Nutrition and Metabolism — MCQs

A 42-year-old man with a small-bowel fistula has been receiving TPN with a standard hypertonic glucose-amino acid solution for the previous 3 weeks. The patient has developed scaly, hyperpigmented lesions over the acral surfaces of elbows and knees, resembling acrodermatitis enteropathica. What is the most likely cause of this condition?

Q149Easy

Which of the following is NOT a trace element required for human nutrition?

Q150Easy

What is the mechanism of action of Calcitriol?

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 141: Which of the following statements is true regarding Basal Metabolic Rate (BMR)?

A. BMR is not influenced by energy intake.
B. BMR increases in response to starvation.
C. BMR may decrease up to 50% during periods of starvation. (Correct Answer)
D. BMR is not responsive to changes in hormonal levels.

Explanation: ### Explanation **1. Why the Correct Answer is Right:** Basal Metabolic Rate (BMR) represents the minimum energy expenditure required to maintain vital functions (heartbeat, respiration, kidney function) at rest. During periods of **starvation or chronic calorie restriction**, the body initiates an adaptive mechanism to conserve energy and ensure survival. This involves a reduction in sympathetic nervous system activity and a decrease in the peripheral conversion of T4 to the active T3 hormone. Consequently, the BMR can drop significantly—by as much as **50%**—to minimize the depletion of endogenous energy stores (glycogen, fat, and muscle protein). **2. Analysis of Incorrect Options:** * **Option A:** BMR is heavily influenced by energy intake. Overfeeding can slightly increase BMR (thermogenesis), while underfeeding significantly decreases it. * **Option B:** This is the opposite of physiological reality. BMR **decreases** during starvation to prevent rapid metabolic exhaustion. * **Option D:** BMR is highly sensitive to hormones. **Thyroid hormones (T3, T4)** are the primary regulators; hyperthyroidism increases BMR, while hypothyroidism decreases it. Epinephrine and cortisol also influence metabolic rates. **3. High-Yield Facts for NEET-PG:** * **Surface Area Rule:** BMR is directly proportional to the body surface area (Rubner’s Law). * **Gender & Age:** BMR is generally higher in males (due to higher muscle mass) and decreases with age (approx. 2% per decade after age 20). * **Specific Dynamic Action (SDA):** Also known as the Thermic Effect of Food; **Proteins** have the highest SDA (30%), followed by carbohydrates (5-6%) and fats (4%). * **Fever:** For every 1°C rise in body temperature, BMR increases by approximately **12-13%**.

Question 142: A 50-year-old diabetic man asks about a low glycemic index diet. Which of the following food items has a low glycemic index?

A. Brown rice
B. White bread
C. Corn flakes
D. Whole grains (Correct Answer)

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 **low GI (≤ 55)** are digested and absorbed slowly, causing a gradual rise in blood sugar, which is ideal for managing Diabetes Mellitus. **Why Whole Grains are correct:** Whole grains (like oats, barley, and broken wheat) contain intact bran and germ layers. These layers are rich in **dietary fiber**, which acts as a physical barrier to digestive enzymes and slows down the hydrolysis of starch. This results in a slow, sustained release of glucose into the bloodstream. **Analysis of Incorrect Options:** * **White bread (GI ≈ 75):** Made from refined flour (maida), it lacks fiber and is rapidly hydrolyzed into glucose, making it a high-GI food. * **Corn flakes (GI ≈ 80-90):** These are highly processed and gelatinized, leading to a very rapid glycemic response. * **Brown rice (GI ≈ 68):** While healthier than white rice, brown rice typically falls into the **medium GI** category. In the context of this question, "Whole grains" is the most accurate representation of a low-GI choice. **NEET-PG High-Yield Pearls:** 1. **Glycemic Load (GL):** A more accurate predictor of glycemic response than GI, calculated as: $GL = \frac{GI \times \text{Net Carbohydrates (g)}}{100}$. 2. **Factors lowering GI:** High fiber content, presence of fat/protein, acidity (vinegar/lemon), and less processing/cooking time. 3. **Clinical Significance:** Low GI diets improve HbA1c levels, reduce insulin resistance, and aid in weight management by increasing satiety.

Question 143: Which of the following clinical situations is associated with increased intestinal absorption?

A. Wilson disease (Correct Answer)
B. Pernicious anemia
C. Chronic calcific pancreatitis
D. Cystic fibrosis

Explanation: **Explanation:** The correct answer is **Wilson disease (Option A)**. Wilson disease is an autosomal recessive disorder caused by mutations in the **ATP7B gene**, which encodes a copper-transporting P-type ATPase. While the primary defect is impaired biliary excretion of copper and failure to incorporate copper into ceruloplasmin, the resulting systemic copper deficiency (at a cellular level) and altered homeostasis lead to a compensatory **increase in intestinal copper absorption** via the DMT1 and CTR1 transporters. This creates a state of progressive copper overload in the liver, brain, and cornea. **Why the other options are incorrect:** * **Pernicious anemia:** This is characterized by **decreased absorption** of Vitamin B12 due to the lack of Intrinsic Factor (IF) resulting from autoimmune destruction of gastric parietal cells. * **Chronic calcific pancreatitis:** This leads to exocrine pancreatic insufficiency. The lack of digestive enzymes (lipase, protease) results in **malabsorption** of fats, proteins, and fat-soluble vitamins. * **Cystic fibrosis:** Mutations in the CFTR gene cause thick secretions that obstruct pancreatic ducts, leading to enzyme deficiency and significant **intestinal malabsorption** (steatorrhea). **High-Yield Clinical Pearls for NEET-PG:** * **Wilson Disease Triad:** Liver disease, neurological symptoms (basal ganglia involvement), and **Kayser-Fleischer (KF) rings** in the Descemet membrane of the cornea. * **Diagnosis:** Low serum ceruloplasmin, increased urinary copper excretion, and increased hepatic copper content on biopsy. * **Treatment:** Copper chelators like **D-penicillamine** or Trientine, and Zinc (which induces metallothionein in enterocytes to block further copper absorption).

Question 144: An egg yields about how many kcal of energy?

A. 70 kcal (Correct Answer)
B. 80 kcal
C. 90 kcal
D. 100 kcal

Explanation: **Explanation:** The energy content of a standard whole chicken egg (average weight 50–60g) is approximately **70 kcal**. This value is derived from its macronutrient composition: a typical egg contains roughly **6g of protein** and **5g of fat**, with negligible carbohydrates. Using the Atwater factors (4 kcal/g for protein and 9 kcal/g for fat), the calculation (6×4) + (5×9) yields approximately 69 kcal, which is rounded to 70 kcal in standard nutritional and medical textbooks. **Analysis of Options:** * **Option A (70 kcal):** This is the standard physiological value accepted by the WHO and nutritional guidelines for a medium-to-large egg. * **Options B, C, and D (80, 90, 100 kcal):** These values overestimate the caloric density of a standard egg. While an extra-large or jumbo egg might approach 80–90 kcal, for medical examinations, the "reference egg" is always calculated at 70 kcal. **High-Yield Facts for NEET-PG:** * **Biological Value (BV):** The egg has the highest Biological Value (100) among all natural foods and is considered the **"Reference Protein"** against which other proteins are compared. * **Net Protein Utilization (NPU):** For an egg, the NPU is approximately 96, indicating extremely high digestibility and absorption. * **Limiting Amino Acids:** Eggs contain all essential amino acids in balanced proportions; they are notably rich in **Leucine** and **Choline**. * **Fat Content:** Most of the 70 kcal (and all the cholesterol/fat-soluble vitamins) are concentrated in the **yolk**, while the white (albumin) contains primarily protein and water.

Question 145: What is seen in severe starvation?

A. Albuminuria
B. Ketonuria (Correct Answer)
C. Hematuria
D. All of the above

Explanation: **Explanation:** In severe starvation, the body undergoes a metabolic shift to maintain energy homeostasis. Once glycogen stores are exhausted (within 24 hours), the body initiates **gluconeogenesis** and **lipolysis**. **Why Ketonuria is the Correct Answer:** During prolonged starvation, the breakdown of adipose tissue releases large amounts of free fatty acids. These undergo $\beta$-oxidation in the liver to produce **Acetyl-CoA**. Because the availability of oxaloacetate is limited (as it is diverted toward gluconeogenesis), Acetyl-CoA cannot enter the TCA cycle efficiently. Instead, it is diverted into **ketogenesis**, producing ketone bodies (acetoacetate, $\beta$-hydroxybutyrate, and acetone). When the rate of ketone production exceeds the peripheral tissue's ability to utilize them, they accumulate in the blood (ketonemia) and are excreted in the urine (**ketonuria**). **Why Other Options are Incorrect:** * **Albuminuria:** This refers to the presence of albumin in the urine, typically a sign of glomerular damage (e.g., Nephrotic syndrome or Diabetic Nephropathy). Starvation leads to muscle wasting and hypoalbuminemia, but not typically the leakage of albumin through the kidneys. * **Hematuria:** This is the presence of blood in the urine, usually caused by trauma, stones, malignancy, or infections of the urinary tract. It is not a physiological consequence of starvation. **High-Yield Clinical Pearls for NEET-PG:** * **Ketone Bodies:** They are water-soluble energy sources synthesized in the **liver mitochondria** but **cannot** be used by the liver itself (due to the absence of the enzyme *thiophorase*). * **Brain Adaptation:** After 2–3 weeks of starvation, the brain adapts to derive approximately 60–75% of its energy from ketone bodies. * **Rothera’s Test:** Used to detect acetone and acetoacetate in urine (appears as a permanganate/purple ring). Note: It does *not* detect $\beta$-hydroxybutyrate.

Question 146: A 40-year-old woman, who has lost 36 kg over the past 2 years, presents with hair loss. She reports following a strict fat-free diet. Her alopecia is probably related to a deficiency of which of the following vitamins?

A. Vitamin A (Correct Answer)
B. Vitamin C
C. Vitamin D
D. Vitamin E

Explanation: **Explanation:** The patient’s presentation of significant weight loss and a strict **fat-free diet** indicates a deficiency in **fat-soluble vitamins (A, D, E, and K)**, which require dietary lipids for micelle formation and absorption in the small intestine. **Why Vitamin A is the Correct Answer:** Vitamin A (Retinol) is essential for the maintenance of epithelial tissues and hair follicle integrity. A deficiency leads to **follicular hyperkeratosis** (phrynoderma) and disruption of the hair growth cycle, resulting in **alopecia**. While Vitamin A toxicity is a more famous cause of hair loss, chronic deficiency due to severe fat malabsorption or restriction also manifests as thinning hair and skin changes. **Analysis of Incorrect Options:** * **Vitamin C:** A water-soluble vitamin. Deficiency causes **Scurvy**, characterized by "corkscrew hairs," perifollicular hemorrhages, and bleeding gums, but not typically diffuse alopecia. Its absorption is not dependent on dietary fat. * **Vitamin D:** While Vitamin D receptors play a role in hair cycling, clinical deficiency primarily manifests as **Rickets** (children) or **Osteomalacia** (adults). It is less commonly the primary driver of alopecia compared to Vitamin A in the context of fat restriction. * **Vitamin E:** Acts as an antioxidant. Deficiency is rare but leads to **hemolytic anemia** and neurological symptoms (posterior column signs); it is not a classic cause of alopecia. **NEET-PG High-Yield Pearls:** * **Fat-Soluble Vitamins:** Remember the mnemonic **KADE**. Their absorption depends on pancreatic lipases and bile salts. * **Phrynoderma (Toad Skin):** A classic sign of Vitamin A deficiency involving follicular hyperkeratosis on the extensor surfaces. * **Zinc Deficiency:** Another high-yield cause of alopecia in patients with malabsorption (presents as Acrodermatitis enteropathica). * **Vitamin A Toxicity:** Also causes alopecia, along with pseudotumor cerebri and hepatosplenomegaly.

Question 147: Refeeding syndrome is primarily associated with the release of which hormone?

A. Growth hormone
B. Glucocorticoids
C. Insulin (Correct Answer)
D. Thyroxine

Explanation: **Explanation:** Refeeding syndrome is a potentially fatal metabolic complication that occurs when nutritional support is reintroduced to severely malnourished or starved patients. **Why Insulin is the Correct Answer:** During prolonged starvation, the body shifts from using glucose to using fat and ketones for energy; insulin levels are low, and glucagon levels are high. When feeding is reintroduced (especially carbohydrates), there is a sudden, massive surge in **Insulin** secretion. Insulin acts as an anabolic hormone, driving glucose, water, and electrolytes—specifically **Potassium, Magnesium, and Phosphate**—from the extracellular space into the cells. This leads to profound **hypophosphatemia** (the hallmark of the syndrome), hypokalemia, and hypomagnesemia, which can cause cardiac arrhythmias, seizures, and respiratory failure. **Why Incorrect Options are Wrong:** * **Growth Hormone (A):** While involved in growth and metabolism, it does not surge acutely in response to refeeding nor does it drive the rapid intracellular electrolyte shifts seen in this syndrome. * **Glucocorticoids (B):** Cortisol levels are typically elevated during the stress of starvation (catabolic state) and decrease upon refeeding. They do not mediate the acute electrolyte shifts. * **Thyroxine (D):** Thyroid hormones regulate the basal metabolic rate. While starvation can lead to "Sick Euthyroid Syndrome," thyroxine is not the primary mediator of the refeeding response. **High-Yield Clinical Pearls for NEET-PG:** * **Hallmark Electrolyte Abnormality:** Hypophosphatemia. * **Vitamin Deficiency:** Thiamine (Vitamin B1) deficiency is often exacerbated during refeeding as it is a co-factor for glucose metabolism, potentially leading to Wernicke’s Encephalopathy. * **Prevention:** "Start low and go slow" with caloric intake and proactively supplement thiamine and electrolytes.

Question 148: A 42-year-old man with a small-bowel fistula has been receiving TPN with a standard hypertonic glucose-amino acid solution for the previous 3 weeks. The patient has developed scaly, hyperpigmented lesions over the acral surfaces of elbows and knees, resembling acrodermatitis enteropathica. What is the most likely cause of this condition?

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

Explanation: **Explanation:** The clinical presentation of scaly, hyperpigmented lesions over acral surfaces (elbows, knees, and periorificial areas) in a patient on long-term Total Parenteral Nutrition (TPN) is classic for **Zinc deficiency**. 1. **Why Zinc Deficiency is correct:** Zinc is an essential cofactor for over 300 enzymes, including those involved in DNA synthesis and cell division. Patients on TPN are at high risk if supplementation is inadequate, especially those with small-bowel fistulas, as zinc is primarily excreted via gastrointestinal secretions. The symptoms mimic **Acrodermatitis Enteropathica**, an autosomal recessive disorder of zinc absorption. Key features include dermatitis (acral and periorificial), alopecia, diarrhea, and impaired wound healing. 2. **Why other options are incorrect:** * **Copper deficiency:** Typically presents with hematological abnormalities (microcytic anemia, neutropenia) and neurological symptoms (ataxia, myelopathy) resembling Vitamin B12 deficiency. * **Chromium deficiency:** Primarily manifests as **glucose intolerance** or insulin resistance, as chromium facilitates insulin binding to its receptor. * **Manganese deficiency:** Rare in humans; may cause weight loss, transient dermatitis, and changes in hair color/growth, but does not present with acral dermatitis. **High-Yield Clinical Pearls for NEET-PG:** * **Zinc & TPN:** Always suspect Zinc deficiency in TPN patients with skin rashes or poor wound healing. * **Zinc & Enzymes:** It is a component of **Carbonic Anhydrase**, **Alkaline Phosphatase**, and **RNA Polymerase**. * **Selenium Deficiency:** Another TPN-related deficiency to remember; it causes **Cardiomyopathy** (Keshan disease). * **Iodine Deficiency:** Causes goiter and hypothyroidism.

Question 149: Which of the following is NOT a trace element required for human nutrition?

A. Magnesium (Mg)
B. Calcium (Ca)
C. Zinc (Zn) (Correct Answer)
D. Potassium (K)

Explanation: **Explanation:** The classification of minerals in human nutrition is based on the daily dietary requirement. Minerals are divided into **Macro-minerals** (required in amounts >100 mg/day) and **Micro-minerals/Trace elements** (required in amounts <100 mg/day). **Why Zinc (Zn) is the correct answer:** Zinc is classified as a **trace element**. The average adult requirement for Zinc is approximately 8–11 mg/day. It serves as a vital cofactor for over 300 enzymes, including Carbonic Anhydrase, Alcohol Dehydrogenase, and DNA/RNA polymerases. Since the question asks which of the following is a trace element (noting the checkmark provided in the prompt), Zinc fits this classification perfectly. **Analysis of Incorrect Options (Macro-minerals):** * **Magnesium (Mg):** A macro-mineral required in amounts of ~300–400 mg/day. It is essential for ATP-related reactions and bone structure. * **Calcium (Ca):** The most abundant mineral in the body and a major macro-mineral. The RDA is ~1000 mg/day. * **Potassium (K):** The primary intracellular cation and a macro-mineral. The daily requirement is high (~3500–4700 mg/day) to maintain membrane potential. **High-Yield Clinical Pearls for NEET-PG:** * **Ultra-trace elements:** Required in <1 mg/day (e.g., Selenium, Manganese, Molybdenum). * **Zinc Deficiency:** Characterized by **Acrodermatitis enteropathica**, poor wound healing, hypogeusia (decreased taste), and growth retardation. * **Zinc Fingers:** These are structural motifs in proteins that help in binding DNA, crucial for steroid hormone receptor function. * **Chromium:** A trace element essential for insulin action (Glucose Tolerance Factor).

Question 150: What is the mechanism of action of Calcitriol?

A. Decreased calcium resorption from bone
B. Increased calcium absorption from the intestine (Correct Answer)
C. Decreased calcium reabsorption by the kidney
D. Decreased calcium absorption from the intestine

Explanation: **Explanation:** Calcitriol ($1,25\text{-(OH)}_2\text{D}_3$) is the active form of Vitamin D. Its primary physiological role is to maintain plasma calcium levels by acting on the intestine, bone, and kidneys. **Why the correct answer is right:** Calcitriol acts as a steroid hormone. It enters intestinal mucosal cells and binds to a nuclear **Vitamin D Receptor (VDR)**. This complex promotes the transcription of **Calbindin** (a calcium-binding protein). Calbindin facilitates the transport of dietary calcium across the intestinal brush border membrane into the circulation, significantly **increasing intestinal calcium absorption**. **Analysis of Incorrect Options:** * **Option A:** Calcitriol actually **increases** bone resorption (in conjunction with PTH) by stimulating osteoclast maturation to mobilize calcium into the blood when levels are low. * **Option C:** Calcitriol **increases** (not decreases) the renal reabsorption of calcium and phosphorus in the distal convoluted tubules, minimizing loss in urine. * **Option D:** This is the opposite of Calcitriol’s primary function. **High-Yield Clinical Pearls for NEET-PG:** * **Rate-limiting step:** The conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D by the enzyme **1-alpha-hydroxylase** in the kidney (stimulated by PTH). * **Dual Effect on Phosphorus:** Unlike PTH (which is phosphaturic), Calcitriol increases both Calcium and Phosphorus levels in the blood. * **Deficiency:** Leads to **Rickets** in children (defective mineralization of osteoid) and **Osteomalacia** in adults. * **VDR Mutation:** Mutations in the Vitamin D Receptor lead to Vitamin D-Dependent Rickets Type II.

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Macronutrients and Energy Requirements

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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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Functional Foods and Nutraceuticals

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Dietary Guidelines and Recommendations

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