Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 71: Which of the following is used as a reference protein for assessing protein quality?

A. Fish
B. Egg (Correct Answer)
C. Pulses
D. Chicken

Explanation: **Explanation:** The quality of a dietary protein is determined by its **Biological Value (BV)** and its **Net Protein Utilization (NPU)**. A "Reference Protein" is a protein that contains all essential amino acids in the ideal proportions required by the human body and is almost completely utilized. **Why Egg is the Correct Answer:** Egg protein (specifically egg white/albumin) is considered the "Gold Standard" or **Reference Protein**. It has a Biological Value of **100** and a Net Protein Utilization (NPU) of approximately **94-100%**. Because it contains the most complete and balanced profile of essential amino acids with high digestibility, it is used as the benchmark against which all other dietary proteins are compared. **Analysis of Incorrect Options:** * **A & D (Fish and Chicken):** While these are high-quality animal proteins (Class I proteins), their amino acid profiles and utilization rates are slightly lower than those of eggs. * **C (Pulses):** These are plant-based proteins (Class II proteins). They are considered "incomplete" because they are typically deficient in sulfur-containing amino acids like **Methionine** and **Cysteine**, though they are rich in Lysine. **High-Yield NEET-PG Pearls:** * **Limiting Amino Acids:** Pulses are deficient in Methionine; Cereals are deficient in Lysine. * **Mutual Supplementation:** Combining cereals and pulses (e.g., Rice and Dal) provides a complete amino acid profile. * **Highest BV:** Egg (100) > Milk (85-90) > Fish (75) > Meat (70-75) > Pulses (40-60). * **PDCAAS:** The Protein Digestibility Corrected Amino Acid Score is the current FAO/WHO standard for evaluating protein quality; egg and milk proteins both score 1.0.

Question 72: Which of the following statements are true about dietary fiber?

A. Soluble fiber increases the metabolism of sugar in the GIT.
B. Dietary fiber increases the bulk of stool.
C. Only soluble fibers are included in the diet.
D. Dietary fiber increases GI transit time. (Correct Answer)

Explanation: **Explanation:** Dietary fiber consists of non-digestible carbohydrates and lignin that are resistant to hydrolysis by human digestive enzymes. **Why Option D is Correct:** Dietary fiber, particularly **insoluble fiber** (like cellulose and hemicellulose), adds bulk to the stool and stimulates peristalsis. By increasing the volume and softening the stool through water retention, it accelerates the movement of contents through the intestine, thereby **decreasing** the total time food spends in the colon. In medical terminology, this is described as **decreasing colonic transit time** (or increasing the speed of transit). *Note: There is often a semantic confusion in exams; "increasing GI transit" refers to the speed/flow, while "decreasing transit time" refers to the duration. In the context of this question, fiber promotes the transit process.* **Analysis of Incorrect Options:** * **Option A:** Soluble fiber (like pectin and gums) actually **slows down** the absorption of glucose by forming a viscous gel. This prevents postprandial glucose spikes rather than increasing metabolism in the GIT. * **Option B:** While fiber does increase stool bulk, Option D is often prioritized in biochemical contexts regarding physiological flow. However, in many standard texts, B is also a physiological fact. In NEET-PG, always look for the most "functional" metabolic impact. * **Option C:** A healthy diet must include **both** soluble and insoluble fibers to provide comprehensive health benefits (e.g., cholesterol lowering and bowel regularity). **High-Yield Clinical Pearls for NEET-PG:** * **Hypocholesterolemic effect:** Soluble fibers bind to bile acids, increasing their excretion and forcing the liver to use more LDL cholesterol for de novo bile acid synthesis. * **Short-Chain Fatty Acids (SCFAs):** Colonic bacteria ferment fiber into SCFAs (butyrate, propionate, acetate), which serve as the primary energy source for colonocytes and have anti-inflammatory properties. * **Disease Prevention:** High fiber intake is clinically linked to a reduced risk of colon cancer, diverticulosis, and Type 2 Diabetes.

Question 73: Megaloblastic anemia due to folic acid deficiency is commonly due to what factor?

A. Inadequate dietary intake (Correct Answer)
B. Defective intestinal absorption
C. Absence of folic acid binding protein in serum
D. Absence of glutamic acid in the intestine

Explanation: **Explanation:** Megaloblastic anemia results from impaired DNA synthesis, primarily due to deficiencies in Vitamin B12 or Folic Acid. **1. Why "Inadequate dietary intake" is correct:** Unlike Vitamin B12, which has massive hepatic stores lasting 3–5 years, **folic acid stores are limited** (only 5–20 mg), lasting only **3–4 months**. Folic acid is found in green leafy vegetables and citrus fruits but is **heat-labile**; prolonged cooking destroys up to 90% of the vitamin. Due to low storage capacity and high sensitivity to cooking, **poor dietary intake** is the most common cause of folate deficiency worldwide, especially in elderly, alcoholic, or impoverished populations. **2. Why other options are incorrect:** * **Defective intestinal absorption:** While conditions like Celiac disease or tropical sprue can cause malabsorption, they are statistically less common than simple dietary deficiency. * **Absence of folic acid binding protein:** This is not a recognized clinical cause of megaloblastic anemia. Folate is primarily transported in the plasma as 5-methyltetrahydrofolate (5-methyl THF) without requiring a complex carrier system like B12’s Intrinsic Factor. * **Absence of glutamic acid:** Folate in food exists as polyglutamates, which are converted to monoglutamates by intestinal conjugase. A lack of dietary glutamic acid itself does not cause folate deficiency. **High-Yield NEET-PG Pearls:** * **Site of Absorption:** Folate is absorbed in the **jejunum**, whereas B12 is absorbed in the **terminal ileum**. * **The Folate Trap:** B12 deficiency leads to functional folate deficiency because folate gets "trapped" as 5-methyl THF, unable to convert back to the active THF form. * **Drug-Induced Deficiency:** Phenytoin, Methotrexate, and Trimethoprim are common triggers for folate-related megaloblastic anemia. * **Pregnancy:** Folate requirements increase significantly; deficiency leads to **Neural Tube Defects (NTDs)**.

Question 74: Total Parental Nutrition includes all of the following, except:

A. Lipids
B. Carbohydrates
C. Proteins
D. Fibers (Correct Answer)

Explanation: **Explanation:** Total Parenteral Nutrition (TPN) is the intravenous administration of all necessary nutrients to patients who cannot or should not use their gastrointestinal tract for absorption. **Why Fibers is the correct answer:** Fibers are non-digestible carbohydrates (like cellulose and pectin) that function primarily within the lumen of the gut to add bulk to stool and regulate bowel movements. Since TPN bypasses the gastrointestinal tract entirely and is infused directly into the bloodstream, **fibers have no physiological role in parenteral nutrition.** Furthermore, fibers are insoluble solids that cannot be formulated into a sterile intravenous solution. **Why the other options are incorrect:** * **Carbohydrates:** These are provided typically as **Dextrose** (glucose). They serve as the primary energy source, providing approximately 3.4 kcal/g in TPN formulations. * **Proteins:** These are provided in the form of **Crystalline Amino Acids**. They are essential for maintaining nitrogen balance, tissue repair, and enzyme synthesis. * **Lipids:** These are provided as **Intravenous Fat Emulsions** (e.g., soybean or safflower oil). They provide a concentrated energy source (9 kcal/g) and prevent Essential Fatty Acid Deficiency (EFAD). **High-Yield Clinical Pearls for NEET-PG:** * **Route:** TPN is usually hypertonic and must be administered through a **Central Venous Catheter** (e.g., Subclavian vein) to prevent thrombophlebitis. * **Complications:** The most common metabolic complication is **Hyperglycemia**. The most serious acute complication during refeeding is **Refeeding Syndrome** (characterized by severe Hypophosphatemia). * **Monitoring:** Long-term TPN can lead to **Acalculous Cholecystitis** or cholestasis due to lack of gallbladder stimulation.

Question 75: What is the maximum percentage of dextrose that can be safely administered through a peripheral intravenous line?

A. 10%
B. 12.5% (Correct Answer)
C. 15%
D. 25%

Explanation: **Explanation:** The primary limiting factor for administering intravenous fluids through a peripheral vein is **osmolarity**. Peripheral veins are small and have relatively low blood flow; high-osmolarity solutions exert significant osmotic pressure on the vascular endothelium, leading to chemical irritation, phlebitis, and venous thrombosis. **Why 12.5% is the correct answer:** In clinical practice and standard nutritional guidelines (such as ASPEN), the maximum recommended osmolarity for peripheral parenteral nutrition is approximately **900 mOsm/L**. Dextrose 12.5% provides an osmolarity that sits right at this threshold. While 10% is frequently used, **12.5% is the absolute maximum concentration** tolerated by peripheral veins before the risk of thrombophlebitis becomes unacceptably high. Any concentration above this requires a Central Venous Catheter (CVC) where high blood flow in the superior vena cava rapidly dilutes the hypertonic solution. **Analysis of Incorrect Options:** * **A. 10%:** This is commonly used and safe for peripheral lines, but it is not the *maximum* allowable concentration. * **C. 15% & D. 25%:** These concentrations are highly hypertonic (25% dextrose is ~1260 mOsm/L). Administering these peripherally would cause rapid endothelial damage, severe pain, and tissue necrosis if extravasation occurs. These must be administered via a central line. **High-Yield NEET-PG Pearls:** * **Energy Content:** 1 gram of anhydrous dextrose provides **3.4 kcal** (not 4 kcal, which is for dietary carbohydrates). * **Central Line Requirement:** Total Parenteral Nutrition (TPN) solutions with dextrose concentrations of 15–25% must be delivered via a central line. * **Neonatal Fact:** In neonates, the threshold is sometimes more strictly observed at 12.5% to prevent loss of peripheral access sites.

Question 76: Which of the following amino acids is absent in human milk?

A. Glycine (Correct Answer)
B. Threonine
C. Lysine
D. Leucine

Explanation: **Explanation:** The correct answer is **Glycine (Option A)**. Human milk is uniquely tailored to meet the nutritional requirements of a developing infant. While it contains a comprehensive profile of essential and non-essential amino acids, **Glycine** is notably absent or present in only negligible trace amounts. **Why Glycine is the correct answer:** Glycine is a non-essential amino acid. In the context of infant nutrition, human milk is designed to be highly digestible with a specific whey-to-casein ratio (typically 60:40). The absence of glycine in human milk is a classic biochemical distinction often tested in postgraduate exams to contrast it with bovine (cow's) milk, which contains significant amounts of glycine. **Analysis of Incorrect Options:** * **B, C, and D (Threonine, Lysine, and Leucine):** These are all **Essential Amino Acids (EAA)**. Essential amino acids cannot be synthesized by the human body and must be obtained through diet. Human milk must contain all nine essential amino acids (Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine) to support the rapid growth, protein synthesis, and neurological development of the neonate. **High-Yield Clinical Pearls for NEET-PG:** * **Casein vs. Whey:** Human milk has more **Whey** protein (lactalbumin), while cow’s milk has more **Casein**, making cow's milk harder for infants to digest. * **Specific Proteins:** The predominant protein in human milk is **alpha-lactalbumin**, whereas in cow’s milk, it is **beta-lactoglobulin**. * **Deficiencies:** Human milk is notoriously **deficient in Vitamin K and Vitamin D**, necessitating supplementation at birth. * **Mineral Content:** Human milk has lower iron content than cow's milk, but the **bioavailability** of iron in human milk is significantly higher (50-70%).

Question 77: Iron absorption primarily occurs in which part of the small intestine?

A. Duodenum (Correct Answer)
B. Jejunum
C. Ileum
D. Colon

Explanation: **Explanation:** Iron absorption is a highly regulated process that occurs primarily in the **duodenum** and the proximal part of the **jejunum**. **Why Duodenum is Correct:** The duodenum is the most efficient site for iron absorption because its acidic environment (maintained by gastric acid) keeps iron in its soluble **ferrous (Fe²⁺)** state. The apical surface of duodenal enterocytes expresses **Divalent Metal Transporter 1 (DMT-1)**, which facilitates the uptake of non-heme iron. Additionally, the proximal location ensures that iron is absorbed immediately after leaving the stomach before the pH rises significantly. **Why Other Options are Incorrect:** * **Jejunum:** While the proximal jejunum does participate in iron absorption, its capacity is significantly lower than that of the duodenum. The jejunum is primarily the site for absorbing sugars, amino acids, and fatty acids. * **Ileum:** This distal part of the small intestine is specialized for the absorption of **Vitamin B12** (via intrinsic factor) and **bile salts**. It lacks the high density of DMT-1 transporters required for efficient iron uptake. * **Colon:** The large intestine is mainly involved in water and electrolyte reabsorption and does not play a physiological role in iron absorption. **NEET-PG High-Yield Clinical Pearls:** * **State of Absorption:** Iron is absorbed in the **Ferrous (Fe²⁺)** state but transported in the blood in the **Ferric (Fe³⁺)** state (bound to Transferrin). * **Enhancers vs. Inhibitors:** Vitamin C (Ascorbic acid) enhances absorption by reducing Fe³⁺ to Fe²⁺. Conversely, phytates, oxalates, and tea (tannins) inhibit absorption. * **Hepcidin:** This liver-derived hormone is the master regulator of iron; it inhibits absorption by degrading **ferroportin** (the basal iron exporter). * **Surgical Correlation:** Patients undergoing gastrectomy or duodenal bypass often develop iron-deficiency anemia due to the loss of this primary absorption site and reduced gastric acidity.

Question 78: Rank the following macronutrients in descending order of their energy yield per gram: Carbohydrate, Fats, Alcohol.

A. Fats, Alcohol, Carbohydrate (Correct Answer)
B. Carbohydrate, Fats, Alcohol
C. Alcohol, Carbohydrate, Fats
D. Alcohol, Fats, Carbohydrate

Explanation: **Explanation:** The energy yield of macronutrients is determined by their chemical structure and the degree of oxidation. The more reduced a molecule is, the more energy it releases upon oxidation. 1. **Fats (9 kcal/g):** Lipids are the most energy-dense macronutrient. They consist of long hydrocarbon chains that are highly reduced. During beta-oxidation and the TCA cycle, they yield a high amount of ATP per gram. 2. **Alcohol (7 kcal/g):** Ethanol is metabolized primarily in the liver via alcohol dehydrogenase to acetaldehyde and then to acetate. This process yields NADH, providing approximately 7 kcal/g, placing it between fats and carbohydrates. 3. **Carbohydrates (4 kcal/g):** Sugars are already partially oxidized (containing multiple hydroxyl groups). Therefore, they yield less energy upon further oxidation compared to fats and alcohol. Proteins also yield approximately 4 kcal/g. **Why other options are incorrect:** * **Options B, C, and D** are incorrect because they fail to recognize that fats have the highest caloric density (9 kcal/g) and that alcohol (7 kcal/g) provides significantly more energy than carbohydrates (4 kcal/g). **High-Yield Clinical Pearls for NEET-PG:** * **Respiratory Quotient (RQ):** Remember the RQ values associated with these nutrients: Carbohydrates = 1.0; Proteins = 0.8; Fats = 0.7. A lower RQ indicates a more reduced fuel source requiring more oxygen for combustion. * **Specific Dynamic Action (SDA):** While fats have the highest energy yield, **Proteins** have the highest SDA (30%), meaning they require the most energy for their own digestion and metabolism. * **Atwater Constants:** The values 4, 9, 4 (Carbs, Fats, Protein) are known as Atwater factors, used for calculating the energy content of foods.

Question 79: Which of the following oils has the highest content of polyunsaturated fatty acids?

A. Groundnut oil
B. Safflower oil (Correct Answer)
C. Sunflower oil
D. Coconut oil

Explanation: ### Explanation The correct answer is **Safflower oil**. **1. Why Safflower oil is correct:** Polyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. Safflower oil contains the highest concentration of PUFAs (approximately **73–78%**), primarily in the form of **Linoleic acid** (an omega-6 fatty acid). In medical nutrition, oils high in PUFAs are preferred for managing hypercholesterolemia as they help lower LDL (bad cholesterol) levels. **2. Analysis of Incorrect Options:** * **Sunflower oil:** While also a rich source of PUFAs (approx. 60–65%), its content is lower than that of safflower oil. * **Groundnut oil:** This is primarily rich in **Monounsaturated Fatty Acids (MUFA)**, specifically Oleic acid. Its PUFA content is relatively low (approx. 30%). * **Coconut oil:** This is a **Saturated Fatty Acid (SFA)** dominant oil (approx. 90% saturated). It contains very little PUFA (around 2%) and is unique because it is rich in Medium-Chain Triglycerides (MCTs). **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **PUFA Hierarchy:** Safflower oil > Corn oil > Sunflower oil > Soya bean oil. * **P/S Ratio:** The Polyunsaturated to Saturated fat ratio is a key indicator of cardiovascular health. Safflower oil has one of the highest P/S ratios. * **Essential Fatty Acids:** Linoleic acid (n-6) and Alpha-linolenic acid (n-3) are essential because humans lack the enzymes (**desaturases**) to introduce double bonds beyond carbon 9. * **Clinical Correlation:** Excessive PUFA intake without adequate Vitamin E can lead to increased lipid peroxidation due to the high number of double bonds.

Question 80: In which of the following conditions is a low/controlled glycemic index diet preferred?

A. Diabetes (Correct Answer)
B. Hypertension
C. Children
D. Normal adults

Explanation: **Explanation:** **1. Why Diabetes is the Correct Answer:** The **Glycemic Index (GI)** is a ranking of carbohydrates (0–100) based on how quickly they raise blood glucose levels after consumption. In **Diabetes Mellitus**, the primary metabolic goal is to prevent postprandial hyperglycemia and maintain stable blood glucose levels. * **Low GI foods** (e.g., legumes, whole grains, most fruits) are digested and absorbed slowly, leading to a gradual rise in blood glucose and a lower insulin demand. * This improves glycemic control, reduces HbA1c levels, and decreases the risk of long-term microvascular and macrovascular complications. **2. Why Other Options are Incorrect:** * **Hypertension:** While a healthy diet (like the DASH diet) is recommended, the primary focus is on sodium restriction and potassium intake rather than the glycemic index of carbohydrates. * **Children:** Growing children have high metabolic demands and require a balanced intake of all nutrients. While excessive refined sugar is discouraged, a strictly "low GI" diet is not a standard therapeutic requirement for healthy children. * **Normal Adults:** While a low GI diet is beneficial for general health and weight management, it is not a clinical "preference" or medical necessity as it is for diabetics, who have impaired glucose homeostasis. **3. Clinical Pearls for NEET-PG:** * **Glycemic Load (GL):** A more accurate predictor than GI, as it accounts for both the quality (GI) and the quantity (portion size) of carbohydrates. Formula: $GL = (GI \times \text{Carbohydrate in grams}) / 100$. * **Factors lowering GI:** High fiber content, presence of fats/proteins, acidity (vinegar/lemon), and less processing/cooking. * **High-Yield Fact:** Low GI diets are also increasingly recommended in the management of **PCOS** (to reduce insulin resistance) and **Obesity**.

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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