Nutrition and Metabolism — MCQs

An obese individual is brought to the emergency room by a concerned friend. The patient has been on a self-imposed "starvation diet" for four months, and has lost 60 pounds while consuming only water and vitamin pills. If extensive blood studies were performed, which of the following would be expected to be elevated?

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 131: Glutathione peroxidase contains which of the following trace elements?

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

Explanation: **Explanation:** The correct answer is **Selenium (D)**. **Why Selenium is Correct:** Glutathione peroxidase (GPx) is a vital antioxidant enzyme that protects cells from oxidative damage by reducing lipid hydroperoxides and free hydrogen peroxide ($H_2O_2$) into water. It requires **Selenium** as an essential cofactor. Specifically, Selenium is incorporated into the enzyme's active site in the form of **Selenocysteine**, often referred to as the "21st amino acid." This trace element is crucial for the enzyme's catalytic activity in neutralizing reactive oxygen species (ROS). **Why Other Options are Incorrect:** * **Chromium (A):** Primarily functions as a component of the **Glucose Tolerance Factor (GTF)**, which enhances the action of insulin. * **Manganese (B):** Acts as a cofactor for enzymes like **Superoxide Dismutase (Mn-SOD)** found in mitochondria, Arginase, and Pyruvate carboxylase. * **Zinc (C):** A cofactor for over 300 enzymes, including **Cytoplasmic SOD (Cu-Zn SOD)**, Carbonic anhydrase, Alcohol dehydrogenase, and DNA/RNA polymerases. **High-Yield Clinical Pearls for NEET-PG:** * **Keshan Disease:** A cardiomyopathy resulting from Selenium deficiency, often seen in regions with selenium-poor soil. * **Kashin-Beck Disease:** An osteoarthropathy associated with Selenium deficiency. * **Antioxidant Defense:** While Glutathione Peroxidase requires Selenium, remember that **Superoxide Dismutase (SOD)** requires Copper, Zinc, or Manganese, and **Catalase** requires Iron (Heme). * **Selenocysteine** is encoded by the stop codon **UGA**, requiring a specific insertion sequence (SECIS) in the mRNA.

Question 132: Which of the following has the maximum medium-chain fatty acid content?

A. Sunflower oil
B. Flaxseed oil
C. Coconut oil (Correct Answer)
D. Fish oil

Explanation: **Explanation:** The correct answer is **Coconut oil**. **1. Why Coconut Oil is Correct:** Medium-chain fatty acids (MCFAs) are fatty acids with a carbon chain length of 6 to 12 carbons (e.g., Caprylic and Lauric acid). **Coconut oil** is the richest natural source of MCFAs, containing approximately **60-65%** medium-chain triglycerides (MCTs). Unlike long-chain fatty acids, MCTs are unique because they are absorbed directly into the portal circulation without requiring bile salts or chylomicron formation, making them a vital energy source for patients with malabsorption syndromes. **2. Why the Other Options are Incorrect:** * **Sunflower oil:** Primarily composed of Long-Chain Fatty Acids (LCFAs), specifically Omega-6 polyunsaturated fatty acids (PUFA) like Linoleic acid. * **Flaxseed oil:** A major source of Alpha-linolenic acid (ALA), which is an essential Omega-3 polyunsaturated **long-chain** fatty acid. * **Fish oil:** Renowned for its high content of Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA). These are **very-long-chain** Omega-3 fatty acids (20-22 carbons). **3. High-Yield Clinical Pearls for NEET-PG:** * **Therapeutic Use:** MCTs are used in the dietary management of **Chyluria**, **Short Bowel Syndrome**, and **Pancreatic insufficiency** because they bypass the lymphatic system. * **Essential Fatty Acids:** Remember that Linoleic (ω-6) and Linolenic (ω-3) acids are "essential" because humans lack the enzymes (Δ12 and Δ15 desaturases) to introduce double bonds beyond carbon 9. * **Rancidity:** Oils with high PUFA content (like Sunflower) are more prone to oxidative rancidity compared to saturated-rich Coconut oil.

Question 133: Which of the following food items has the highest Glycemic Index?

A. Corn flakes (Correct Answer)
B. Brown rice
C. Ice-cream
D. Whole wheat bread

Explanation: **Explanation:** The **Glycemic Index (GI)** is a ranking of carbohydrates on a scale of 0 to 100 based on how quickly they raise blood glucose levels after consumption. Foods with a high GI (>70) are rapidly digested and absorbed, causing a sharp spike in blood sugar. **Why Corn Flakes is the correct answer:** Corn flakes undergo extensive industrial processing (extrusion and high-heat treatment), which gelatinizes the starch. This makes the starch highly accessible to digestive enzymes like alpha-amylase. Consequently, corn flakes have a very high GI (approximately **81–93**), leading to a rapid postprandial glucose surge. **Analysis of Incorrect Options:** * **Brown rice (GI ~50–55):** It is a whole grain that retains the bran and germ layer. The high fiber content slows down the enzymatic breakdown of starch, resulting in a low-to-medium GI. * **Ice-cream (GI ~50–60):** Despite the high sugar content, ice cream contains significant amounts of fat and sometimes protein. Fat delays gastric emptying, which slows the absorption of glucose into the bloodstream, resulting in a lower GI than many processed cereals. * **Whole wheat bread (GI ~71–75):** While considered "high" GI, it is generally lower than corn flakes. The presence of intact fiber and complex structures in whole wheat slightly moderates the glycemic response compared to highly processed corn grits. **High-Yield Clinical Pearls for NEET-PG:** * **Reference Standard:** The GI is usually measured against **Glucose or White Bread** (both assigned a value of 100). * **Glycemic Load (GL):** This is a more practical clinical measure as it accounts for both the GI and the actual portion size (GL = GI × Carbohydrate amount / 100). * **Clinical Utility:** Low GI diets are recommended in the management of **Diabetes Mellitus, PCOS, and Metabolic Syndrome** to improve insulin sensitivity and weight loss.

Question 134: Which of the following is not a trace element?

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

Explanation: **Explanation:** In medical biochemistry, minerals are classified based on their daily dietary requirement and their concentration in the body into two categories: **Macro-elements (Major minerals)** and **Trace elements (Micro-minerals).** **Why Calcium is the correct answer:** Calcium is a **Macro-element**. Macro-elements are required in the diet in amounts greater than **100 mg/day**. Calcium is the most abundant mineral in the human body (approx. 1–1.5 kg in an adult), essential for bone mineralization, blood coagulation, and neuromuscular signaling. Other macro-elements include Magnesium, Phosphorus, Sodium, Potassium, and Chloride. **Why the other options are incorrect:** * **Zinc (A), Copper (B), and Selenium (C)** are all classified as **Trace elements**. These are required in the diet in amounts less than **100 mg/day** (often <20 mg/day). * **Zinc** is a cofactor for over 300 enzymes (e.g., Carbonic anhydrase, Alcohol dehydrogenase). * **Copper** is essential for iron metabolism (Ceruloplasmin) and collagen cross-linking (Lysyl oxidase). * **Selenium** is a vital component of the antioxidant enzyme **Glutathione peroxidase**. **High-Yield Clinical Pearls for NEET-PG:** * **Ultra-trace elements:** Required in microgram quantities (e.g., Chromium, Manganese, Molybdenum, Iodine). * **Zinc Deficiency:** Characterized by Acrodermatitis enteropathica, poor wound healing, and hypogonadism. * **Copper Deficiency:** Seen in **Menkes Kinky Hair Syndrome** (ATP7A mutation); excess is seen in **Wilson’s Disease** (ATP7B mutation). * **Selenium Deficiency:** Associated with **Keshan disease** (cardiomyopathy).

Question 135: Which of the following statements is true regarding the Recommended Dietary Allowance (RDA)?

A. RDA is statistically defined as two standard deviations above the estimated average requirement (EAR). (Correct Answer)
B. RDA is statistically defined as equal to the estimated average requirement.
C. RDA is statistically defined as equal to the adequate intake.
D. RDA is defined as the recommended minimum requirement.

Explanation: ### Explanation **1. Why Option A is Correct:** The **Recommended Dietary Allowance (RDA)** is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (**97–98%**) healthy individuals in a particular life stage and gender group. Statistically, the RDA is derived from the **Estimated Average Requirement (EAR)**, which is the intake level estimated to meet the needs of 50% of the population. To ensure coverage for almost the entire population, the RDA is set at **two standard deviations (2 SD)** above the EAR: $$\text{RDA} = \text{EAR} + 2 \text{SD}_{\text{EAR}}$$ This mathematical buffer accounts for individual variations in nutrient needs. **2. Why Other Options are Incorrect:** * **Option B:** The EAR meets the needs of only **50%** of the population. Using this as a guideline would leave half the population at risk of deficiency. * **Option C:** **Adequate Intake (AI)** is used only when there is insufficient scientific evidence to calculate an EAR (and subsequently an RDA). They are distinct categories of Dietary Reference Intakes (DRIs). * **Option D:** The RDA is not a "minimum" requirement to prevent acute deficiency (like scurvy); it is a goal for optimal long-term health in healthy individuals. **3. High-Yield NEET-PG Pearls:** * **EAR vs. RDA:** If you know the EAR, you can calculate the RDA. If the EAR cannot be determined, an RDA cannot be set. * **Tolerable Upper Intake Level (UL):** The highest level of daily nutrient intake that is likely to pose no risk of adverse health effects. Intake above the UL increases the risk of toxicity. * **Energy Requirements:** Unlike vitamins/minerals, the **Estimated Energy Requirement (EER)** is set at the **mean (average)** requirement, not 2 SD above, to prevent the risk of overconsumption and obesity.

Question 136: Which of the following minerals potentiates the action of insulin?

A. Molybdenum
B. Chromium (Correct Answer)
C. Manganese
D. Selenium

Explanation: **Explanation:** **Chromium (Cr³⁺)** is the correct answer because it is an essential trace element that plays a vital role in carbohydrate and lipid metabolism. It functions as a component of **Chromodulin** (also known as Glucose Tolerance Factor or GTF). **Mechanism:** Chromium potentiates insulin action by facilitating the binding of insulin to its cell surface receptors and increasing the number of insulin receptors. It enhances the tyrosine kinase activity of the insulin receptor, thereby increasing insulin sensitivity and improving glucose uptake by peripheral tissues. **Analysis of Incorrect Options:** * **Molybdenum:** Acts as a cofactor for metalloenzymes such as Xanthine oxidase (involved in purine catabolism), Sulfite oxidase, and Aldehyde oxidase. * **Manganese:** A cofactor for enzymes like Pyruvate carboxylase (gluconeogenesis), Arginase (urea cycle), and Superoxide dismutase (mitochondrial antioxidant). * **Selenium:** A vital component of the enzyme **Glutathione peroxidase**, which protects cells against oxidative damage by neutralizing hydrogen peroxide. **High-Yield Clinical Pearls for NEET-PG:** * **Chromium Deficiency:** Leads to impaired glucose tolerance (IGT), glycosuria, and a syndrome mimicking Type 2 Diabetes Mellitus. * **Chromium Supplementation:** Often discussed in the management of PCOS and metabolic syndrome to reduce insulin resistance. * **Key Association:** Remember **Chromium = Chromodulin = Insulin Potentiation.**

Question 137: Which of the following statements about nutrition is FALSE?

A. Vitamin A deficiency does not typically manifest for a year or more after cessation of intake.
B. Zinc deficiency is associated with pulmonary fibrosis. (Correct Answer)
C. Selenium deficiency can lead to cardiomyopathy.
D. A diet high in calcium can reduce iron absorption.

Explanation: **Explanation:** **Why Option B is the Correct (False) Statement:** Zinc deficiency is not associated with pulmonary fibrosis. Instead, its classic clinical presentation includes **acrodermatitis enteropathica** (periorificial and acral dermatitis), alopecia, diarrhea, impaired wound healing, hypogonadism, and growth retardation. Zinc is a critical cofactor for over 300 enzymes, including carbonic anhydrase and alkaline phosphatase. While zinc toxicity (via inhalation) can cause lung irritation, deficiency has no established link to pulmonary fibrosis. **Analysis of Incorrect (True) Options:** * **Option A:** Vitamin A is a fat-soluble vitamin stored extensively in the **Ito cells** of the liver. These reserves are sufficient to last for 1–2 years in a well-nourished individual, meaning clinical symptoms like night blindness take a long time to manifest after intake stops. * **Option C:** Selenium is a component of **glutathione peroxidase**. Its deficiency leads to **Keshan disease**, an endemic cardiomyopathy characterized by cardiac enlargement and heart failure (originally described in China). * **Option D:** Calcium and iron compete for the same transport mechanisms in the intestinal mucosa (specifically the DMT1 transporter). High calcium intake, particularly from dairy or supplements, significantly inhibits the absorption of non-heme iron. **High-Yield NEET-PG Pearls:** 1. **Zinc:** Essential for "Zinc Finger" motifs in DNA-binding proteins. Deficiency causes **dysgeusia** (distorted taste). 2. **Selenium:** Deficiency is also linked to **Kashin-Beck disease** (an osteoarthropathy). 3. **Iron Absorption:** Enhanced by Vitamin C (reduces $Fe^{3+}$ to $Fe^{2+}$) and inhibited by phytates, oxalates, and calcium. 4. **Vitamin A:** The earliest clinical sign of deficiency is **Nyctalopia** (night blindness); the earliest conjunctival sign is **Conjunctival Xerosis**.

Question 138: Vitamin K dependent clotting factors of hepatic origin are all of the following except?

A. II
B. VI
C. VIII (Correct Answer)
D. X

Explanation: **Explanation:** The correct answer is **C (Factor VIII)**. The synthesis of certain coagulation factors requires **Vitamin K** as a cofactor for the enzyme **gamma-glutamyl carboxylase**. This enzyme catalyzes the carboxylation of glutamic acid residues on pro-clotting proteins, allowing them to bind calcium and adhere to phospholipid surfaces. **Why Factor VIII is the correct answer:** While most clotting factors are synthesized in the liver, **Factor VIII** is unique. It is primarily produced in the **sinusoidal endothelial cells** of the liver and extrahepatic endothelial cells, rather than the hepatocytes. More importantly, Factor VIII is **not Vitamin K-dependent**. Its deficiency leads to Hemophilia A. **Analysis of incorrect options:** * **Option A (Factor II - Prothrombin):** This is a Vitamin K-dependent serine protease synthesized in the liver hepatocytes. * **Option B (Factor VII):** This factor has the shortest half-life of all clotting factors and is the first to decrease during Vitamin K deficiency or Warfarin therapy. * **Option D (Factor X):** This is a key component of the common pathway and is Vitamin K-dependent. **High-Yield Clinical Pearls for NEET-PG:** * **Vitamin K-dependent factors:** Remember the mnemonic **"1972"** (Factors **II, VII, IX, and X**). * **Anticoagulant proteins:** Proteins **C and S** are also Vitamin K-dependent and act as natural anticoagulants. * **Warfarin Mechanism:** It inhibits **Vitamin K Epoxide Reductase (VKOR)**, preventing the recycling of Vitamin K, thereby inhibiting the synthesis of these factors. * **PT vs. aPTT:** Vitamin K deficiency or Warfarin therapy primarily prolongs the **Prothrombin Time (PT)** initially due to the short half-life of Factor VII.

Question 139: Net Protein Utilization is maximum (100%) for:

A. Ragi
B. Egg (Correct Answer)
C. Soyabean
D. Pulses

Explanation: ### Explanation **Net Protein Utilization (NPU)** is a measure of protein quality that represents the proportion of dietary protein that is actually retained by the body for growth and maintenance. It is calculated as: $NPU = \frac{\text{Nitrogen Retained}}{\text{Nitrogen Intake}} \times 100$ **Why Egg is the Correct Answer:** Egg protein is considered the **"Reference Protein"** in nutrition. It has an NPU of approximately **94–100%** because it contains all essential amino acids in the ideal proportions required by the human body. Due to its near-perfect digestibility and utilization, it serves as the gold standard against which all other dietary proteins are compared. **Analysis of Incorrect Options:** * **Soyabean (Option C):** While soy is the best plant-based protein source with a high biological value, its NPU is approximately **60–70%**. It is limited by the presence of anti-nutritional factors (like trypsin inhibitors) and is relatively deficient in sulfur-containing amino acids (Methionine). * **Pulses (Option D):** Most pulses have an NPU ranging from **40–60%**. They are typically deficient in Methionine but rich in Lysine. * **Ragi (Option A):** Ragi (Finger Millet) is a good source of calcium and fiber, but its protein utilization is significantly lower than animal sources, typically falling below **50%**. **High-Yield Clinical Pearls for NEET-PG:** * **Biological Value (BV):** Egg has the highest BV (100). BV measures the percentage of *absorbed* nitrogen retained, whereas NPU accounts for *digestibility*. * **Limiting Amino Acids:** * Pulses/Legumes: Limited by **Methionine**. * Cereals (Wheat/Rice): Limited by **Lysine**. * **Mutual Supplementation:** Combining cereals and pulses (e.g., Khichdi) improves the overall NPU of a vegetarian diet because they provide the amino acids the other lacks. * **PDCAAS:** The Protein Digestibility Corrected Amino Acid Score is the current FAO/WHO standard; Egg and Soy protein isolate both score **1.0** (maximum).

Question 140: An obese individual is brought to the emergency room by a concerned friend. The patient has been on a self-imposed "starvation diet" for four months, and has lost 60 pounds while consuming only water and vitamin pills. If extensive blood studies were performed, which of the following would be expected to be elevated?

A. Acetoacetic acid (Correct Answer)
B. Alanine
C. Bicarbonate
D. Chylomicrons

Explanation: ### Explanation **Correct Option: A. Acetoacetic acid** During prolonged starvation (4 months), the body undergoes metabolic adaptation to preserve glucose for the brain and switch to fat utilization. As glycogen stores are depleted within 24 hours, the liver begins **ketogenesis**. Fatty acids are mobilized from adipose tissue and converted into ketone bodies—**acetoacetic acid**, $\beta$-hydroxybutyrate, and acetone—in the liver mitochondria. After several weeks of starvation, the brain adapts to use these ketone bodies as its primary energy source, significantly reducing the need for gluconeogenesis and sparing muscle protein. **Why Incorrect Options are Wrong:** * **B. Alanine:** During early starvation, alanine is the primary glucogenic amino acid released from muscle. However, in prolonged starvation, muscle proteolysis decreases to conserve body protein, leading to **decreased** plasma alanine levels. * **C. Bicarbonate:** The accumulation of ketone bodies (which are organic acids) leads to a state of **metabolic acidosis**. To buffer the excess $H^+$ ions, serum bicarbonate levels will be **decreased**, not elevated. * **D. Chylomicrons:** Chylomicrons are lipoproteins synthesized in the intestine to transport **dietary (exogenous) lipids**. Since the patient is consuming only water and vitamins, no dietary fats are being ingested, making chylomicron levels negligible. **NEET-PG High-Yield Pearls:** * **Ketogenesis Rate-Limiting Step:** HMG-CoA Synthase (Mitochondrial). * **Organ that cannot use Ketones:** The **Liver** (lacks thiophorase/$\beta$-ketoacyl-CoA transferase) and **RBCs** (lack mitochondria). * **Starvation Fuel Shift:** * *Early (1-3 days):* Gluconeogenesis (Protein breakdown). * *Late (>3 days):* Ketolysis (Fat/Protein sparing). * **Major Ketone Body:** $\beta$-hydroxybutyrate is typically the most abundant ketone in the blood during ketoacidosis.

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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