Nutrition and Metabolism Practice Questions

Q: Which amino acid is deficient in pulses?

Methionine. **Explanation:** In nutritional biochemistry, proteins are classified as "complete" or "incomplete" based on their essential amino acid profile. Most plant-based proteins are incomplete as they lack one or more essential amino acids, known as the **limiting amino acid**. **1. Why Methionine is the correct answer:** Pulses (legumes) are rich in lysine but are characteristically deficient in **sulfur-containing amino acids**, primarily **Methionine** and Cysteine. This is why a diet based solely on pulses cannot meet the body's total protein requirements for growth and repair. **2. Analysis of Incorrect Options:** * **Tryptophan (A):** This is the limiting amino acid in **Maize (Corn)**. A deficiency of tryptophan leads to Pellagra because tryptophan is a precursor for Niacin (Vitamin B3) synthesis. * **Lysine (B):** This is the limiting amino acid in **Cereals** (wheat, rice, maize). Interestingly, pulses are an excellent source of lysine, which is why the "cereal-pulse combination" (e.g., rice and dal) provides a complete amino acid profile. * **Leucine (D):** This is found in high amounts in **Sorghum (Jowar)**. An excess of leucine can interfere with tryptophan metabolism, potentially precipitating Pellagra. **High-Yield Clinical Pearls for NEET-PG:** * **Mutual Supplementation:** Combining cereals (deficient in lysine, rich in methionine) with pulses (deficient in methionine, rich in lysine) creates a **Complementary Protein** effect. * **Limiting Amino Acid Summary:** * **Pulses:** Methionine * **Cereals:** Lysine * **Maize:** Tryptophan and Lysine * **Reference Protein:** Egg protein is considered the "standard" or "complete" protein (Biological Value = 100) against which others are compared.

Q: What is the best index for calculating the nutritional value of protein?

Net protein utilization. ### Explanation The nutritional value of a protein depends on two factors: its amino acid composition and its digestibility. **Why Net Protein Utilization (NPU) is the best index:** NPU is considered the most comprehensive index because it accounts for both the **quality** (amino acid profile) and the **digestibility** of the protein. It is calculated as the percentage of ingested nitrogen that is retained in the body. * **Formula:** $NPU = \text{Biological Value (BV)} \times \text{Digestibility Coefficient}$. By incorporating digestibility, NPU provides a more accurate reflection of how much protein is actually available for metabolic use compared to Biological Value alone. **Analysis of Incorrect Options:** * **A. Biological Value (BV):** This measures the percentage of *absorbed* nitrogen retained by the body. While it assesses protein quality, it ignores the fraction of protein lost during digestion (fecal loss). * **C. Protein Digestibility:** This only measures how much of the ingested protein is absorbed into the bloodstream. It does not account for the essential amino acid balance or how well the body utilizes the absorbed protein. * **D. Protein Efficiency Ratio (PER):** This is the gain in body weight per gram of protein ingested (usually measured in rats). It is flawed because it assumes all weight gain is muscle/protein and does not account for maintenance needs. **High-Yield Clinical Pearls for NEET-PG:** * **Reference Protein:** Egg protein (Albumin) is the gold standard with a BV and NPU of approximately 100. * **Limiting Amino Acids:** Pulses are deficient in Methionine; Cereals are deficient in Lysine. * **PDCAAS (Protein Digestibility Corrected Amino Acid Score):** Currently the internationally "preferred" method for evaluating protein quality in human nutrition, though NPU remains the best traditional biological index.

Q: Metabolism of 100 grams of fat yields approximately how many kilocalories?

900. **Explanation:** The correct answer is **D (900)**. This is based on the physiological fuel values of macronutrients, which represent the amount of energy available to the body after digestion and absorption. 1. **Why 900 is correct:** Fat is the most energy-dense macronutrient. The standard physiological fuel value for fat is **9 kcal/gram**. Therefore, the metabolism of 100 grams of fat yields: * $100 \text{ g} \times 9 \text{ kcal/g} = \mathbf{900 \text{ kcal}}$. Fats provide more than double the energy of carbohydrates or proteins because they are more reduced (contain more carbon-hydrogen bonds), requiring more oxidation to produce $CO_2$ and $H_2O$. 2. **Why other options are incorrect:** * **Option B (400):** This represents the energy yield of 100 grams of **Carbohydrates** or **Proteins**. Both yield approximately **4 kcal/gram** ($100 \times 4 = 400$). * **Options A and C (200 and 600):** These values do not correspond to the standard metabolism of any single primary macronutrient in these quantities. **High-Yield Clinical Pearls for NEET-PG:** * **Respiratory Quotient (RQ):** Fat has an RQ of **0.7**, which is lower than carbohydrates (1.0) because fat requires more oxygen for its oxidation. * **Specific Dynamic Action (SDA):** Also known as the Thermic Effect of Food. Protein has the highest SDA (~30%), followed by carbohydrates (5–10%) and fats (0–3%). * **Energy Storage:** Fat is stored in anhydrous form in adipose tissue, making it the most efficient long-term energy reservoir in the human body. * **Alcohol:** Yields **7 kcal/gram**, placing its energy density between carbohydrates and fats.

Q: Rice is deficient in which essential amino acid?

Threonine. **Explanation:** In nutritional biochemistry, cereals and pulses are characterized by their "limiting amino acids"—the essential amino acids present in the shortest supply relative to human requirements. **Why Threonine is correct:** While most medical textbooks traditionally emphasize **Lysine** as the primary limiting amino acid in all cereals (including rice, wheat, and maize), **Threonine** is recognized as the **second limiting amino acid** in rice. In many competitive exams like NEET-PG, when Lysine is not provided in the options, Threonine is the established correct answer for rice deficiency. **Analysis of Incorrect Options:** * **Serine:** This is a non-essential amino acid synthesized from 3-phosphoglycerate; it is not a limiting factor in dietary proteins. * **Methionine & Cysteine:** These are sulfur-containing amino acids. While they are the limiting amino acids in **pulses/legumes**, they are generally present in adequate amounts in cereals like rice. **High-Yield Clinical Pearls for NEET-PG:** * **Cereals (Rice/Wheat):** Deficient in Lysine (1st) and Threonine (2nd). * **Pulses (Legumes):** Deficient in Methionine and Cysteine. * **Maize (Corn):** Deficient in Lysine and **Tryptophan**. (Note: Tryptophan deficiency in maize leads to Pellagra because it is a precursor for Niacin/Vitamin B3). * **Mutual Supplementation:** This is the nutritional strategy of combining cereals and pulses (e.g., Rice and Dal) to provide a complete amino acid profile, as the deficiency of one is compensated by the other.

Q: All of the following conditions will have a hypermetabolic state except:

Anorexia nervosa. **Explanation:** The metabolic state of the body is determined by the **Basal Metabolic Rate (BMR)**. A **hypermetabolic state** is characterized by an increased BMR, usually triggered by systemic inflammation, severe stress, or hormonal imbalances. Conversely, a **hypometabolic state** occurs when the body attempts to conserve energy during periods of prolonged starvation or nutrient deficiency. **Why Anorexia Nervosa is the Correct Answer:** In **Anorexia Nervosa** and **Protein-Energy Malnutrition (PEM)**, the body undergoes an adaptive response to chronic starvation. To preserve vital organ function and survive on limited caloric intake, the body lowers its BMR, leading to a **hypometabolic state**. This is often clinically manifested as bradycardia, hypotension, and hypothermia. *Note: While the question asks for the "except," both PEM and Anorexia Nervosa are technically hypometabolic. However, in competitive exams like NEET-PG, Anorexia Nervosa is the classic prototype for a psychiatric-driven hypometabolic state, whereas PEM is a broader nutritional category.* **Why the other options are incorrect:** * **Accident (Trauma) & Burns:** These are classic examples of the **"Flow Phase"** of the metabolic response to injury. The release of catecholamines, cortisol, and inflammatory cytokines (IL-1, IL-6, TNF-α) causes massive mobilization of energy stores, leading to significant **hypermetabolism**. Burns, in particular, can increase BMR by up to 100%. **High-Yield Clinical Pearls for NEET-PG:** * **Highest BMR Increase:** Major burns (up to 2x normal). * **Hormones increasing BMR:** Thyroxine (T4/T3) is the primary regulator; Epinephrine and Cortisol also increase it. * **Specific Dynamic Action (SDA):** Proteins have the highest SDA (30%), meaning they increase metabolic rate more than fats or carbohydrates during digestion. * **Hypometabolic states:** Hypothyroidism, Starvation, Anorexia Nervosa, and PEM.

Q: Calcium absorption is aided by all of the following except?

Fat. **Explanation:** Calcium absorption primarily occurs in the duodenum and jejunum via active transport and passive diffusion. The correct answer is **Fat**, as it generally inhibits rather than aids calcium absorption. **Why Fat is the correct answer:** Excessive or malabsorbed dietary fats react with free calcium in the intestinal lumen to form **insoluble calcium soaps** (steatorrhea). These soaps cannot be absorbed and are excreted in the feces. This is why conditions like Celiac disease or biliary obstruction often lead to secondary calcium deficiency. **Why the other options are incorrect:** * **Vitamin D:** This is the most potent stimulator of calcium absorption. It induces the synthesis of **Calbindin-D**, a transport protein in intestinal mucosal cells that facilitates the uptake of calcium. * **Vitamin C:** Ascorbic acid creates an **acidic environment** in the gut. Calcium is significantly more soluble in an acidic pH, which enhances its absorption. * **Lactose:** Milk sugar (lactose) promotes calcium absorption through two mechanisms: it lowers the luminal pH via fermentation by gut flora and enhances passive diffusion across the intestinal wall. **High-Yield Clinical Pearls for NEET-PG:** * **Inhibitors of Calcium Absorption:** Phytates (cereals), Oxalates (spinach), Phosphates, and high fiber intake. * **Facilitators of Calcium Absorption:** Acidic pH, Vitamin D, Lactose, and certain amino acids (Lysine and Arginine). * **Ratio:** The ideal dietary Calcium to Phosphorus ratio for optimal absorption in infants is **2:1** (as found in breast milk). * **Site:** Active transport of calcium is maximal in the **duodenum**, while the greatest total amount is absorbed in the **jejunum** due to longer transit time.

Q: Which of the following is an exception for the presence of n-3 PUFA?

Groundnut oil. ### Explanation The question focuses on the distribution of **Omega-3 (n-3) Polyunsaturated Fatty Acids (PUFAs)** in dietary sources. Omega-3 fatty acids, such as Alpha-linolenic acid (ALA), Eicosapentaenoic acid (EPA), and Docosahexaenoic acid (DHA), are essential fatty acids characterized by a double bond at the third carbon atom from the methyl (omega) end. **Why Groundnut Oil is the Correct Answer:** Groundnut (Peanut) oil is predominantly composed of **Monounsaturated Fatty Acids (MUFA)**, specifically Oleic acid (~50%), and **n-6 PUFA** (Linoleic acid). It contains **negligible to zero amounts of n-3 PUFA**. Therefore, it stands as the exception among the listed options. **Analysis of Incorrect Options:** * **Mustard Oil:** Unlike many other vegetable oils, mustard oil is a significant plant source of **Alpha-linolenic acid (ALA)**, an n-3 PUFA (approx. 6–10%). * **Corn Oil:** While primarily high in n-6 PUFAs, corn oil contains small but measurable amounts of n-3 PUFAs (approx. 1%). In the context of competitive exams, it is generally categorized as containing n-3, unlike groundnut oil. * **Fish Oil:** This is the richest source of long-chain n-3 PUFAs, specifically **EPA and DHA**, which are vital for cardiovascular health and brain function. **High-Yield NEET-PG Pearls:** * **Essential Fatty Acids:** Linoleic acid (n-6) and Alpha-linolenic acid (n-3) are "essential" because humans lack the enzymes (**$\Delta^{12}$ and $\Delta^{15}$ desaturases**) to create double bonds beyond carbon 9. * **P/S Ratio:** The Polyunsaturated to Saturated fat ratio is a key indicator of dietary quality; the ideal ratio is roughly 0.8 to 1.0. * **Clinical Benefit:** n-3 PUFAs reduce serum triglycerides and inhibit VLDL synthesis, providing cardioprotective effects.

Q: All of the following functions require zinc as a micro-element, EXCEPT?

Melanin synthesis. **Explanation:** Zinc is a vital trace element that acts as a cofactor for over 300 enzymes (Zinc-metalloproteins) and is essential for structural integrity via "zinc finger motifs" in transcription factors. **Why Melanin Synthesis is the Correct Answer:** Melanin synthesis is primarily dependent on the enzyme **Tyrosinase**, which is a **Copper-containing enzyme**, not zinc-dependent. Tyrosinase catalyzes the rate-limiting step of converting Tyrosine to DOPA and subsequently to dopaquinone. Therefore, copper deficiency, rather than zinc deficiency, leads to hypopigmentation. **Analysis of Incorrect Options:** * **Spermatogenesis:** Zinc is highly concentrated in the testes and prostate. It is essential for DNA synthesis, cell division, and the maintenance of the germinal epithelium. Deficiency leads to oligospermia and testicular atrophy. * **Fetal Growth & Embryonic Development:** Zinc is a constituent of RNA and DNA polymerases. It plays a critical role in rapid cell proliferation and gene expression during embryogenesis. Maternal zinc deficiency is strongly linked to congenital malformations (neural tube defects) and intrauterine growth restriction (IUGR). **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder of zinc absorption characterized by periorificial dermatitis, alopecia, and diarrhea. * **Wound Healing:** Zinc is essential for collagen synthesis and fibroblast proliferation; deficiency causes delayed wound healing. * **Gustin:** A zinc-containing protein in saliva required for taste bud development (deficiency causes **hypogeusia**). * **Carbonic Anhydrase & Alcohol Dehydrogenase:** These are classic examples of zinc-dependent enzymes frequently tested in exams.

Q: Which of the following are considered anti-carcinogens?

Carotenoids. **Explanation:** **Correct Answer: A. Carotenoids** **Why it is correct:** Anti-carcinogens are substances that inhibit, delay, or reverse the process of carcinogenesis (cancer formation). **Carotenoids** (such as beta-carotene, lycopene, and lutein) are potent antioxidants. They protect cells from DNA damage by neutralizing free radicals and reactive oxygen species (ROS). Furthermore, they enhance the immune system’s surveillance against tumor cells and induce phase II detoxification enzymes, making them a primary dietary anti-carcinogen. **Analysis of Incorrect Options:** * **B. Flavonoids:** While flavonoids do possess antioxidant properties, in the specific context of standard medical entrance exams and classical biochemistry, **Carotenoids** are the most recognized and frequently cited "dietary anti-carcinogens." Flavonoids are often categorized more broadly as polyphenols. * **C. Curcumoids:** Curcumin (found in turmeric) has anti-inflammatory and anti-cancer properties; however, "Curcumoids" is a less standardized term in this specific MCQ context compared to the established role of Carotenoids. * **D. Benzene:** This is a potent **carcinogen** (specifically a Group 1 carcinogen). Chronic exposure to benzene is strongly associated with the development of Acute Myeloid Leukemia (AML) by causing chromosomal damage in bone marrow. **High-Yield Clinical Pearls for NEET-PG:** * **Other Anti-carcinogens:** Vitamin C, Vitamin E, Selenium, and Isothiocyanates (found in cruciferous vegetables). * **The Beta-Carotene Paradox:** While dietary carotenoids are protective, high-dose *supplemental* beta-carotene has been shown to increase the risk of lung cancer in heavy smokers (CARET study). * **Lycopene:** A specific carotenoid found in tomatoes, highly associated with a reduced risk of **Prostate Cancer**. * **Aflatoxin B1:** A potent carcinogen (from *Aspergillus flavus*) associated with Hepatocellular Carcinoma (HCC).

Question 1

Which amino acid is deficient in pulses?

Accepted Answer

Methionine

Answer

Tryptophan

Answer

Lysine

Answer

Leucine

Question 2

What is the best index for calculating the nutritional value of protein?

Accepted Answer

Net protein utilization

Answer

Biological Value

Answer

Protein digestibility

Answer

Protein efficiency ratio

Question 3

Metabolism of 100 grams of fat yields approximately how many kilocalories?

Accepted Answer

900

Answer

200

Answer

400

Answer

600

Question 4

Rice is deficient in which essential amino acid?

Accepted Answer

Threonine

Answer

Serine

Answer

Methionine

Answer

Cysteine

Question 5

Which of the following correlates well to overcoming of limiting amino acids in the diet?

Accepted Answer

Complementary action of proteins

Answer

Rancidity

Answer

Tertiary structure of proteins

Answer

Biological value

Question 6

All of the following conditions will have a hypermetabolic state except:

Accepted Answer

Anorexia nervosa

Answer

Accident

Answer

Burns

Answer

PEM

Question 7

Calcium absorption is aided by all of the following except?

Accepted Answer

Fat

Answer

Vitamin D

Answer

Vitamin C

Answer

Lactose

Question 8

Which of the following is an exception for the presence of n-3 PUFA?

Accepted Answer

Groundnut oil

Answer

Mustard oil

Answer

Corn oil

Answer

Fish oil

Question 9

All of the following functions require zinc as a micro-element, EXCEPT?

Accepted Answer

Melanin synthesis

Answer

Spermatogenesis

Answer

Fetal growth

Answer

Embryonic development

Question 10

Which of the following are considered anti-carcinogens?

Accepted Answer

Carotenoids

Answer

Flavonoids

Answer

Curcumoids

Answer

Benzene

Nutrition and Metabolism — MCQs

Nutrition and Metabolism — MCQs

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