Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 21: What is the commonest complication of parenteral nutrition?

A. Hyperglycemia
B. Hyperkalemia (Correct Answer)
C. Hyperosmolar dehydration
D. Azotemia

Explanation: **Explanation:** The correct answer is **Hyperkalemia**. Total Parenteral Nutrition (TPN) is a complex intravenous solution containing glucose, amino acids, lipids, and electrolytes. **Hyperkalemia** is frequently cited as the most common metabolic complication of parenteral nutrition. This occurs primarily due to the excessive administration of potassium in the TPN formula relative to the patient's requirements, or as a result of intracellular-to-extracellular shifts in patients with underlying renal impairment or metabolic acidosis. **Analysis of Options:** * **Hyperglycemia (Option A):** While very common (especially in the early stages of TPN or in septic patients), it is often considered a "technical" or "metabolic" risk that is managed by adjusting insulin or infusion rates. In many standardized examinations, electrolyte imbalances like hyperkalemia are statistically noted as more frequent occurrences. * **Hyperosmolar Dehydration (Option C):** This is a severe but less common complication. It occurs if the glucose infusion rate is too high, leading to osmotic diuresis. * **Azotemia (Option D):** This refers to an increase in BUN/Creatinine. It can occur if the amino acid load is too high for the patient's renal capacity, but it is less frequent than electrolyte disturbances. **Clinical Pearls for NEET-PG:** * **Refeeding Syndrome:** A high-yield TPN complication characterized by **Hypophosphatemia**, Hypomagnesemia, and Hypokalemia when feeding is restarted in a malnourished patient. * **Most common infection:** Catheter-related bloodstream infection (CRBSI), often caused by *Staphylococcus aureus* or *Candida*. * **Long-term complication:** TPN-associated liver disease (steatosis and cholestasis). * **Essential Fatty Acid Deficiency (EFAD):** Characterized by a dry, scaly rash (phrynoderma) if lipids are omitted from TPN.

Question 22: All the following are trace elements required by the body except?

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

Explanation: **Explanation:** In human nutrition, minerals are classified based on their daily requirement into **Macro-elements** (>100 mg/day) and **Trace elements** (<100 mg/day). Trace elements are further divided into "Essential" and "Possibly Essential/Non-essential." **Why Boron is the Correct Answer:** Boron is considered a **non-essential** or "ultratrace" element for humans. While it may play a minor role in bone metabolism and vitamin D utilization, it has no established RDA (Recommended Dietary Allowance) and no clearly defined biochemical function or deficiency syndrome in humans. Therefore, in the context of standard medical biochemistry, it is excluded from the list of required trace elements. **Analysis of Incorrect Options:** * **Zinc (A):** An essential trace element. It is a cofactor for over 300 enzymes (e.g., Carbonic anhydrase, Alcohol dehydrogenase) and is crucial for wound healing and DNA synthesis (Zinc fingers). * **Copper (B):** An essential trace element. It is a component of key enzymes like Cytochrome c oxidase, Tyrosinase, and Lysyl oxidase. Its metabolism is central to Wilson’s and Menkes diseases. * **Selenium (C):** An essential trace element. It is incorporated as Selenocysteine into enzymes like **Glutathione peroxidase** (antioxidant defense) and Deiodinase (thyroid hormone conversion). **High-Yield NEET-PG Pearls:** * **Essential Trace Elements:** Fe, Zn, Cu, Se, I, Mn, Mo, Co, Cr, and F. * **Chromium (Cr):** Enhances insulin action (Glucose Tolerance Factor). * **Selenium Deficiency:** Associated with **Keshan disease** (cardiomyopathy). * **Zinc Deficiency:** Leads to **Acrodermatitis enteropathica**, growth retardation, and impaired taste (hypogeusia).

Question 23: Which of the following is considered the reference protein?

A. Fish
B. Egg (Correct Answer)
C. Rice
D. Lemon

Explanation: **Explanation:** The concept of a **Reference Protein** refers to a protein source that contains all essential amino acids in the optimal proportions required by the human body for growth and maintenance. **Why Egg is the Correct Answer:** Egg protein (specifically egg white) is considered the "Gold Standard" or reference protein because it has a **Biological Value (BV) of 100** and a **Net Protein Utilization (NPU) of approximately 94-100%**. It contains the most complete and balanced profile of essential amino acids, making it the benchmark against which the quality of all other dietary proteins is compared. **Analysis of Incorrect Options:** * **A. Fish:** While fish is a high-quality "first-class" protein, its amino acid profile is slightly less balanced than that of an egg. * **C. Rice:** Rice is a plant-based protein and is considered an "incomplete" or "second-class" protein. It is specifically deficient in the essential amino acid **Lysine**. * **D. Lemon:** Lemon is a citrus fruit primarily valued for Vitamin C (Ascorbic acid) and contains negligible amounts of protein. **High-Yield NEET-PG Pearls:** * **Limiting Amino Acids:** Pulses are generally deficient in **Methionine**, while Cereals (like rice/wheat) are deficient in **Lysine**. * **Protein Efficiency Ratio (PER):** This measures weight gain per gram of protein intake. * **PDCAAS (Protein Digestibility Corrected Amino Acid Score):** This is the current international standard for measuring protein quality. Egg and Milk both have a PDCAAS score of **1.0** (the maximum). * **Gelatin:** A unique animal protein that is "incomplete" because it lacks **Tryptophan**.

Question 24: Which food item contains the maximum amount of iron?

A. Pista
B. Cashewnut
C. Meat (Correct Answer)
D. Milk

Explanation: **Explanation:** The correct answer is **Meat**. In the context of nutrition and biochemistry, iron is categorized into two forms: **Heme iron** and **Non-heme iron**. 1. **Why Meat is Correct:** Animal tissues (Meat) contain **Heme iron**, which is the most bioavailable form of iron. It is absorbed directly by the intestinal mucosa via specific heme transporters (HCP1), making its absorption rate (15-35%) significantly higher than plant-based sources. Among the options provided, meat (especially organ meats like liver) provides the highest concentration of readily absorbable iron. 2. **Why other options are incorrect:** * **Pista & Cashewnuts:** These are plant-based sources containing **Non-heme iron**. While they contain iron, it is in the ferric ($Fe^{3+}$) state and is often bound to phytates and oxalates, which inhibit absorption. Their net bioavailability is much lower (2-10%) compared to meat. * **Milk:** Milk is notoriously **poor in iron**. It is often referred to as a "complete food" except for its lack of Iron and Vitamin C. Excessive milk intake in toddlers is a common clinical cause of iron-deficiency anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Absorption Enhancer:** Vitamin C (Ascorbic acid) enhances non-heme iron absorption by reducing $Fe^{3+}$ to $Fe^{2+}$. * **Absorption Inhibitors:** Phytates (cereals), Oxalates (leafy greens), Tannins (tea), and Calcium inhibit iron absorption. * **Storage & Transport:** Iron is stored as **Ferritin** (primary) and Hemosiderin; it is transported in the blood by **Transferrin**. * **Gold Standard:** The most sensitive lab index for iron deficiency anemia is **Serum Ferritin**.

Question 25: Which of the following is cariostatic?

A. Selenium
B. Magnesium
C. Cadmium
D. Molybdenum (Correct Answer)

Explanation: **Explanation:** The term **cariostatic** refers to substances that inhibit or prevent the formation of dental caries (tooth decay). **1. Why Molybdenum is Correct:** Molybdenum is a trace element that has been shown to have a synergistic effect with fluoride. It is incorporated into the enamel surface during the pre-eruptive and post-eruptive stages of tooth development. It enhances the retention of fluoride in the enamel and promotes the formation of a more acid-resistant crystalline structure (fluorapatite), thereby reducing the solubility of enamel to bacterial acids. **2. Analysis of Incorrect Options:** * **Selenium (A) & Cadmium (C):** These are considered **cariogenic** (promote tooth decay). Selenium, if ingested in high amounts during the developmental stage of teeth, can alter the protein matrix of the enamel, making it more susceptible to acid demineralization. Cadmium interferes with the mineralization process. * **Magnesium (B):** While magnesium is essential for bone and tooth health, it is generally considered **caries-inert** or has a negligible effect on the prevention of decay compared to fluoride or molybdenum. **3. Clinical Pearls for NEET-PG:** * **Cariostatic agents:** Fluoride (most potent), Molybdenum, Strontium, Copper, and Iron. * **Cariogenic agents:** Selenium, Cadmium, Manganese, and Magnesium (in some contexts). * **Mechanism of Fluoride:** It inhibits the bacterial enzyme **Enolase** in glycolysis, reducing acid production by oral bacteria (e.g., *S. mutans*). * **Molybdenum Role:** It is also a vital cofactor for enzymes like Xanthine Oxidase, Sulfite Oxidase, and Aldehyde Oxidase.

Question 26: What percentage of proteins does cow's milk contain?

A. 1.1%
B. 3.2% (Correct Answer)
C. 3.5%
D. 4.1%

Explanation: ### Explanation The protein content of milk is a high-yield topic in Biochemistry and Pediatrics for NEET-PG, as it highlights the nutritional differences between human and animal milk. **1. Why 3.2% is Correct:** Cow’s milk contains approximately **3.2% to 3.5% protein** (average 3.2g per 100ml). This is significantly higher than human milk, which contains about **1.1% to 1.2% protein**. The primary protein in cow’s milk is **casein** (about 80%), whereas human milk is rich in **whey** proteins (60% whey, 40% casein), making human milk easier for infants to digest. **2. Analysis of Incorrect Options:** * **Option A (1.1%):** This is the protein content of **human milk**. While lower in quantity, human milk proteins (like lactalbumin and lactoferrin) are of higher biological value and better suited for human infant growth. * **Option C (3.5%):** While some breeds of cows produce 3.5% protein, **3.2%** is the standard value cited in most medical textbooks (like Ghai Pediatrics and Harper’s Biochemistry) for comparative nutrition. * **Option D (4.1%):** This value is too high for protein but roughly corresponds to the **fat content** of cow’s milk (approx. 3.5%–4.5%). **3. Clinical Pearls & High-Yield Facts:** * **Carbohydrates:** Human milk has more lactose (**7%**) compared to cow’s milk (**4.5%**). * **Minerals:** Cow’s milk has 3x more calcium and phosphorus than human milk, which can lead to a high renal solute load in infants. * **Casein:Whey Ratio:** Cow's milk is **80:20** (hard curd), while Human milk is **40:60** (soft, digestible curd). * **Immunoglobulins:** Human milk (especially colostrum) is rich in **IgA**, providing passive immunity, which is absent in processed cow's milk.

Question 27: Technical, infectious, and metabolic complications can occur during total parenteral nutrition (TPN). Which of the following is NOT a complication of TPN?

A. Metabolic bone disease
B. Essential fatty acid deficiency
C. Congestive cardiac failure (Correct Answer)
D. Hypomagnesemia

Explanation: **Explanation:** Total Parenteral Nutrition (TPN) is the intravenous administration of all necessary nutrients, bypassing the gastrointestinal tract. While life-saving, it is associated with various complications categorized as technical, infectious, and metabolic. **Why Congestive Cardiac Failure (CCF) is the correct answer:** CCF is **not** a direct complication of TPN itself. While fluid overload (iatrogenic) can occur during any IV therapy leading to pulmonary edema, it is not a specific metabolic or technical complication inherent to the TPN formulation. In contrast, the other options are well-documented metabolic consequences of long-term or improperly balanced TPN. **Analysis of Incorrect Options:** * **Metabolic Bone Disease (A):** Long-term TPN is associated with osteomalacia and osteoporosis due to negative calcium balance, vitamin D issues, and aluminum toxicity from TPN solutions. * **Essential Fatty Acid Deficiency (EFAD) (B):** This occurs if TPN consists solely of glucose and amino acids without lipid emulsions. Clinical signs include scaly dermatitis and alopecia. * **Hypomagnesemia (D):** This is a common electrolyte abnormality in TPN, often seen as part of **Refeeding Syndrome**, where the shift from catabolism to anabolism causes intracellular uptake of magnesium, phosphate, and potassium. **High-Yield Clinical Pearls for NEET-PG:** * **Most common TPN complication:** Catheter-related bloodstream infection (Sepsis), often due to *Staphylococcus aureus* or *Candida*. * **Refeeding Syndrome:** Characterized by **Hypophosphatemia** (the hallmark), hypokalemia, and hypomagnesemia when starting TPN in malnourished patients. * **Hepatobiliary complications:** TPN-associated cholestasis and cholelithiasis (gallstones) occur due to lack of enteral stimulation and decreased CCK release. * **Hyperglycemia:** The most common metabolic complication during the initiation phase of TPN.

Question 28: What is the energy yield of fats?

A. 4 kcal per gram
B. 6 kcal per gram
C. 8 kcal per gram
D. 9 kcal per gram (Correct Answer)

Explanation: **Explanation:** The energy yield of nutrients is determined by their chemical structure and the degree of oxidation. Fats (lipids) are the most energy-dense macronutrients because they are highly reduced compounds with a high proportion of carbon-hydrogen bonds. **1. Why Option D is Correct:** Fats provide approximately **9 kcal per gram**. During metabolism, fatty acids undergo beta-oxidation, releasing a significant amount of energy. Because fats contain very little oxygen compared to carbohydrates and proteins, they undergo more extensive oxidation, resulting in a higher caloric yield. This makes adipose tissue the most efficient form of long-term energy storage in the human body. **2. Why Other Options are Incorrect:** * **Option A (4 kcal/g):** This is the physiological fuel value for **Carbohydrates** and **Proteins**. While they are essential for immediate energy and structural repair, they are more oxidized than fats and thus yield less than half the energy per gram. * **Option B & C (6 & 8 kcal/g):** These values do not correspond to any major macronutrient. However, **Alcohol (Ethanol)** provides approximately **7 kcal/g**, falling between the values of carbohydrates and fats. **3. NEET-PG High-Yield Pearls:** * **Respiratory Quotient (RQ):** The RQ of fat is **0.7**, which is lower than carbohydrates (1.0) because more oxygen is required to oxidize the lipid molecule. * **Atwater Factors:** The values 4, 9, and 4 kcal/g for carbs, fats, and proteins respectively are known as Atwater factors, used for calculating total dietary energy. * **Storage Efficiency:** 1 gram of glycogen is stored with about 2 grams of water, whereas fat is stored in an anhydrous (water-free) state, further increasing its efficiency as a storage fuel.

Question 29: A patient with type 2 diabetes mellitus is being managed. What type of dietary component is crucial for their management?

A. Proteins
B. Carbohydrates
C. Fats
D. Dietary Fiber (Correct Answer)

Explanation: **Explanation:** **Why Dietary Fiber is Correct:** Dietary fiber, particularly **soluble fiber** (e.g., pectin, gums), plays a pivotal role in the management of Type 2 Diabetes Mellitus (T2DM). It functions by increasing the viscosity of intestinal contents, which **slows the rate of gastric emptying** and delays the absorption of glucose. This results in a blunted postprandial glycemic peak and improved insulin sensitivity. Furthermore, fiber fermentation in the colon produces short-chain fatty acids (SCFAs), which may further enhance metabolic health. **Why Other Options are Incorrect:** * **Carbohydrates:** While essential for energy, high intake—especially of simple sugars—leads to rapid spikes in blood glucose and worsens glycemic control. * **Fats:** High-fat diets, particularly those rich in saturated fats, are associated with increased insulin resistance and cardiovascular risk, which is already elevated in diabetic patients. * **Proteins:** While necessary for muscle maintenance, excessive protein intake does not directly improve glycemic control and may be contraindicated in patients with diabetic nephropathy. **High-Yield Clinical Pearls for NEET-PG:** * **Glycemic Index (GI):** Foods high in fiber typically have a **low GI**, meaning they cause a slower rise in blood glucose levels. * **Lipid Profile:** Soluble fiber also helps lower LDL cholesterol by binding to bile acids in the gut, reducing the risk of macrovascular complications. * **Recommended Intake:** The WHO recommends approximately **25–40g of fiber per day** for optimal metabolic benefits. * **Key Source:** Psyllium husk (Isabgol) is a common clinical recommendation for increasing soluble fiber intake.

Question 30: Iron absorption is increased by:

A. Phytates
B. Tannates
C. Plant food
D. Ascorbic acid (Correct Answer)

Explanation: **Explanation:** Iron absorption is a tightly regulated process occurring primarily in the duodenum and upper jejunum. The correct answer is **Ascorbic acid (Vitamin C)** because it enhances iron absorption through two primary mechanisms: 1. **Reduction:** It reduces dietary ferric iron ($Fe^{3+}$) to the ferrous state ($Fe^{2+}$), which is the only form soluble enough to be absorbed by the divalent metal transporter 1 (DMT1). 2. **Chelation:** It forms a stable, soluble chelate with iron in the acidic environment of the stomach, preventing it from precipitating in the alkaline environment of the small intestine. **Analysis of Incorrect Options:** * **Phytates (Option A):** Found in cereals and legumes, these are potent inhibitors that bind to iron, forming insoluble complexes that cannot be absorbed. * **Tannates (Option B):** Present in tea and coffee, tannates (polyphenols) bind iron in the gut, significantly reducing its bioavailability. * **Plant food (Option C):** Most plant-based iron is **Non-Heme iron** ($Fe^{3+}$), which is inherently less bioavailable (absorption rate 2–5%) compared to Heme iron found in animal products (absorption rate 15–35%). Plant foods also contain fibers and oxalates that further inhibit absorption. **High-Yield Clinical Pearls for NEET-PG:** * **Promoters of Iron Absorption:** Gastric HCl (maintains acidity), Ascorbic acid, and "Meat Factor" (amino acids like cysteine). * **Inhibitors of Iron Absorption:** Phytates, Oxalates, Phosphates (in milk/egg yolk), Tannates, and Calcium. * **Hepcidin:** The key negative regulator of iron absorption; it degrades ferroportin, preventing iron release into the plasma. * **Storage:** Iron is stored as **Ferritin** (soluble) and **Hemosiderin** (insoluble).

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

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Dietary Fiber and Complex Carbohydrates

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Glycemic Index and Glycemic Load

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Micronutrients: Vitamins and Minerals

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Trace Elements and Metabolism

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Malnutrition: Biochemical Consequences

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Dietary Antioxidants

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Functional Foods and Nutraceuticals

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Dietary Guidelines and Recommendations

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