Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 81: Copper deficiency manifests as which of the following?

A. Anaemia (Correct Answer)
B. Cardiomyopathy
C. Hepatomegaly
D. Hypothyroidism

Explanation: **Explanation:** **Why Anaemia is the correct answer:** Copper is an essential trace element required for the function of **Ferroxidases** (specifically **Ceruloplasmin** and **Hephaestin**). These enzymes oxidize ferrous iron ($Fe^{2+}$) to ferric iron ($Fe^{3+}$), which is the only form that can bind to Transferrin for transport to the bone marrow. In copper deficiency, iron cannot be mobilized from storage sites (liver and macrophages), leading to a functional iron deficiency. This typically manifests as a **microcytic hypochromic anaemia** that is unresponsive to iron therapy but responds to copper supplementation. Additionally, copper is a cofactor for cytochrome c oxidase, essential for heme synthesis. **Why the other options are incorrect:** * **Cardiomyopathy:** While severe copper deficiency can affect cardiac muscle in animal models (e.g., Keshan disease is linked to Selenium, not Copper), it is not a classic clinical manifestation in humans. Cardiomyopathy is more characteristically associated with **Selenium deficiency**. * **Hepatomegaly:** Copper *excess* (as seen in **Wilson’s Disease**) leads to hepatomegaly and cirrhosis due to toxic accumulation. Deficiency does not typically cause liver enlargement. * **Hypothyroidism:** This is primarily associated with **Iodine deficiency** or Selenium deficiency (as deiodinase enzymes are selenoproteins). **High-Yield Clinical Pearls for NEET-PG:** * **Menkes Kinky Hair Syndrome:** An X-linked recessive disorder caused by a defect in the **ATP7A** gene, leading to impaired copper absorption and systemic deficiency. Clinical features include "steely" or "kinky" hair, growth retardation, and neurological degeneration. * **Pancytopenia:** Severe copper deficiency can also cause neutropenia and mimic myelodysplastic syndrome (sideroblastic changes in bone marrow). * **Cofactor Roles:** Remember copper is a cofactor for **Lysyl oxidase** (collagen cross-linking), **Tyrosinase** (melanin synthesis), and **Superoxide Dismutase** (antioxidant).

Question 82: What is the minimum amount of protein required daily to achieve a positive nitrogen balance?

A. 20-30 gm/day
B. 35-40 gm/day
C. 50 gm/day
D. 60 gm/day (Correct Answer)

Explanation: **Explanation** The correct answer is **60 gm/day**. **1. Underlying Medical Concept** Nitrogen balance is the measure of nitrogen input (protein intake) minus nitrogen output (urea in urine, feces, and sweat). To achieve a **positive nitrogen balance**—where the body retains more nitrogen than it excretes—the intake must exceed the **obligatory nitrogen loss**. In a healthy adult weighing approximately 70 kg, the Recommended Dietary Allowance (RDA) for protein is **0.8 to 1.0 g/kg body weight/day**. This translates to roughly **56–70 gm/day**. At this level, the body can adequately perform tissue repair, enzyme synthesis, and growth. An intake of 60 gm/day ensures that the anabolic processes exceed catabolic breakdown, shifting the body into a positive nitrogen state. **2. Analysis of Incorrect Options** * **A (20-30 gm/day) & B (35-40 gm/day):** These amounts are below the minimum physiological requirement. At these levels, the body enters a **negative nitrogen balance**, leading to muscle wasting and protein-energy malnutrition (PEM) because obligatory losses exceed intake. * **C (50 gm/day):** While closer to the requirement, 50 gm is often considered the "bare minimum" to maintain equilibrium (zero balance) in smaller individuals, but it is insufficient to reliably ensure a *positive* balance in a standard adult population. **3. High-Yield Clinical Pearls for NEET-PG** * **Positive Nitrogen Balance:** Seen during growth, pregnancy, and recovery from illness/surgery. * **Negative Nitrogen Balance:** Seen in starvation, severe burns, sepsis, and uncontrolled diabetes. * **Biological Value (BV):** Egg protein has a BV of 100 and is the "Reference Protein." * **Kwashiorkor vs. Marasmus:** Kwashiorkor is a deficiency of protein despite adequate calories (presents with edema); Marasmus is a deficiency of both protein and total calories (presents with "skin and bones" appearance).

Question 83: Iron absorption is increased in which of the following conditions?

A. Iron deficiency anemia, Malignancy
B. Pregnancy, Malignancy
C. Iron deficiency anemia, Pregnancy (Correct Answer)
D. Iron deficiency anemia, Pregnancy, Malignancy

Explanation: **Explanation:** Iron absorption is a tightly regulated process occurring primarily in the **duodenum and proximal jejunum**. The body’s iron status and erythropoietic demand are the primary regulators of this process. **Why Option C is Correct:** 1. **Iron Deficiency Anemia (IDA):** When body iron stores are low, the liver decreases the production of **Hepcidin** (the master regulator of iron). Low hepcidin levels allow for increased expression of **Ferroportin** on the basolateral membrane of enterocytes, facilitating greater iron transport into the blood. 2. **Pregnancy:** During pregnancy, there is a massive physiological demand for iron to support fetal growth, placental development, and increased maternal red cell mass. This state of "ineffective erythropoiesis" and high demand signals the body to suppress hepcidin, thereby maximizing intestinal iron absorption. **Analysis of Incorrect Options:** * **Malignancy (Options A, B, and D):** Chronic diseases, including malignancies and chronic infections, induce a state of inflammation. Inflammatory cytokines (specifically **IL-6**) stimulate the liver to **increase Hepcidin** production. High hepcidin levels degrade ferroportin, trapping iron inside macrophages and enterocytes, leading to **decreased** serum iron absorption (Anemia of Chronic Disease). **NEET-PG High-Yield Pearls:** * **Hepcidin:** It is an acute-phase reactant. High Hepcidin = Low Iron Absorption; Low Hepcidin = High Iron Absorption. * **Vitamin C (Ascorbic Acid):** Enhances iron absorption by reducing ferric ($Fe^{3+}$) iron to the more soluble ferrous ($Fe^{2+}$) form. * **Inhibitors of Absorption:** Phytates (cereals), Oxalates (spinach), Tannins (tea), and Calcium inhibit non-heme iron absorption. * **DMT-1 (Divalent Metal Transporter 1):** The primary transporter for apical entry of non-heme iron into the enterocyte.

Question 84: Colonic bacteria, upon digestion of dietary fibers, produce which of the following?

A. Free radicals
B. Glycerol
C. Butyrate (Correct Answer)
D. Sucrose

Explanation: **Explanation:** The correct answer is **Butyrate**. Dietary fibers (non-starch polysaccharides like cellulose and pectin) are resistant to human digestive enzymes in the small intestine. Upon reaching the large intestine, they undergo anaerobic fermentation by the gut microbiota (colonic bacteria). This process primarily produces **Short-Chain Fatty Acids (SCFAs)**, specifically **Acetate, Propionate, and Butyrate.** * **Butyrate (Butyric acid):** This is the most significant SCFA for colonic health. It serves as the **primary fuel source for colonocytes** (epithelial cells of the colon) and plays a crucial role in maintaining mucosal integrity, inducing apoptosis in colon cancer cells, and exerting anti-inflammatory effects. **Why other options are incorrect:** * **Free radicals:** These are unstable molecules produced during oxidative stress or metabolic reactions; bacterial fermentation of fiber is generally a protective process that reduces oxidative damage. * **Glycerol:** This is a backbone of triglycerides, released during lipolysis (fat digestion), not fiber fermentation. * **Sucrose:** This is a disaccharide (table sugar) that is normally digested by sucrase in the small intestine into glucose and fructose. **NEET-PG High-Yield Pearls:** 1. **SCFA Ratio:** The typical molar ratio of SCFAs produced in the colon is Acetate (60%) > Propionate (25%) > Butyrate (15%). 2. **Metabolic Fates:** While Butyrate is used locally by colonocytes, **Propionate** travels to the liver for gluconeogenesis, and **Acetate** enters the peripheral circulation for cholesterol synthesis or oxidation in muscle. 3. **Prebiotics:** Dietary fibers are considered "prebiotics" because they selectively stimulate the growth of beneficial bacteria (like *Bifidobacterium*). 4. **Health Benefit:** High fiber intake is clinically linked to a decreased risk of colorectal cancer and diverticulosis due to these fermentation byproducts.

Question 85: Which of the following terms describes substances that supply carbohydrate polymers and also contain non-carbohydrate polymers that aid in digestion?

A. Monosaccharide
B. Disaccharide
C. Polysaccharide
D. Dietary fibers (Correct Answer)

Explanation: ### Explanation **1. Why Dietary Fibers is the Correct Answer:** Dietary fibers are defined as the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine. They primarily consist of **carbohydrate polymers** (such as cellulose, hemicellulose, and pectins) but crucially also contain **non-carbohydrate polymers**, most notably **lignin**. These substances aid in digestion by increasing fecal bulk, promoting peristalsis, and slowing the absorption of glucose and cholesterol. **2. Why the Other Options are Incorrect:** * **A. Monosaccharides:** These are the simplest form of carbohydrates (e.g., glucose, fructose). They are single units, not polymers, and do not contain non-carbohydrate components. * **B. Disaccharides:** These consist of two monosaccharide units (e.g., sucrose, lactose). Like monosaccharides, they are simple sugars and lack the complex structural non-carbohydrate polymers found in fiber. * **C. Polysaccharides:** While this is a broad category that includes starch and glycogen (digestible) as well as cellulose (indigestible), the term "polysaccharide" refers strictly to carbohydrate chains. It does not inherently account for the non-carbohydrate polymers (like lignin) specified in the question. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Lignin** is the only significant non-carbohydrate component of dietary fiber; it is a complex polymer of aromatic alcohols. * **Soluble vs. Insoluble:** Soluble fibers (pectins, gums) help lower LDL cholesterol; insoluble fibers (cellulose, lignin) prevent constipation. * **Short-Chain Fatty Acids (SCFAs):** Colonic bacteria ferment soluble fiber into SCFAs (acetate, propionate, butyrate), which provide energy to colonocytes and may prevent colon cancer. * **Recommended Intake:** The WHO recommends approximately **25–40g** of dietary fiber per day for adults.

Question 86: Which of the following is most commonly used to assess protein utilization?

A. Net protein utilization (NPU) (Correct Answer)
B. Amino acid score
C. Biological value
D. Protein efficiency ratio

Explanation: **Explanation:** The assessment of dietary protein quality is a high-yield topic in biochemistry and nutrition. The correct answer is **Net Protein Utilization (NPU)** because it is the most comprehensive practical index for assessing how well the body utilizes a specific protein. **1. Why Net Protein Utilization (NPU) is correct:** NPU measures the proportion of dietary protein that is actually retained by the body. It is calculated as: $$\text{NPU} = \text{Biological Value (BV)} \times \text{Digestibility Coefficient}$$ Unlike Biological Value, which only considers the nitrogen absorbed, NPU accounts for **digestibility**. Since it reflects both the quality (amino acid profile) and the quantity of protein actually utilized after digestion, it is the most common parameter used in clinical and nutritional assessments. **2. Why the other options are incorrect:** * **Biological Value (BV):** Measures the percentage of *absorbed* nitrogen retained by the body. It ignores the nitrogen lost in feces (undigested protein), making it less accurate than NPU for overall utilization. * **Amino Acid Score (Chemical Score):** A theoretical measure that compares the essential amino acid content of a test protein to a reference protein (usually egg). It does not account for human digestion or metabolism. * **Protein Efficiency Ratio (PER):** Measures weight gain in growing animals (usually rats) per gram of protein consumed. It is less commonly used for human clinical assessment as weight gain is not solely dependent on protein intake. **Clinical Pearls for NEET-PG:** * **Reference Protein:** Egg protein is considered the "Gold Standard" with an NPU and BV of approximately 100. * **Limiting Amino Acids:** Pulses are deficient in Methionine; Cereals are deficient in Lysine. * **PDCAAS:** The Protein Digestibility Corrected Amino Acid Score is currently the internationally accepted standard for evaluating protein quality in human nutrition.

Question 87: What is the energy generated from alcohol?

A. 4 kcal/g
B. 0 kcal/g
C. 7 kcal/g (Correct Answer)
D. 9 kcal/g

Explanation: ### Explanation The energy content of food substances is determined by their caloric density, which represents the amount of energy released during complete oxidation. **1. Why 7 kcal/g is Correct:** Alcohol (Ethanol) is metabolized primarily in the liver. It undergoes oxidation by **Alcohol Dehydrogenase (ADH)** to acetaldehyde and then by **Aldehyde Dehydrogenase (ALDH)** to acetate. These reactions generate NADH, which enters the electron transport chain to produce ATP. The physiological fuel value of pure ethanol is approximately **7.1 kcal/g**, making it more energy-dense than carbohydrates but less than fats. **2. Analysis of Incorrect Options:** * **A. 4 kcal/g:** This is the physiological fuel value for **Carbohydrates and Proteins**. These are the primary sources of energy in a balanced diet. * **B. 0 kcal/g:** This applies to non-caloric substances like water, vitamins, minerals, and dietary fiber (cellulose), which do not provide metabolic energy. * **D. 9 kcal/g:** This is the caloric value of **Lipids (Fats)**. Fats are the most energy-dense macronutrients because they are highly reduced molecules. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Empty Calories:** Alcohol is often termed "empty calories" because it provides energy without essential nutrients (minerals/vitamins). * **MEOS Pathway:** In chronic alcoholics, the **Microsomal Ethanol Oxidizing System (CYP2E1)** is induced. This pathway is less energy-efficient as it utilizes NADPH, potentially leading to a lower net ATP yield compared to the ADH pathway. * **Metabolic Impact:** High alcohol intake increases the **NADH/NAD+ ratio**, which inhibits gluconeogenesis (leading to fasting hypoglycemia) and promotes fatty acid synthesis (leading to fatty liver/steatosis). * **Specific Dynamic Action (SDA):** Alcohol has a high thermic effect, meaning a significant portion of its energy is dissipated as heat.

Question 88: Menkes disease is due to deficiency of:

A. Selenium
B. Copper (Correct Answer)
C. Chromium
D. Manganese

Explanation: **Explanation:** **Menkes Disease (Kinky Hair Syndrome)** is an X-linked recessive disorder caused by a mutation in the **ATP7A gene**. This gene encodes a P-type ATPase protein responsible for the absorption of dietary copper from the intestine and its transport across the blood-brain barrier. In Menkes disease, copper is trapped within intestinal mucosal cells and cannot reach the systemic circulation, leading to severe **systemic copper deficiency**. **Why Copper is the Correct Answer:** Copper is a vital cofactor for several enzymes. Its deficiency leads to the clinical manifestations of Menkes disease: * **Lysyl Oxidase:** Impaired cross-linking of collagen and elastin (leads to arterial tortuosity and skeletal issues). * **Tyrosinase:** Failure of melanin synthesis (leads to hypopigmentation). * **Cytochrome c Oxidase:** Impaired oxidative phosphorylation (leads to neurodegeneration). * **Dopamine β-hydroxylase:** Impaired catecholamine synthesis. **Why Other Options are Incorrect:** * **Selenium:** Deficiency is associated with **Keshan disease** (cardiomyopathy) and Kashin-Beck disease (osteoarthritis). * **Chromium:** Deficiency leads to impaired glucose tolerance (insulin resistance) as chromium is a component of the Glucose Tolerance Factor (GTF). * **Manganese:** Deficiency is rare but can lead to impaired growth, skeletal abnormalities, and defects in carbohydrate/lipid metabolism. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Sign:** "Steely" or "Kinky" hair (pili torti) due to defective keratin disulfide bond formation. * **Diagnosis:** Low serum copper and low serum ceruloplasmin levels. * **Contrast with Wilson Disease:** Wilson disease involves the **ATP7B gene**, leading to copper **overload** (toxic accumulation) rather than deficiency. * **Inheritance:** X-linked Recessive (primarily affects males).

Question 89: In Protein Energy Malnutrition, which of the following immunoglobulins is most reduced?

A. IgG
B. IgM
C. IgA (Correct Answer)
D. IgE

Explanation: **Explanation:** In Protein-Energy Malnutrition (PEM), such as Kwashiorkor and Marasmus, the immune system is significantly compromised, a state often referred to as "nutritionally acquired immunodeficiency." **Why IgA is the correct answer:** The most characteristic immunological defect in PEM is the reduction of **Secretory IgA (sIgA)**. This occurs due to the atrophy of mucosal surfaces and lymphoid tissues (like Peyer's patches). Since IgA is the primary mediator of mucosal immunity, its deficiency leads to a breakdown of the protective barrier in the respiratory and gastrointestinal tracts. This explains why children with PEM are highly susceptible to recurrent infections like pneumonia and infectious diarrhea. **Analysis of Incorrect Options:** * **IgG and IgM:** Interestingly, serum levels of IgG, IgM, and IgD are usually **normal or even elevated** in PEM. This is because the body maintains its ability to produce these systemic antibodies in response to the frequent underlying infections common in malnourished states. * **IgE:** Serum IgE levels are often **increased** in PEM, particularly in developing regions, primarily due to the high prevalence of co-existing parasitic (helminthic) infestations. **High-Yield Clinical Pearls for NEET-PG:** * **Cell-Mediated Immunity (CMI):** This is the most severely affected component of the immune system in PEM. There is marked **thymic atrophy**, reduced T-cell counts, and a negative Mantoux test (anergy) even in the presence of TB. * **Complement System:** Levels of most complement components (except C4) are significantly reduced. * **Phagocytosis:** While the number of neutrophils is usually normal, their **bactericidal activity** (oxidative burst) is impaired.

Question 90: Intake of a high protein diet causes which of the following?

A. Increased gluconeogenesis (Correct Answer)
B. Increased beta oxidation
C. Decreased glycogenolysis
D. Metabolic alkalosis

Explanation: **Explanation:** **Why Option A is Correct:** A high-protein diet leads to an abundance of amino acids in the portal circulation. Unlike glucose or fats, the body has no dedicated storage form for excess protein. Therefore, surplus amino acids undergo **deamination**. The resulting carbon skeletons are primarily used as substrates for **gluconeogenesis** in the liver. Glucogenic amino acids (like alanine and glutamine) are converted into pyruvate or TCA cycle intermediates, which are then utilized to synthesize glucose. This process is further stimulated by the fact that high protein intake triggers the release of **glucagon**, a potent activator of gluconeogenic enzymes (e.g., PEPCK). **Why Other Options are Incorrect:** * **B. Increased Beta-oxidation:** Beta-oxidation is the breakdown of fatty acids, typically triggered by starvation or a high-fat (ketogenic) diet, not a high-protein diet. * **C. Decreased Glycogenolysis:** While gluconeogenesis increases, glycogenolysis is not necessarily decreased; in a high-protein, low-carb context, glycogenolysis may actually be maintained or increased to stabilize blood glucose levels. * **D. Metabolic Alkalosis:** High protein intake, especially from animal sources, increases the "acid ash" load due to the metabolism of sulfur-containing amino acids (methionine/cysteine), which can lead to a mild **metabolic acidosis**, not alkalosis. **High-Yield NEET-PG Pearls:** * **Specific Dynamic Action (SDA):** Protein has the highest SDA (~30%), meaning it requires more energy for digestion and processing than fats or carbs. * **Nitrogen Balance:** In healthy adults, nitrogen intake equals nitrogen excretion. A high-protein diet increases urea synthesis via the **Urea Cycle** to detoxify the ammonia produced during deamination. * **Glucagon-Insulin Ratio:** High protein meals stimulate both insulin (to promote protein synthesis) and glucagon (to prevent hypoglycemia from insulin), but the glucagon effect predominates in driving gluconeogenesis.

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

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