Nutrition and Metabolism Practice Questions

Q: A child presents with alopecia, hyperpigmentation, hypogonadism, and a rash on the genital area and mouth. What deficiency is most likely responsible?

Zinc deficiency. The clinical presentation described is a classic manifestation of **Zinc deficiency**. Zinc is a vital trace element required for over 300 metalloenzymes (e.g., Carbonic anhydrase, Alkaline phosphatase, RNA polymerase). ### **Why Zinc Deficiency is Correct** The triad of **alopecia, periorificial dermatitis** (rash around the mouth, eyes, and genitals), and **diarrhea** is pathognomonic for severe zinc deficiency. Zinc is essential for DNA synthesis and cell division; hence, rapidly dividing tissues like skin and the immune system are affected first. In children, it also leads to **hypogonadism** (delayed sexual maturation), growth retardation, and impaired wound healing. ### **Why Other Options are Incorrect** * **Iron deficiency:** Primarily presents with microcytic hypochromic anemia, pica, and koilonychia (spoon-shaped nails), but not periorificial rashes or hypogonadism. * **Calcium deficiency:** Presents with neuromuscular irritability (tetany, Chvostek/Trousseau signs), rickets in children, or osteomalacia in adults. * **Copper deficiency:** Leads to Menkes kinky hair syndrome (brittle, "steely" hair), microcytic anemia (refractory to iron), and neurological degeneration, but not the specific periorificial rash seen here. ### **NEET-PG High-Yield Pearls** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder caused by a mutation in the *SLC39A4* gene, leading to impaired intestinal zinc absorption. It presents identically to the question above. * **Enzyme Marker:** Serum **Alkaline Phosphatase (ALP)** levels often decrease in zinc deficiency because ALP is a zinc-dependent enzyme. * **Other features:** Zinc deficiency is also associated with **dysgeusia** (distorted taste) and **impaired night vision** (as it helps mobilize Vitamin A from the liver).

Q: What is the approximate total body iodine content?

50 mg. **Explanation:** The total body iodine content in a healthy adult is approximately **50 mg**. Iodine is an essential trace element primarily required for the synthesis of thyroid hormones (T3 and T4). **Distribution of Iodine:** * **Thyroid Gland:** Contains about **70–80% (approx. 30–40 mg)** of the total body iodine. It is stored here mostly in the form of thyroglobulin. * **Extrathyroidal Tissues:** The remaining 20–30% is distributed in the salivary glands, gastric mucosa, mammary glands, and blood. **Analysis of Options:** * **A (20 mg):** This value is too low for a healthy adult; it represents only the amount typically found within the thyroid gland itself in some populations, not the total body. * **B (30 mg) & C (40 mg):** While these values represent the iodine content specifically sequestered within the thyroid gland, they do not account for the iodine circulating in the plasma or stored in other tissues. * **D (50 mg):** This is the standard physiological value cited in major biochemistry textbooks (like Harper’s and Vasudevan) for the total body pool. **High-Yield Clinical Pearls for NEET-PG:** 1. **Daily Requirement:** The RDA for a normal adult is **150 μg/day**. This increases to **220 μg/day** during pregnancy and **290 μg/day** during lactation. 2. **Iodine Trap:** The thyroid gland concentrates iodine against a steep gradient (30:1) via the **Sodium-Iodide Symporter (NIS)**. 3. **Excretion:** Over 90% of ingested iodine is excreted via **urine**, making urinary iodine concentration the best epidemiological indicator of iodine status. 4. **Wolff-Chaikoff Effect:** A transient reduction in thyroid hormone levels caused by the ingestion of a large amount of iodine.

Q: Which of the following laboratory values is NOT typically monitored in patients at risk for refeeding syndrome?

Ammonium. **Explanation:** **Refeeding Syndrome** is a potentially fatal condition that occurs when nutritional support (enteral or parenteral) is reintroduced to severely malnourished patients. The underlying pathophysiology involves a shift from a **catabolic state** (fat metabolism) to an **anabolic state** (carbohydrate metabolism). 1. **Why Ammonium is the Correct Answer:** Ammonium levels are not typically monitored because the primary metabolic derangements in refeeding syndrome involve **electrolytes and minerals**, not nitrogenous waste products. While urea cycle defects or liver failure involve ammonia, refeeding syndrome is characterized by the sudden intracellular shift of ions driven by **insulin secretion**. 2. **Why the Other Options are Incorrect:** * **Phosphate (C):** Hypophosphatemia is the **hallmark** of refeeding syndrome. Insulin causes cells to take up glucose and phosphate (for ATP production), leading to severe depletion in the blood, which can cause respiratory failure and cardiac arrest. * **Magnesium (B) & Calcium (A):** Insulin also promotes the intracellular shift of magnesium and potassium. Hypomagnesemia can lead to arrhythmias and neuromuscular irritability. While phosphate is the primary concern, monitoring divalent cations like Calcium and Magnesium is standard protocol to prevent multi-organ dysfunction. **NEET-PG High-Yield Pearls:** * **The "Key Driver":** Insulin is the hormone responsible for the electrolyte shifts. * **Hallmark Sign:** Severe **Hypophosphatemia**. * **Clinical Presentation:** Peripheral edema (due to sodium/water retention), arrhythmias, seizures, and heart failure. * **Prevention Strategy:** "Start low and go slow" (initiate caloric intake at 50% of requirements and monitor electrolytes daily). * **Vitamin Deficiency:** **Thiamine (B1)** deficiency is often exacerbated during refeeding as it is a cofactor for carbohydrate metabolism (Wernicke’s encephalopathy risk).

Q: What is the best indicator of protein quality?

Digestible Indispensable Amino Acid Score (DIAAS). **Explanation:** Protein quality is determined by the profile of essential amino acids and their bioavailability. While several methods exist, the **Digestible Indispensable Amino Acid Score (DIAAS)** is currently recognized by the FAO/WHO as the "gold standard" and best indicator. **Why DIAAS is the Correct Answer:** Unlike older methods, DIAAS measures the digestibility of **individual** amino acids at the end of the small intestine (**ileal digestibility**). This is more accurate because it excludes amino acids fermented by bacteria in the large intestine, which are not available for protein synthesis. It also does not "truncate" scores, allowing for a true comparison of high-quality proteins. **Analysis of Incorrect Options:** * **Amino Acid Score (Chemical Score):** This only compares the amino acid composition of a test protein to a reference protein (usually egg albumin). It fails to account for how well the protein is actually digested and absorbed. * **Protein Digestibility Corrected Amino Acid Score (PDCAAS):** Previously the gold standard, it uses **fecal digestibility**, which overestimates quality. It also caps scores at 1.0 (100%), meaning it cannot distinguish between high-quality proteins like milk vs. soy. * **Protein Efficiency Ratio (PER):** Based on the weight gain of growing rats. It is less relevant to human adult requirements and is time-consuming to measure. **High-Yield Clinical Pearls for NEET-PG:** * **Reference Protein:** Egg albumin (Biological Value = 100) is the standard for comparison. * **Limiting Amino Acids:** Pulses are deficient in **Methionine**, while Cereals are deficient in **Lysine**. * **Biological Value (BV):** Measures the proportion of absorbed nitrogen that is retained by the body. * **Net Protein Utilization (NPU):** $BV \times \text{Digestibility Coefficient} / 100$. It is a better practical measure of protein quality than BV alone.

Question 1

A child presents with alopecia, hyperpigmentation, hypogonadism, and a rash on the genital area and mouth. What deficiency is most likely responsible?

Accepted Answer

Zinc deficiency

Answer

Iron deficiency

Answer

Calcium deficiency

Answer

Copper deficiency

Question 2

Which of the following statements is FALSE regarding trans fatty acids?

Accepted Answer

The process of hydrogenation decreases the amount of trans fatty acids.

Answer

Increase the risk of cardiovascular disease.

Answer

Fried foods often have a high content of trans fatty acids.

Answer

The process of hydrogenation increases the amount of trans fatty acids.

Question 3

What is the approximate total body iodine content?

Accepted Answer

50 mg

Answer

20 mg

Answer

30 mg

Answer

40 mg

Question 4

Which of the following laboratory values is NOT typically monitored in patients at risk for refeeding syndrome?

Accepted Answer

Ammonium

Answer

Calcium

Answer

Magnesium

Answer

Phosphate

Question 5

What is the best indicator of protein quality?

Accepted Answer

Digestible Indispensable Amino Acid Score (DIAAS)

Answer

Amino acid score

Answer

Protein Digestibility Corrected Amino Acid Score (PDCAAS)

Answer

Protein efficiency ratio

Nutrition and Metabolism — MCQs

Nutrition and Metabolism — MCQs

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