Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 271: What is the minimum daily intake of iodide?

A. 20 micrograms (Correct Answer)
B. 40 micrograms
C. 60 micrograms
D. 80 micrograms

Explanation: **Explanation:** The thyroid gland requires a steady supply of iodine to synthesize thyroid hormones (T3 and T4). The **minimum daily intake** required to prevent the development of a goiter and maintain normal thyroid function is **20 micrograms**. 1. **Why 20 micrograms is correct:** At this threshold, the thyroid gland's iodide trap (Sodium-Iodide Symporter) can concentrate enough iodine to meet the basal metabolic requirements for hormone synthesis. If intake falls below this level, the thyroid cannot maintain adequate hormone production, leading to increased TSH secretion and subsequent thyroid hypertrophy (goiter). 2. **Why other options are incorrect:** Options B (40 µg), C (60 µg), and D (80 µg) are all above the absolute minimum physiological requirement. While these levels are safer than 20 µg, they do not represent the "minimum" threshold defined in nutritional biochemistry for preventing deficiency symptoms. **Clinical Pearls for NEET-PG:** * **Recommended Dietary Allowance (RDA):** While the *minimum* is 20 µg, the **RDA** for a normal adult is **150 micrograms**. * **Pregnancy/Lactation:** The requirement increases to **220–290 micrograms** to support fetal brain development. * **Wolff-Chaikoff Effect:** An acute, excessive load of iodine can paradoxically inhibit thyroid hormone synthesis. * **Excretion:** Iodine is primarily excreted via the **kidneys** (urinary iodine is a key indicator of a population's iodine status). * **Deficiency:** It is the most common cause of preventable intellectual disability worldwide.

Question 272: Which one of the following is a trace element?

A. Copper (Correct Answer)
B. Sodium
C. Calcium
D. Fats

Explanation: ### Explanation In human nutrition, minerals are classified based on the daily requirement and their concentration in the body. **Trace elements** (or microminerals) are those required in amounts less than **100 mg/day**. **1. Why Copper is the Correct Answer:** Copper is a classic trace element. It serves as an essential cofactor for several "cuproenzymes" critical for metabolism, including **Cytochrome c oxidase** (electron transport chain), **Superoxide dismutase** (antioxidant defense), and **Lysyl oxidase** (collagen cross-linking). Its deficiency leads to Menkes disease, while its toxicity (impaired excretion) causes Wilson’s disease. **2. Analysis of Incorrect Options:** * **Sodium (B) & Calcium (C):** These are **Macro-elements** (principal minerals). They are required in amounts greater than 100 mg/day (often >1000 mg/day). They play structural roles (Calcium in bone) or maintain osmotic balance and nerve impulse conduction (Sodium). * **Fats (D):** These are **Macronutrients**, not minerals. They provide energy (9 kcal/g) and are required in large quantities (grams) as part of a balanced diet. **3. NEET-PG High-Yield Pearls:** * **Essential Trace Elements:** Iron, Zinc, Copper, Manganese, Iodine, Selenium, Molybdenum, and Cobalt. * **Ultra-trace elements:** Required in <1 mg/day (e.g., Chromium, Fluoride). * **Zinc:** Essential for carbonic anhydrase and DNA polymerase; deficiency causes *Acrodermatitis enteropathica*. * **Selenium:** Component of **Glutathione peroxidase**, protecting cells from oxidative damage. * **Chromium:** Part of the Glucose Tolerance Factor (GTF), enhancing insulin action.

Question 273: Which of the following is NOT a reported clinical manifestation of L-asparaginase deficiency in children?

A. Dwarfism and hypogonadism
B. Liver and spleen enlargement
C. Impaired cell-mediated immunity
D. Macrocytic anaemia (Correct Answer)

Explanation: This question tests the understanding of micronutrient deficiencies, specifically **Zinc deficiency**, as "L-asparaginase deficiency" is not a recognized clinical syndrome. In the context of this classic NEET-PG clinical triad, the question refers to the manifestations of Zinc deficiency (often associated with phytate-rich diets or Acrodermatitis enteropathica). ### **Explanation of the Correct Answer** **D. Macrocytic anaemia:** Zinc deficiency is characteristically associated with **microcytic hypochromic anaemia**, not macrocytic anaemia. Macrocytic (megaloblastic) anaemia is typically caused by Vitamin B12 or Folate deficiency. Zinc is a cofactor for enzymes involved in heme synthesis and iron metabolism; thus, its deficiency impairs erythropoiesis, leading to small, pale red blood cells. ### **Analysis of Incorrect Options** * **A. Dwarfism and hypogonadism:** These are hallmark features of Zinc deficiency. Zinc is essential for the function of growth hormone and the development of the gonadal axis. Deficiency leads to stunted growth (dwarfism) and delayed sexual maturation. * **B. Liver and spleen enlargement:** Hepatosplenomegaly is a documented clinical finding in children with chronic nutritional zinc deficiency, often seen alongside growth retardation. * **C. Impaired cell-mediated immunity:** Zinc is vital for T-lymphocyte function and thymic hormone activity (thymulin). Deficiency leads to thymic atrophy and increased susceptibility to infections due to depressed cell-mediated immunity. ### **High-Yield Clinical Pearls for NEET-PG** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder causing severe zinc malabsorption. Clinical triad: **Alopecia, Diarrhea, and Periorificial/Acral dermatitis.** * **Zinc and Wound Healing:** Zinc is a cofactor for **collagenase** (Matrix Metalloproteinases); deficiency leads to poor wound healing. * **Taste Sensation:** Zinc is a component of **gustin**; deficiency causes **hypogeusia** (loss of taste). * **Enzyme Cofactor:** Zinc is a component of over 300 enzymes, including Carbonic anhydrase, Alkaline phosphatase, and Alcohol dehydrogenase.

Question 274: A patient on total parenteral nutrition develops delayed wound healing, loss of taste, deficient immunity, and diarrhea. Most probably, this could be due to deficiency of:

A. Selenium
B. Copper
C. Zinc (Correct Answer)
D. Iron

Explanation: **Explanation:** The clinical presentation of delayed wound healing, **dysgeusia** (loss of taste), impaired immunity, and diarrhea in a patient on Total Parenteral Nutrition (TPN) is a classic manifestation of **Zinc deficiency**. **Why Zinc is the Correct Answer:** Zinc is a vital trace element that acts as a cofactor for over 300 enzymes, including **RNA and DNA polymerases** and **alkaline phosphatase**. It plays a critical role in: * **Cell Division & Protein Synthesis:** Essential for collagen synthesis and epithelialization, explaining why deficiency leads to **delayed wound healing**. * **Immune Function:** Necessary for T-cell proliferation and cytokine production. * **Taste Perception:** Zinc is a component of **gustin**, a protein involved in taste bud development. * **Clinical Sign:** In TPN patients, zinc is often lost through increased gastrointestinal secretions or inadequate supplementation. **Why Other Options are Incorrect:** * **Selenium:** Deficiency typically leads to **Keshan disease** (cardiomyopathy) or muscle weakness, not wound healing issues. * **Copper:** Deficiency manifests as **microcytic anemia** (refractory to iron), neutropenia, and skeletal abnormalities (Menkes-like symptoms). * **Iron:** Primarily leads to **microcytic hypochromic anemia**, fatigue, and pica, but is not the primary cause of acute loss of taste or diarrhea in TPN. **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder of zinc absorption characterized by periorificial and acral dermatitis, alopecia, and diarrhea. * **Zinc & Vitamin A:** Zinc is required for the synthesis of Retinol Binding Protein (RBP); thus, zinc deficiency can lead to secondary Vitamin A deficiency (night blindness). * **TPN Monitoring:** Chromium deficiency in TPN patients can lead to **glucose intolerance** (insulin resistance).

Question 275: Which of the following is deficient in eggs?

A. Vitamin B
B. Vitamin C (Correct Answer)
C. Fat
D. Proteins

Explanation: **Explanation:** The egg is often referred to as a "complete food" because it contains almost all essential nutrients required for life; however, it is notably **deficient in Vitamin C (Ascorbic Acid)** and **complex carbohydrates (fiber)**. **1. Why Vitamin C is the Correct Answer:** Vitamin C is primarily found in citrus fruits and fresh vegetables. In the context of avian development, the developing chick embryo synthesizes its own Vitamin C within the egg or utilizes very negligible amounts that are not significant for human dietary requirements. Therefore, eggs are considered a zero-source of Vitamin C. **2. Analysis of Incorrect Options:** * **Vitamin B:** Eggs are an excellent source of B-complex vitamins, particularly **Vitamin B12 (Cobalamin)**, B2 (Riboflavin), and B5 (Pantothenic Acid). They are also the richest dietary source of **Choline**. * **Fat:** About 33% of an egg's weight is fat, found exclusively in the yolk. It contains phospholipids, cholesterol, and unsaturated fatty acids. * **Proteins:** Eggs contain high-quality protein with a **Biological Value (BV) of 100**, making them the "Gold Standard" against which other food proteins are compared. **High-Yield NEET-PG Pearls:** * **The "Egg Rule":** Eggs lack Vitamin C and Carbohydrates. * **Biological Value:** Egg protein (Albumin) has the highest biological value (100) and Net Protein Utilization (NPU). * **Avidin & Biotin:** Raw egg whites contain **Avidin**, which binds to **Biotin (Vitamin B7)**, preventing its absorption and potentially leading to deficiency (often tested as "Egg white injury"). Cooking denatures avidin, making the biotin bioavailable. * **Iron:** While eggs contain iron, its bioavailability is low due to the presence of phosvitin, which inhibits absorption.

Question 276: Iron absorption is increased by all of the following except?

A. High vitamin C in diet
B. High phosphates in diet (Correct Answer)
C. Ferrous form
D. Acidity

Explanation: ### **Explanation** Iron absorption is a complex process occurring primarily in the **duodenum and upper jejunum**. The absorption efficiency is heavily influenced by the chemical form of iron and the presence of dietary ligands. **Why "High phosphates in diet" is the correct answer:** Phosphates (along with phytates, oxalates, and tannins found in tea/coffee) act as **inhibitors** of iron absorption. They bind to iron in the intestinal lumen to form insoluble, non-absorbable complexes. Therefore, a high phosphate diet **decreases** rather than increases iron absorption. **Analysis of Incorrect Options:** * **High Vitamin C (Ascorbic Acid):** It is a potent enhancer of iron absorption. It acts by reducing ferric iron ($Fe^{3+}$) to the more soluble ferrous form ($Fe^{2+}$) and forming a soluble chelate with iron, preventing its precipitation. * **Ferrous form ($Fe^{2+}$):** Iron is absorbed only in the **ferrous state**. Dietary ferric iron must be reduced to the ferrous state (by gastric HCl or duodenal cytochrome B) before it can be transported into the enterocyte via the DMT-1 transporter. * **Acidity:** Gastric hydrochloric acid (HCl) promotes iron absorption by maintaining iron in its soluble ferrous form and preventing the formation of insoluble hydroxides. --- ### **High-Yield Clinical Pearls for NEET-PG** * **Enhancers of Iron Absorption:** Vitamin C, Citrate, Amino acids (Cysteine), and "Meat factor." * **Inhibitors of Iron Absorption:** Phosphates, Phytates (cereals), Oxalates (spinach), Tannins (tea), and Calcium. * **Hepcidin:** The key negative regulator of iron metabolism; it inhibits iron release by causing the degradation of **Ferroportin**. * **Achlorhydria:** Patients with chronic gastritis or those on long-term Proton Pump Inhibitors (PPIs) are at risk for iron deficiency due to lack of gastric acidity.

Question 277: Positive nitrogen balance is seen in which of the following conditions?

A. Trauma
B. Burns
C. Pregnancy (Correct Answer)
D. Stress

Explanation: **Explanation:** Nitrogen balance is the measure of nitrogen input (primarily dietary protein) minus nitrogen output (urea in urine, feces, and sweat). It serves as an index of protein metabolism in the body. **Why Pregnancy is Correct:** **Positive Nitrogen Balance** occurs when nitrogen intake exceeds excretion ($I > E$). This indicates that the body is actively synthesizing new tissues and retaining protein. **Pregnancy** is a classic physiological state of positive nitrogen balance because amino acids are being utilized for the growth of the fetus, placenta, and maternal uterine/breast tissues. Other examples include growing children and recovery from illness (convalescence). **Why Other Options are Incorrect:** * **Trauma, Burns, and Stress (Options A, B, and D):** These are states of **Negative Nitrogen Balance** ($E > I$). In these conditions, the body is in a hypermetabolic, catabolic state. Increased levels of cortisol and inflammatory cytokines lead to extensive muscle protein breakdown (proteolysis) to provide substrates for gluconeogenesis and acute-phase protein synthesis. This results in excessive nitrogen excretion in the urine. **High-Yield Pearls for NEET-PG:** * **Positive Nitrogen Balance:** Growth, Pregnancy, Convalescence, Anabolic steroid use. * **Negative Nitrogen Balance:** Starvation, Malnutrition (Kwashiorkor/Marasmus), Uncontrolled Diabetes Mellitus, Cancer cachexia, and Severe infection/Sepsis. * **Nitrogen Equilibrium:** Healthy adults maintaining a stable weight where intake equals loss. * **Calculation:** Nitrogen balance is often estimated using the formula: $[(\text{Protein intake in grams}/6.25) - (\text{Urinary Urea Nitrogen} + 4)]$.

Question 278: What glycemic index value is classified as low?

A. 25
B. 45
C. 55 (Correct Answer)
D. 65

Explanation: **Explanation:** The **Glycemic Index (GI)** is a numerical scale (0–100) that ranks carbohydrates based on how quickly they raise blood glucose levels compared to a reference food (usually pure glucose or white bread). **Why 55 is the correct answer:** According to the international classification, the GI categories are defined as follows: * **Low GI:** 55 or less * **Medium GI:** 56 to 69 * **High GI:** 70 or more While options A (25) and B (45) are numerically lower than 55, they both fall within the "Low GI" category. However, in the context of standard medical examinations like NEET-PG, the question asks for the **threshold value** or the upper limit that defines the category. **55** is the specific cutoff point used to classify a food as Low GI. **Analysis of Incorrect Options:** * **A (25) & B (45):** These are examples of low GI values, but they do not represent the standard classification threshold. * **D (65):** This falls into the **Medium GI** category (56–69). Common examples include whole wheat products and raisins. **High-Yield Clinical Pearls for NEET-PG:** * **Glycemic Load (GL):** A more accurate predictor of glycemic response than GI because it accounts for the **portion size** (GL = GI × grams of carbohydrate / 100). * **Low GI Foods:** Legumes, lentils, milk, and most fruits (e.g., apples). These are preferred for patients with Diabetes Mellitus and PCOD. * **High GI Foods:** White rice, white bread, and potatoes. These cause a rapid spike in insulin. * **Factors lowering GI:** Presence of fiber, fat, protein, and acidity (vinegar/lemon) in a meal slows gastric emptying and lowers the overall GI.

Question 279: Which amino acid deficiency can be expected in a case of high cereal intake and poor nutritional balance?

A. Alanine
B. Lysine (Correct Answer)
C. Methionine
D. Cysteine

Explanation: ### Explanation The correct answer is **Lysine**. **1. Why Lysine is Correct:** Cereals (such as wheat, rice, and maize) are the primary dietary staple for a large portion of the population. However, cereal proteins are **incomplete proteins** because they are deficient in certain essential amino acids. Specifically, cereals are notably **low in Lysine** (the first limiting amino acid) and Threonine. In populations with high cereal intake and poor nutritional balance (lack of pulses, animal protein, or dairy), Lysine deficiency is a common clinical expectation. This is why "mutual supplementation"—combining cereals with pulses (which are rich in Lysine but low in Methionine)—is recommended to achieve a balanced amino acid profile. **2. Why Incorrect Options are Wrong:** * **Methionine (C):** This is the limiting amino acid in **pulses/legumes**. Cereals are actually a relatively good source of sulfur-containing amino acids like Methionine. * **Cysteine (D):** Like Methionine, Cysteine is a sulfur-containing amino acid generally found in adequate amounts in cereals. * **Alanine (A):** This is a non-essential amino acid that the body can synthesize endogenously via the transamination of pyruvate; therefore, dietary deficiency is not a clinical concern. **3. NEET-PG High-Yield Clinical Pearls:** * **Limiting Amino Acids:** * **Cereals:** Lysine (most common), Threonine. * **Pulses (Legumes):** Methionine, Cysteine. * **Maize:** Lysine and **Tryptophan** (deficiency leads to Pellagra-like symptoms because Tryptophan is a precursor for Niacin). * **Reference Protein:** Egg protein (Albumin) is considered the "standard" or reference protein with a biological value of 100. * **Biological Value (BV):** Measures how efficiently the body utilizes dietary protein. Animal proteins generally have higher BV than plant proteins.

Question 280: Which of the following has the maximum biological value?

A. Egg (Correct Answer)
B. Milk
C. Soybean
D. Pulses

Explanation: **Explanation:** **Biological Value (BV)** is a measure of the proportion of absorbed protein from a food which becomes incorporated into the proteins of the organism's body. It captures how efficiently the body utilizes dietary protein for growth and maintenance. **1. Why Egg is the Correct Answer:** Egg protein (specifically whole egg) is considered the **"Gold Standard"** in nutrition. It has a Biological Value of **approximately 94–100**, which is the highest among naturally occurring whole foods. This is because eggs contain all essential amino acids in the exact proportions required by the human body, ensuring minimal nitrogen loss through excretion. **2. Analysis of Incorrect Options:** * **Milk (BV ~84-90):** While milk is a high-quality "complete" protein containing casein and whey, its amino acid profile is slightly less efficient for tissue synthesis compared to eggs. * **Soybean (BV ~70-75):** This is the highest quality plant protein but is relatively deficient in sulfur-containing amino acids like **Methionine**. * **Pulses (BV ~50-60):** Most pulses are "incomplete" proteins. They are limited by **Methionine and Cysteine**, though they are rich in Lysine. **3. NEET-PG High-Yield Pearls:** * **Reference Protein:** In many nutritional studies, egg protein is used as the reference (100) to compare other food sources. * **Limiting Amino Acids:** * Pulses/Legumes: Deficient in Methionine; Rich in Lysine. * Cereals: Deficient in Lysine; Rich in Methionine. * **Mutual Supplementation:** Combining cereals and pulses (e.g., Rice and Dal) improves the overall BV of the meal because they compensate for each other's limiting amino acids. * **Net Protein Utilization (NPU):** While BV measures absorbed nitrogen, NPU measures retained nitrogen relative to intake. Egg also ranks highest in NPU (~94).

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

Practice Questions

Functional Foods and Nutraceuticals

Practice Questions

Dietary Guidelines and Recommendations

Practice Questions

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