Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 241: Which food item contains the maximum cholesterol content?

A. Egg (Correct Answer)
B. Coconut Oil
C. Hydrogenated Fats
D. Ghee

Explanation: ### Explanation **Correct Option: A (Egg)** The fundamental biochemical principle here is that **cholesterol is exclusively found in animal tissues**. It is a structural component of animal cell membranes and a precursor for steroid hormones. Among the given options, a whole egg (specifically the yolk) contains the highest concentration of cholesterol, approximately **200–250 mg per egg**. In the context of NEET-PG, remember that organ meats (liver, brain) and egg yolks are the richest dietary sources of cholesterol. **Analysis of Incorrect Options:** * **B. Coconut Oil:** This is a plant-derived fat. Plants do not synthesize cholesterol; instead, they contain **phytosterols** (like sitosterol). While coconut oil is high in saturated fatty acids (which can increase endogenous LDL synthesis), it contains zero dietary cholesterol. * **C. Hydrogenated Fats:** These are vegetable oils chemically altered to become solid at room temperature. They are notorious for containing **Trans-fatty acids**, which are highly atherogenic, but they do not contain cholesterol. * **D. Ghee:** Ghee is clarified butter (animal-derived) and does contain cholesterol (approx. 250–300 mg per 100g). However, when comparing standard serving sizes or concentration per unit, a single egg yolk provides a much more concentrated dose of cholesterol than a typical serving of ghee. **High-Yield Clinical Pearls for NEET-PG:** 1. **Plant Sterols:** Sitosterol and Campesterol compete with cholesterol for absorption in the intestine. 2. **Rate-limiting Enzyme:** HMG-CoA Reductase is the key enzyme for endogenous cholesterol synthesis (target of Statins). 3. **Daily Limit:** Traditional guidelines suggest limiting dietary cholesterol to <300 mg/day for healthy individuals. 4. **Transport:** Cholesterol is transported in the blood via lipoproteins (LDL is the primary carrier to tissues; HDL is for reverse transport).

Question 242: The estimation of 3-methyl histidine in urine is used to study:

A. Status of folate in the body
B. Renal disease
C. Skeletal muscle mass (Correct Answer)
D. Protein absorption in the gut

Explanation: **Explanation:** **3-methylhistidine (3-MH)** is a unique amino acid derivative formed by the post-translational methylation of histidine residues specifically within the myofibrillar proteins **actin and myosin**. 1. **Why Skeletal Muscle Mass is Correct:** When skeletal muscle proteins are degraded (proteolysis), 3-methylhistidine is released into the systemic circulation. Unlike other amino acids, 3-MH cannot be reutilized for protein synthesis or further metabolized; it is excreted unchanged in the urine. Therefore, the urinary excretion rate of 3-methylhistidine serves as a reliable biochemical marker for **skeletal muscle mass** and the rate of **muscle protein breakdown**. 2. **Why Other Options are Incorrect:** * **Status of Folate:** Folate status is typically assessed via serum folate, RBC folate, or the **FIGLU (Formiminoglutamic acid) excretion test**. * **Renal Disease:** While 3-MH is excreted by the kidneys, it is a marker of muscle turnover, not a primary diagnostic tool for renal function (where Creatinine or Urea are used). * **Protein Absorption:** Protein absorption is usually evaluated through fecal nitrogen studies or D-xylose tests (for general malabsorption), not specific methylated amino acids. **High-Yield Clinical Pearls for NEET-PG:** * **Actin and Myosin:** 3-MH is found in both, but since skeletal muscle contains the largest pool of these proteins in the body, it dominates the urinary output. * **Dietary Interference:** For accurate results, patients must be on a **meat-free diet** for 3 days prior to the test, as meat consumption contains exogenous 3-MH. * **Negative Nitrogen Balance:** Increased urinary 3-MH is seen in hypercatabolic states like sepsis, major trauma, or starvation, indicating rapid muscle wasting.

Question 243: When milk is taken before a meal, which of the following elements' absorption is decreased?

A. Calcium
B. Iron (Correct Answer)
C. Phosphorous
D. Magnesium

Explanation: **Explanation:** The correct answer is **Iron (B)**. This is a classic high-yield concept in nutrition biochemistry involving nutrient-nutrient interaction. **Why Iron is the correct answer:** Milk is a rich source of **calcium** and **casein** (phosphoprotein). Calcium is a potent inhibitor of both heme and non-heme iron absorption. It interferes with the transport of iron across the intestinal mucosal cells, likely by competing for transport proteins or affecting the expression of ferroportin. Clinical guidelines generally advise against consuming milk or calcium supplements simultaneously with iron-rich meals or iron supplements to prevent iron deficiency anemia. **Why other options are incorrect:** * **Calcium (A):** Taking milk before a meal does not decrease calcium absorption; in fact, milk is the primary vehicle for calcium delivery. Lactose in milk actually *enhances* calcium absorption by creating an acidic environment in the gut. * **Phosphorous (C):** Milk is high in phosphorus. While high phosphorus can theoretically bind calcium, it does not significantly inhibit its own absorption or the absorption of other minerals in this context. * **Magnesium (D):** While calcium and magnesium can compete for the same transporters at very high pharmacological doses, the calcium in a standard serving of milk does not significantly impair dietary magnesium absorption. **High-Yield NEET-PG Pearls:** * **Enhancers of Iron Absorption:** Vitamin C (Ascorbic acid) reduces $Fe^{3+}$ to $Fe^{2+}$, which is more soluble and easily absorbed. Gastric HCl also aids absorption. * **Inhibitors of Iron Absorption:** Phytates (cereals), Oxalates (spinach), Tannins (tea/coffee), and Calcium (milk). * **Milk Anemia:** A common pediatric condition where excessive cow's milk intake leads to iron deficiency due to low iron content in milk and the inhibition of other dietary iron sources.

Question 244: Which of the following substances enhances the absorption of iron?

A. Tea
B. Coffee
C. Vitamin C (Correct Answer)
D. EDTA

Explanation: ### Explanation **Correct Option: C (Vitamin C / Ascorbic Acid)** Iron is primarily absorbed in the duodenum and upper jejunum. Dietary iron exists in two forms: **Heme iron** (from animal sources) and **Non-heme iron** (from plant sources). Non-heme iron is usually in the **Ferric state (Fe³⁺)**, which is insoluble and cannot be absorbed. **Vitamin C (Ascorbic Acid)** enhances absorption via two mechanisms: 1. It acts as a reducing agent, converting insoluble **Ferric (Fe³⁺)** iron into the soluble **Ferrous (Fe²⁺)** state. 2. It forms a soluble chelate with iron, preventing it from precipitating in the alkaline environment of the small intestine. **Incorrect Options:** * **A & B (Tea and Coffee):** These contain **tannins** and **polyphenols** which bind to iron, forming insoluble complexes that inhibit absorption. * **D (EDTA):** Ethylenediaminetetraacetic acid is a potent chelating agent used in food preservation. It binds tightly to iron, making it unavailable for uptake by the intestinal mucosa. **NEET-PG High-Yield Pearls:** * **Promoters of Iron Absorption:** Vitamin C, Gastric Acid (HCl), Amino acids (Cysteine), and "Meat Factor." * **Inhibitors of Iron Absorption:** Phytates (cereals), Oxalates (spinach), Phosphates, Calcium, Carbonates, and Tannins (tea/coffee). * **Transporters:** **DMT-1** (Divalent Metal Transporter 1) transports Fe²⁺ into the enterocyte. **Ferroportin** is the basal exporter that releases iron into the blood. * **Hepcidin:** The master regulator of iron; it inhibits absorption by degrading Ferroportin. High hepcidin levels (seen in chronic inflammation) lead to anemia.

Question 245: Which of the following oils has the highest content of linoleic acid?

A. Sunflower oil
B. Soyabean oil
C. Safflower oil (Correct Answer)
D. Corn oil

Explanation: ### Explanation **Correct Answer: C. Safflower oil** **1. Why Safflower oil is correct:** Linoleic acid (18:2, ω-6) is an **essential fatty acid** (EFA) that the human body cannot synthesize. Among all common dietary vegetable oils, **Safflower oil** contains the highest concentration of linoleic acid, typically ranging from **70% to 75%**. In medical biochemistry and nutrition, it is considered the "gold standard" source for this polyunsaturated fatty acid (PUFA). **2. Analysis of Incorrect Options:** * **A. Sunflower oil:** While very high in PUFAs, it typically contains about **60-65%** linoleic acid. It is a close second but remains lower than safflower oil. * **B. Soyabean oil:** This oil contains approximately **50-55%** linoleic acid. It is also notable for containing about 7-8% alpha-linolenic acid (an ω-3 fatty acid), making it more "balanced" but less concentrated in linoleic acid. * **C. Corn oil:** This contains roughly **55-60%** linoleic acid, similar to soybean oil but slightly higher, yet still significantly lower than safflower oil. **3. High-Yield Clinical Pearls for NEET-PG:** * **Essential Fatty Acids (EFAs):** Linoleic acid (ω-6) and Linolenic acid (ω-3) are essential. Arachidonic acid becomes essential only if linoleic acid is deficient in the diet. * **Phrynoderma (Toad Skin):** Deficiency of EFAs leads to follicular hyperkeratosis, particularly on the extensor surfaces of the body. * **P/S Ratio:** Safflower oil has a very high Polyunsaturated to Saturated (P/S) ratio, which is beneficial for lowering serum cholesterol levels. * **Order of Linoleic Acid Content:** Safflower oil (>70%) > Sunflower oil (~65%) > Corn oil (~60%) > Soyabean oil (~55%) > Groundnut oil (~25%).

Question 246: Which of the following minerals can induce the synthesis of metallothionein?

A. Zinc (Correct Answer)
B. Calcium
C. Iron
D. Phosphorous

Explanation: **Explanation:** **Metallothioneins (MTs)** are a family of low-molecular-weight, cysteine-rich proteins that play a vital role in metal homeostasis and detoxification. 1. **Why Zinc is Correct:** Zinc is the primary physiological inducer of metallothionein synthesis. When intracellular zinc levels rise, zinc ions bind to the **Metal-responsive Transcription Factor-1 (MTF-1)**. This complex then binds to **Metal Response Elements (MRE)** in the promoter region of the metallothionein gene, stimulating its transcription. Metallothionein acts as a "buffer" by sequestering excess free zinc, regulating its bioavailability, and preventing toxicity. 2. **Why Other Options are Incorrect:** * **Calcium:** Calcium levels are regulated by hormones like PTH, Vitamin D, and Calcitonin, primarily through bone remodeling and renal excretion, not metallothionein. * **Iron:** Iron homeostasis is managed by proteins like **Ferritin** (storage) and **Transferrin** (transport). Its synthesis is regulated by Iron Response Elements (IRE) and Iron Regulatory Proteins (IRP). * **Phosphorous:** Phosphorus levels are regulated by the kidneys and FGF-23; it does not interact with metallothionein. **High-Yield Clinical Pearls for NEET-PG:** * **Zinc-Copper Interaction:** High doses of Zinc induce metallothionein in intestinal mucosal cells. Metallothionein has a higher affinity for **Copper** than Zinc. Consequently, Copper becomes trapped within the mucosal cells and is sloughed off, leading to **secondary Copper deficiency**. This principle is used therapeutically in treating **Wilson’s Disease**. * **Detoxification:** Besides Zinc and Copper, metallothionein also binds and detoxifies heavy metals like **Cadmium and Mercury**. * **Antioxidant Role:** Due to its high cysteine content, metallothionein also acts as a scavenger for free radicals.

Question 247: What is the predominant type of whey protein in cow milk?

A. Lactoglobulin (Correct Answer)
B. Lactalbumin
C. Lactoferrin
D. None of the above

Explanation: **Explanation:** Milk proteins are broadly classified into two categories: **Casein** (80%) and **Whey** (20%). Whey protein is the liquid byproduct of cheese production and contains several globular proteins. **1. Why Lactoglobulin is Correct:** The predominant whey protein in cow’s milk is **Beta-lactoglobulin** (approximately 50–55% of total whey). It is a major source of essential and branched-chain amino acids (BCAAs). Notably, Beta-lactoglobulin is absent in human breast milk, which makes it a common allergen in infants (Cow’s Milk Protein Allergy). **2. Analysis of Incorrect Options:** * **Lactalbumin (Alpha-lactalbumin):** This is the second most abundant whey protein in cow’s milk (approx. 20–25%). However, it is the **predominant** whey protein in **human milk**. It plays a crucial role in lactose synthesis. * **Lactoferrin:** This is a minor whey protein known for its iron-binding properties and antimicrobial effects. While highly significant in colostrum and human milk for infant immunity, its concentration in cow’s milk is very low. **3. High-Yield Clinical Pearls for NEET-PG:** * **Casein vs. Whey Ratio:** Cow’s milk is Casein-dominant (80:20), whereas Human milk is Whey-dominant (40:60). * **The "Absent" Protein:** Beta-lactoglobulin is present in cow's milk but **absent in human milk**. This is a frequent MCQ point regarding infant formula sensitivity. * **Lactose Synthesis:** Alpha-lactalbumin acts as a regulatory subunit for the enzyme *lactose synthase*. * **Biological Value:** Whey protein has a higher biological value (BV) than casein due to its rapid digestion and high leucine content.

Question 248: Which of the following statements is true about Net Protein Utilization (NPU)?

A. It is the ratio of energy from protein to total energy in diet.
B. It is the ratio of total nitrogen retained to total nitrogen intake, multiplied by 100. (Correct Answer)
C. It is the amount of one amino acid per gram of a protein divided by the amount of the same amino acid per gram of egg protein.
D. A high NPU indicates a need for increased protein intake.

Explanation: **Explanation:** Net Protein Utilization (NPU) is a key indicator of the nutritional quality of a protein. It measures how much of the nitrogen consumed is actually retained by the body for growth and maintenance. **Why Option B is Correct:** NPU is mathematically defined as: $$\text{NPU} = \frac{\text{Nitrogen Retained}}{\text{Nitrogen Intake}} \times 100$$ It is a superior measure to Biological Value (BV) because it accounts for **digestibility**. While BV only measures the nitrogen retained from what is *absorbed*, NPU measures the nitrogen retained from what is *eaten*. The relationship is: $\text{NPU} = \text{Biological Value} \times \text{Digestibility Coefficient}$. **Analysis of Incorrect Options:** * **Option A:** This describes the **Protein Energy Ratio (PE ratio)**, which evaluates the protein density of a diet rather than its quality. * **Option C:** This describes the **Chemical Score** (or Amino Acid Score), which compares the limiting amino acid of a test protein to a reference protein (usually egg protein). * **Option D:** A high NPU indicates that the protein is of **high quality** (like egg or milk protein) and is being used efficiently; therefore, a *lower* total intake is required to meet nutritional needs. **High-Yield Clinical Pearls for NEET-PG:** * **Reference Protein:** Egg protein is considered the "Gold Standard" with an NPU and Biological Value of approximately **100**. * **Limiting Amino Acids:** Pulses are deficient in Methionine; Cereals are deficient in Lysine. * **Mutual Supplementation:** Consuming cereals and pulses together improves the overall NPU of a vegetarian diet. * **NPU of common foods:** Egg (100) > Milk (75) > Meat (72) > Rice (65) > Wheat (49) > Bengal Gram (47).

Question 249: Which of the following foods can a patient with gluten hypersensitivity consume?

A. Rice (Correct Answer)
B. Barley
C. Oats
D. Corn

Explanation: **Explanation:** Gluten hypersensitivity, most notably **Celiac Disease**, is an autoimmune-mediated enteropathy triggered by the ingestion of **prolamins** (gluten proteins) in genetically susceptible individuals. The management revolves around a strict lifelong gluten-free diet. **Why Rice is the Correct Answer:** Rice is naturally gluten-free. The storage proteins in rice (oryzenin) do not contain the specific amino acid sequences (rich in proline and glutamine) that trigger the inflammatory T-cell response seen in Celiac disease. Therefore, rice, along with maize (corn), sorghum, and millets, are safe staples for these patients. **Analysis of Other Options:** * **Barley (Option B):** Contains the prolamin **Hordein**, which is highly toxic to patients with gluten hypersensitivity. * **Oats (Option C):** Contain **Avenin**. While some patients tolerate pure oats, most commercial oats are cross-contaminated with wheat during processing. In the context of standard medical exams, oats are generally excluded from a gluten-free diet unless specified as "certified gluten-free." * **Corn (Option D):** While corn is technically gluten-free, **Rice** is the most classically cited "safe" grain in biochemistry and pediatrics modules for this condition. *Note: In many clinical scenarios, both Rice and Corn are safe; however, if forced to choose the "most" standard answer in a single-choice format, Rice is the gold standard.* **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic (BROW):** Avoid **B**arley, **R**ye, **O**ats, and **W**heat. * **Toxic Prolamins:** Wheat (**Gliadin**), Barley (**Hordein**), Rye (**Secalin**). * **Diagnosis:** Gold standard is a **Duodenal Biopsy** showing villous atrophy, crypt hyperplasia, and increased intraepithelial lymphocytes. * **Serology:** Anti-tissue Transglutaminase (**anti-tTG**) IgA is the screening drug of choice. * **HLA Association:** Strongly linked with **HLA-DQ2** and **HLA-DQ8**.

Question 250: Which of the following trace elements is important for the conversion of procollagen to collagen?

A. Selenium (Se)
B. Copper (Cu) (Correct Answer)
C. Zinc (Zn)
D. Magnesium (Mg)

Explanation: **Explanation:** The correct answer is **Copper (Cu)**. The conversion of procollagen to mature collagen requires the extracellular cross-linking of tropocollagen units. This process is catalyzed by the enzyme **Lysyl Oxidase**, which is a **copper-dependent enzyme**. Lysyl oxidase oxidatively deaminates specific lysine and hydroxylysine residues to form reactive aldehydes (allysine). These aldehydes then undergo spontaneous covalent bonding to form the stable cross-links that provide collagen with its high tensile strength. **Analysis of Incorrect Options:** * **Selenium (Se):** It is a vital component of **Glutathione Peroxidase**, an antioxidant enzyme that protects cells from oxidative damage. It is not involved in collagen synthesis. * **Zinc (Zn):** While Zinc is essential for wound healing, it acts as a cofactor for **Matrix Metalloproteinases (MMPs)** involved in collagen remodeling and degradation, rather than the initial cross-linking. It is also a cofactor for Carbonic Anhydrase and Alkaline Phosphatase. * **Magnesium (Mg):** It acts as a cofactor for over 300 enzymes, particularly those involving **ATP utilization** (kinases) and DNA/RNA synthesis, but it does not play a direct role in collagen maturation. **High-Yield Clinical Pearls for NEET-PG:** * **Menkes Disease:** An X-linked recessive disorder caused by impaired copper absorption (ATP7A mutation). This leads to deficient Lysyl Oxidase activity, resulting in "kinky" hair, connective tissue defects, and skeletal abnormalities. * **Vitamin C (Ascorbate):** Do not confuse cross-linking with **hydroxylation**. Vitamin C is required for the hydroxylation of proline and lysine residues *inside* the cell; deficiency leads to Scurvy. * **Scurvy vs. Menkes:** Scurvy is a defect in *hydroxylation* (Vitamin C), while Menkes is a defect in *cross-linking* (Copper).

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

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Functional Foods and Nutraceuticals

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Dietary Guidelines and Recommendations

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