectrum of essential amino acids, Option C is the most accurate choice. **Analysis of Incorrect Options:** * **Option A & B:** While both are complete proteins, selecting one over the other would be incomplete. In the context of NEET-PG, when two high-quality animal proteins are listed, the combined option is the standard answer. * **Option D:** This is incorrect because animal-derived proteins (except gelatin) are generally complete, unlike plant proteins which often lack specific amino acids (e.g., pulses lack methionine; cereals lack lysine). **High-Yield Clinical Pearls for NEET-PG:** * **Reference Protein:** Egg is the reference protein (BV = 100). * **Limiting Amino Acids:** * **Pulses:** Deficient in Methionine and Cysteine. * **Cereals:** Deficient in Lysine and Threonine. * **Maize:** Deficient in Tryptophan and Lysine (leads to Pellagra-like symptoms). * **Gelatin:** The only animal protein that is **incomplete** (lacks Tryptophan). * **Mutual Supplementation:** Combining cereals and pulses (e.g., Rice and Dal) compensates for each other's limiting amino acids, creating a complete protein profile.

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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