Nutrition and Metabolism Practice Questions

Q: 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?

Zinc deficiency. **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.

Q: Which of the following is a trace element required for human nutrition?

Zinc (Zn). ***Zinc (Zn)*** - Classified as a **trace element** with daily requirement of approximately **8-11 mg/day** (<100 mg/day threshold). - Functions as a **cofactor** for over 300 enzymes including **carbonic anhydrase**, **alcohol dehydrogenase**, and **DNA/RNA polymerases**. *Magnesium (Mg)* - A **macro-mineral** required in amounts of **300-400 mg/day**, well above the trace element threshold. - Essential for **ATP-related reactions** and **bone structure**, but not classified as a trace element. *Calcium (Ca)* - The most abundant mineral in the body and a **macro-mineral** with RDA of approximately **1000 mg/day**. - Primary role in **bone mineralization** and **muscle contraction**, requiring much higher daily intake than trace elements. *Potassium (K)* - A **macro-mineral** with very high daily requirement of **3500-4700 mg/day** to maintain **membrane potential**. - Functions as the primary **intracellular cation**, requiring amounts far exceeding trace element classification.

Q: Which protein is known as the reference protein?

Milk. **Explanation:** The concept of a **Reference Protein** refers to a protein that contains all essential amino acids in the optimal proportions required by the human body for growth and maintenance. **Why Milk is the Correct Answer:** In nutritional biochemistry, **Milk protein (specifically Egg protein and Milk protein)** is considered a reference protein because it has a high biological value (BV) and a Net Protein Utilization (NPU) score near 100. These proteins are almost completely absorbed and utilized by the body. While Egg is often cited as the "gold standard" reference protein in many textbooks, **Milk** is the correct choice among the given options as it provides a complete amino acid profile with high bioavailability. **Analysis of Incorrect Options:** * **B. Soyabean:** Although it is the richest plant source of protein, it is deficient in sulfur-containing amino acids like **Methionine**. Plant proteins are generally "incomplete" compared to animal sources. * **C. Orange:** Oranges are primarily a source of Vitamin C and carbohydrates; their protein content is negligible. * **D. Potato:** While potatoes contain high-quality protein (Tuberin), the total quantity is too low (approx. 2%) to serve as a primary reference source. **High-Yield NEET-PG Pearls:** * **Biological Value (BV):** Measures the proportion of absorbed protein retained in the body. Egg has a BV of 100. * **Limiting Amino Acids:** Pulses are deficient in **Methionine**, while Cereals are deficient in **Lysine**. * **Mutual Supplementation:** Combining cereals and pulses (e.g., Khichdi) provides a complete amino acid profile, a concept frequently tested in community medicine and biochemistry. * **Reference Protein Standard:** The FAO/WHO often uses the amino acid composition of **Egg or Milk** as the benchmark to calculate the "Chemical Score" of other foods.

Q: What is the major mineral component of bone?

Hydroxyapatite. **Explanation:** The correct answer is **Hydroxyapatite**. Bone is a specialized connective tissue consisting of an organic matrix (primarily Type I collagen) and an inorganic mineral phase. The mineral component accounts for approximately 65-70% of bone weight and is primarily composed of a crystalline form of calcium phosphate known as **Hydroxyapatite**, with the chemical formula **$\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2$**. These crystals align along collagen fibers to provide the skeleton with its characteristic compressive strength and structural rigidity. **Analysis of Options:** * **Calcite (A):** This is a stable polymorph of calcium carbonate found in the shells of marine organisms and limestone, but it is not a biological component of human bone. * **Calcium oxide (C):** Also known as quicklime, this is a caustic chemical used in industrial processes. It does not occur naturally in human tissues. * **Calcium carbonate (D):** While small amounts of carbonate are incorporated into the hydroxyapatite lattice as impurities, pure calcium carbonate is the primary component of eggshells and antacid tablets, not the structural mineral of bone. **High-Yield Clinical Pearls for NEET-PG:** * **Mineralization:** The process of depositing hydroxyapatite into the organic matrix is regulated by **alkaline phosphatase**, which increases local phosphate concentrations. * **Fluorosis:** Fluoride ions can replace the hydroxyl (-OH) groups in hydroxyapatite to form **Fluoroapatite**, which is more resistant to acid dissolution (relevant in dental caries prevention). * **Vitamin D:** Essential for bone health as it maintains the calcium-phosphorus product necessary for the crystallization of hydroxyapatite. * **Bone Reservoir:** Hydroxyapatite serves as the body’s primary reservoir for calcium (99%) and phosphorus (85%).

Q: In marasmus, wasting is due to which of the following?

All of the above. **Explanation:** Marasmus is a form of severe protein-energy malnutrition (PEM) characterized by a global deficiency of nutrients. The underlying pathophysiology involves a state of negative energy balance where the body adapts to starvation. 1. **Why Option D is correct:** Marasmus results from a **prolonged deficiency of both calories (energy) and protein (Option A & B)**. Unlike Kwashiorkor, where protein deficiency is disproportionately greater than calorie intake, Marasmus is "balanced" starvation. To compensate for the lack of exogenous fuel, the body enters a hypercatabolic state. It mobilizes endogenous stores, leading to the **excess catabolism of subcutaneous fat and skeletal muscle (Option C)** to provide amino acids for gluconeogenesis and fatty acids for energy. This results in the characteristic "skin and bones" appearance. 2. **Analysis of Options:** * **Option A & B:** These are the primary triggers. While Kwashiorkor is classically "Protein deficiency with adequate calories," Marasmus is "Total calorie deficiency." * **Option C:** This is the physiological mechanism of wasting. The body sacrifices muscle mass to maintain blood glucose levels for vital organ function. **High-Yield Clinical Pearls for NEET-PG:** * **Appearance:** "Old man's face" or "Monkey-like facies" due to loss of buccal pads of fat. * **Edema:** Absent in Marasmus (present in Kwashiorkor due to hypoalbuminemia). * **Growth:** Severe growth retardation and "baggy pants" appearance (loose skin folds over buttocks). * **Key Difference:** Marasmus = Starvation (Calorie + Protein); Kwashiorkor = Protein deficiency + Stress/Infection.

Q: A patient receiving total parenteral nutrition is at risk of developing which of the following nutrient deficiencies?

Zinc. **Explanation:** **Correct Option: D (Zinc)** Patients on Total Parenteral Nutrition (TPN) are at a high risk of trace element deficiencies, most notably **Zinc**. Zinc is primarily absorbed in the small intestine; in TPN patients, the bypass of the gastrointestinal tract, coupled with increased urinary losses and high metabolic demands, leads to rapid depletion. * **Clinical Presentation:** Zinc deficiency in TPN patients typically manifests as **acrodermatitis enteropathica-like lesions** (periorificial and acral dermatitis), alopecia, impaired wound healing, and altered taste (hypogeusia). **Why Incorrect Options are Wrong:** * **A & B (Vitamin B12 and Folic Acid):** These are water-soluble vitamins that are standard components of routine parenteral multivitamin formulations (e.g., MVI-12). While B12 stores in the liver can last for years, folate stores last for months; however, acute deficiency is rare in TPN unless they are omitted from the daily infusion. * **C (Vitamin B6):** Pyridoxine is also routinely supplemented in TPN solutions. Isolated deficiency is uncommon compared to the rapid onset of trace element depletion like Zinc. **NEET-PG High-Yield Pearls:** * **Most common trace element deficiency in TPN:** Zinc. * **Chromium deficiency in TPN:** Presents as **glucose intolerance** (insulin resistance) because chromium is a component of the Glucose Tolerance Factor. * **Copper deficiency in TPN:** Presents as microcytic anemia and neutropenia (resembling Vitamin B12 deficiency but with normal B12 levels). * **Selenium deficiency in TPN:** Can lead to **cardiomyopathy** (Keshan-like disease) and muscle pain.

Q: Which amino acid is considered limiting in soybeans?

Methionine. ### 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.

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

Lysine. ### 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)

Q: Maize is deficient in which amino acid?

Tryptophan. **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).

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

Lignin. **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 1

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?

Accepted Answer

Zinc deficiency

Answer

Copper deficiency

Answer

Chromium deficiency

Answer

Manganese deficiency

Question 2

Which of the following is a trace element required for human nutrition?

Accepted Answer

Zinc (Zn)

Answer

Magnesium (Mg)

Answer

Calcium (Ca)

Answer

Potassium (K)

Question 3

Which protein is known as the reference protein?

Accepted Answer

Milk

Answer

Soyabean

Answer

Orange

Answer

Potato

Question 4

What is the major mineral component of bone?

Accepted Answer

Hydroxyapatite

Answer

Calcite

Answer

Calcium oxide

Answer

Calcium carbonate

Question 5

In marasmus, wasting is due to which of the following?

Accepted Answer

All of the above

Answer

Prolonged dietary deficiency of calories

Answer

Prolonged dietary deficiency of protein

Answer

Excess catabolism of fat and muscle mass to provide energy

Question 6

A patient receiving total parenteral nutrition is at risk of developing which of the following nutrient deficiencies?

Accepted Answer

Zinc

Answer

Vitamin B12

Answer

Folic acid

Answer

Vitamin B6

Question 7

Which amino acid is considered limiting in soybeans?

Accepted Answer

Methionine

Answer

Threonine

Answer

Lysine

Answer

Tryptophan

Question 8

Maize is deficient in which of the following amino acids?

Accepted Answer

Lysine

Answer

Methionine

Answer

Leucine

Answer

All of the above

Question 9

Maize is deficient in which amino acid?

Accepted Answer

Tryptophan

Answer

Leucine

Answer

Methionine

Answer

Phenylalanine

Question 10

Which of the following is not degraded by colonic flora?

Accepted Answer

Lignin

Answer

Pectin

Answer

Starch

Answer

Glucose

Nutrition and Metabolism — MCQs

Nutrition and Metabolism — MCQs

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