Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 231: Which of the following is the least cariogenic?

A. Raw starch (Correct Answer)
B. Cooked starch
C. Sucrose
D. Fructose

Explanation: **Explanation:** The cariogenicity of a carbohydrate (its ability to cause dental caries) depends on how easily oral bacteria, primarily *Streptococcus mutans*, can ferment it into organic acids. These acids lower the plaque pH below 5.5, leading to the demineralization of tooth enamel. **Why Raw Starch is the Correct Answer:** **Raw starch (Option A)** has a complex, crystalline structure that is highly resistant to salivary amylase. Because it does not break down into simple sugars quickly in the oral cavity, it provides minimal substrate for bacterial fermentation. Its low solubility and lack of adherence to tooth surfaces make it the **least cariogenic** of the options provided. **Analysis of Incorrect Options:** * **Cooked Starch (Option B):** Cooking causes gelatinization, breaking down the starch granules and making them easily degradable by salivary amylase into maltose and glucose. Cooked starch is also more "sticky," increasing its retention time on teeth, making it significantly more cariogenic than raw starch. * **Sucrose (Option C):** This is the **most cariogenic** sugar. It is not only fermented into acid but is also used by *S. mutans* to synthesize **extracellular polysaccharides (glucans)**. These glucans allow bacteria to adhere firmly to the enamel (plaque formation). * **Fructose (Option D):** As a monosaccharide, it is rapidly fermented by oral flora. While slightly less cariogenic than sucrose (as it doesn't form glucans as efficiently), it is far more cariogenic than raw starch. **High-Yield Clinical Pearls for NEET-PG:** * **Vipeholm Study:** Established that the frequency of sugar intake and the "stickiness" of food are more critical to caries development than the total amount of sugar consumed. * **Stephan Curve:** Describes the rapid drop in plaque pH after sugar ingestion, followed by a slow recovery. * **Protective Factors:** Fats and proteins are non-cariogenic; certain cheeses may even be anti-cariogenic by promoting remineralization.

Question 232: Which substance is NOT known to have an anti-infective property, either directly or indirectly, in milk?

A. Lactoferrin
B. Lactalbumin (Correct Answer)
C. Lysozyme
D. All of the above

Explanation: **Explanation:** The anti-infective properties of breast milk are primarily mediated by specific proteins and enzymes that inhibit microbial growth. **Why Lactalbumin is the correct answer:** **Lactalbumin** (specifically alpha-lactalbumin) is the principal whey protein in human milk. Its primary biological role is nutritional; it serves as a high-quality source of essential amino acids and acts as a regulatory subunit in the **lactose synthase** complex for lactose production. Unlike the other options, it does not possess direct or indirect antimicrobial or anti-infective properties in its native state. **Why the other options are incorrect:** * **Lactoferrin:** This is a potent bacteriostatic iron-binding protein. It sequesters free iron in the gut, making it unavailable to iron-dependent pathogenic bacteria (like *E. coli*), thereby inhibiting their proliferation. * **Lysozyme:** This enzyme directly attacks the cell walls of Gram-positive bacteria by cleaving the peptidoglycan layer. It remains stable at the low pH of the stomach and works synergistically with lactoferrin. * **Secretory IgA (SIgA):** (Though not listed, it is the most important) It provides mucosal immunity by preventing the attachment of pathogens to the intestinal epithelium. **NEET-PG High-Yield Pearls:** * **Bifidus Factor:** A carbohydrate in milk that promotes the growth of *Lactobacillus bifidus*, which produces lactic acid, lowering intestinal pH and inhibiting pathogens. * **Casein vs. Whey:** Human milk has a higher **Whey:Casein ratio (60:40)** compared to cow’s milk (20:80), making it more digestible for infants. * **HAMLET:** When alpha-lactalbumin binds to oleic acid in the infant's stomach, it forms a complex called HAMLET, which has been shown to induce apoptosis in tumor cells (a niche research fact).

Question 233: Which milk has the highest content of lactose?

A. Buffalo milk
B. Human milk (Correct Answer)
C. Goat milk
D. Cow milk

Explanation: **Explanation:** The correct answer is **Human milk**. Lactose, a disaccharide composed of glucose and galactose, is the primary carbohydrate found in mammalian milk. The concentration of lactose is inversely proportional to the protein content of the milk and is directly related to the brain development requirements of the species. 1. **Why Human Milk is Correct:** Human milk contains the highest concentration of lactose among common mammals, typically ranging from **6.7 to 7.2 g/dL**. This high lactose content is essential for human infants as it provides a critical energy source for rapid brain growth and serves as a precursor for galactolipids (cerebrosides) required for CNS myelination. 2. **Why Other Options are Incorrect:** * **Cow Milk:** Contains approximately **4.4 to 4.8 g/dL** of lactose. It has higher protein and mineral content but lower carbohydrate content compared to human milk. * **Buffalo Milk:** Contains about **4.8 g/dL** of lactose. While it is richer in fats and proteins, its sugar content is significantly lower than human milk. * **Goat Milk:** Contains roughly **4.1 to 4.5 g/dL** of lactose. It is often used as an alternative for those with minor sensitivities but still contains significant lactose and is not the highest source. **High-Yield NEET-PG Pearls:** * **Energy Distribution:** In human milk, approximately 40% of total calories are derived from lactose, whereas 50% come from fats. * **Bifidogenic Effect:** Lactose promotes the growth of *Lactobacillus bifidus* in the infant gut, which lowers intestinal pH and inhibits the growth of pathogens. * **Calcium Absorption:** Lactose enhances the absorption of calcium and magnesium in the neonatal gut. * **Comparison:** Human milk is **High in Lactose/Fat** and **Low in Protein/Minerals** (specifically Calcium/Phosphorus) compared to Cow milk.

Question 234: Which plasma protein is the first to be generated after a severe protein deficiency?

A. Albumin
B. Globulin
C. Fibrinogen (Correct Answer)
D. Thrombin

Explanation: **Explanation:** The correct answer is **Fibrinogen (Option C)**. The synthesis of plasma proteins in the liver is highly sensitive to the availability of amino acids. In states of severe protein deficiency (such as Kwashiorkor or starvation), the liver prioritizes the synthesis of proteins essential for immediate survival and homeostasis. **Fibrinogen** is an acute-phase reactant and a critical component of the coagulation cascade. When protein intake resumes after a period of deficiency, fibrinogen is the first plasma protein to be regenerated and return to normal levels. This is due to its relatively shorter half-life compared to albumin and its physiological priority in maintaining hemostasis. **Analysis of Incorrect Options:** * **Albumin (A):** Although it is the most abundant plasma protein, it has a long half-life (approx. 20 days). Its levels drop significantly in protein-energy malnutrition (PEM) and take the longest time to recover during nutritional rehabilitation. * **Globulin (B):** This is a broad category including immunoglobulins (produced by B-cells, not the liver) and transport globulins. They do not show the same rapid restorative kinetics as fibrinogen. * **Thrombin (D):** Thrombin is an enzyme (activated Factor II) rather than a primary structural plasma protein synthesized in bulk for osmotic or transport purposes. **NEET-PG High-Yield Pearls:** * **Albumin** is the best indicator of **chronic** nutritional status due to its long half-life. * **Pre-albumin (Transthyretin)** is the best indicator of **acute** nutritional changes (half-life of ~2 days). * In **Kwashiorkor**, the decrease in albumin leads to a drop in plasma oncotic pressure, resulting in the characteristic finding of **edema**. * **Transferrin** is another protein used to monitor nutritional status, with a half-life of ~8 days.

Question 235: What are the features of manganese deficiency?

A. Anemia
B. Alopecia
C. Ataxia (Correct Answer)
D. Gonadal atrophy

Explanation: **Explanation:** Manganese (Mn) is an essential trace element that acts as a cofactor for several critical enzymes, including **Pyruvate carboxylase**, **Superoxide dismutase (Mn-SOD)**, and **Arginase**. **Why Ataxia is the Correct Answer:** Manganese is vital for the normal development and function of the central nervous system. It plays a key role in the synthesis of glycosaminoglycans and glycoproteins required for bone and cartilage formation. Deficiency leads to impaired skeletal development and neurological dysfunction. **Ataxia** (loss of muscle coordination) occurs due to the disruption of vestibulocochlear development and impaired neurotransmitter metabolism in the cerebellum and basal ganglia. **Analysis of Incorrect Options:** * **Anemia:** Primarily associated with deficiencies of **Iron** (microcytic), **Vitamin B12/Folate** (megaloblastic), or **Copper** (due to impaired iron transport via ceruloplasmin). * **Alopecia:** Classically seen in **Zinc** deficiency (along with acrodermatitis enteropathica) or Biotin deficiency. * **Gonadal Atrophy:** While manganese deficiency can affect reproductive health in animal models, gonadal atrophy is a hallmark clinical feature of **Zinc** deficiency. **High-Yield Clinical Pearls for NEET-PG:** * **Manganese Toxicity:** Known as **"Manganism,"** it presents with Parkinson-like symptoms (extrapyramidal signs) due to accumulation in the basal ganglia. It is an occupational hazard for miners. * **Mn-Superoxide Dismutase:** Located in the **mitochondria**, it protects cells from oxidative oxidative stress. * **Key Enzyme Link:** Manganese is the specific activator for **Glycosyltransferases**, explaining why deficiency leads to skeletal deformities.

Question 236: All of the following are characteristic features of Kwashiorkor, except –

A. High blood osmolarity (Correct Answer)
B. Hypoalbuminemia
C. Edema
D. Fatty liver

Explanation: **Explanation:** The correct answer is **A. High blood osmolarity**. In Kwashiorkor, the primary physiological state is actually **low blood osmolarity (hypoosmolarity)**. **1. Why "High blood osmolarity" is the correct (incorrect feature) answer:** Kwashiorkor is characterized by a severe deficiency of dietary protein despite adequate calorie intake. This leads to a profound decrease in the synthesis of plasma proteins, primarily albumin. According to Starling’s forces, a decrease in plasma proteins reduces the **plasma oncotic pressure**. This results in a shift of fluid from the intravascular compartment to the interstitial space, leading to hemodilution and a decrease in serum sodium (dilutional hyponatremia), which results in **low blood osmolarity**. **2. Analysis of other options:** * **Hypoalbuminemia (B):** This is the hallmark of Kwashiorkor. Protein deficiency leads to the liver's inability to synthesize albumin. * **Edema (C):** This is the clinical diagnostic feature that distinguishes Kwashiorkor from Marasmus. It is caused by the loss of oncotic pressure due to hypoalbuminemia, leading to "pitting edema" (starting in the feet). * **Fatty liver (D):** Protein deficiency impairs the synthesis of **Apolipoprotein B-100**. Without this protein, VLDLs cannot be formed to export triglycerides out of the liver, leading to hepatic steatosis (fatty change) and hepatomegaly. **Clinical Pearls for NEET-PG:** * **Kwashiorkor:** "Sickness of the older child when the next baby is born." Features: Edema, "Flaky paint" dermatosis, "Flag sign" (banded hair discoloration), and fatty liver. * **Marasmus:** Total calorie malnutrition. Features: Generalized muscle wasting, "Old man/Monkey facies," and **absence of edema**. * **Key differentiator:** Edema is present in Kwashiorkor but absent in Marasmus.

Question 237: Which of the following fats and oils contains the highest proportion of polyunsaturated fatty acids (PUFA)?

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

Explanation: **Explanation:** The correct answer is **Safflower oil**. The classification of dietary fats is based on the predominant type of fatty acid chains they contain: Saturated Fatty Acids (SFA), Monounsaturated Fatty Acids (MUFA), or Polyunsaturated Fatty Acids (PUFA). **1. Why Safflower oil is correct:** Safflower oil contains the highest concentration of PUFA (approximately **73–78%**), primarily in the form of Linoleic acid (an omega-6 essential fatty acid). In medical biochemistry, PUFAs are known to lower serum LDL cholesterol levels, making them a key dietary component for cardiovascular health. **2. Why the other options are incorrect:** * **Coconut oil:** This is a highly **saturated fat** (~90% SFA). It is unique because it is rich in Medium-Chain Triglycerides (MCTs), which are absorbed directly into the portal circulation. * **Groundnut (Peanut) oil:** This is primarily a **MUFA-rich** oil (containing about 40–50% Oleic acid). While it contains PUFA, the proportion is significantly lower than in safflower oil. * **Butter:** This is an animal fat high in **saturated fatty acids** and cholesterol. It also contains short-chain fatty acids like butyric acid. **High-Yield Clinical Pearls for NEET-PG:** * **PUFA Hierarchy:** Safflower oil (75%) > Sunflower oil (65%) > Corn oil (59%) > Soya bean oil (54%). * **MUFA King:** Olive oil is the richest source of MUFA (Oleic acid). * **Essential Fatty Acids:** Linoleic acid (ω-6) and Linolenic acid (ω-3) are PUFAs that cannot be synthesized by the body and must be obtained from the diet. * **P/S Ratio:** The ratio of Polyunsaturated to Saturated fats. A healthy diet typically aims for a P/S ratio of approximately 0.8 to 1.0.

Question 238: Iron absorption is decreased by all except?

A. Calcium
B. Tetracycline
C. Phytate
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 is a potent **enhancer** of iron absorption, whereas the other options are inhibitors. **Why Ascorbic Acid is Correct:** Dietary iron exists in two forms: Heme and Non-heme. Non-heme iron is usually in the ferric state ($Fe^{3+}$), which is insoluble and cannot be absorbed. Ascorbic acid facilitates absorption via two mechanisms: 1. **Reduction:** It reduces $Fe^{3+}$ to the ferrous state ($Fe^{2+}$), which is the form required for transport across the apical membrane via the **Divalent Metal Transporter 1 (DMT-1)**. 2. **Chelation:** It forms a soluble iron-ascorbate complex that remains stable in the alkaline environment of the small intestine. **Why Other Options are Incorrect:** * **Calcium:** It is the only known substance to inhibit the absorption of both heme and non-heme iron by competing for transport pathways. * **Tetracycline:** This antibiotic forms insoluble chelates with iron in the gut, preventing the absorption of both the drug and the mineral. * **Phytates (and Oxalates):** Found in cereals and green leafy vegetables, these bind to iron to form insoluble precipitates, significantly reducing bioavailability. **High-Yield Clinical Pearls for NEET-PG:** * **Hepcidin:** The master regulator of iron homeostasis; it inhibits iron release by degrading **Ferroportin**. * **Achlorhydria:** Gastric acid (HCl) is essential for iron absorption; thus, long-term Proton Pump Inhibitor (PPI) use or gastrectomy leads to iron deficiency. * **Tannins:** Found in tea, these are also potent inhibitors of non-heme iron absorption. * **Storage:** Iron is stored as **Ferritin** (labile) and **Hemosiderin** (stable).

Question 239: Sorghum contains an excess of which amino acid?

A. Lysine
B. Arginine
C. Leucine (Correct Answer)
D. Histidine

Explanation: **Explanation:** **Sorghum (Jowar)** is a staple cereal in many parts of India. The correct answer is **Leucine** because sorghum is unique among cereals for containing high concentrations of this branched-chain amino acid. **Why Leucine is the correct answer:** The high leucine content in sorghum has significant clinical implications. Excess leucine interferes with the metabolic pathway of Tryptophan. Specifically, high levels of leucine inhibit the enzyme **Quinolinate Phosphoribosyl Transferase (QPRT)**, which is essential for converting Tryptophan into Niacin (Vitamin B3). Consequently, populations consuming a diet predominantly based on sorghum are at a high risk of developing **Pellagra**, even if their niacin intake seems borderline adequate. **Analysis of Incorrect Options:** * **A. Lysine:** This is the **limiting amino acid** in almost all cereals, including sorghum. Cereals are characteristically deficient in lysine. * **B. Arginine:** While present in plants, it is not found in "excess" in sorghum and does not carry the same clinical diagnostic weight as leucine. * **D. Histidine:** This is an essential amino acid for children, but it is not a distinguishing feature of sorghum's nutritional profile. **High-Yield Clinical Pearls for NEET-PG:** * **Pellagra 4 D’s:** Dermatitis (Casal’s necklace), Diarrhea, Dementia, and Death. * **Maize vs. Sorghum:** Maize causes Pellagra because it is deficient in Tryptophan and contains "Niacytin" (bound niacin). Sorghum causes Pellagra due to **excess Leucine**. * **Limiting Amino Acids:** * Cereals: Lysine (and Threonine). * Pulses: Methionine (and Cysteine). * **Complementary Proteins:** Mixing cereals (low lysine) with pulses (low methionine) provides a complete amino acid profile.

Question 240: Which of the following are considered dietary fibres?

A. Pectin
B. Lignin
C. Cellulose
D. All of the above (Correct Answer)

Explanation: **Explanation** Dietary fibers are diverse plant-derived carbohydrates and hydrophilic polymers that are resistant to digestion by human endogenous enzymes in the small intestine. They are broadly classified into **Soluble** and **Insoluble** fibers. 1. **Cellulose (Option C):** This is the most abundant insoluble fiber. It is a glucose polymer with $\beta(1\to4)$ glycosidic bonds. Humans lack the enzyme cellulase to break these bonds, making it an indigestible structural component of plant cell walls. 2. **Lignin (Option B):** Unlike most fibers, lignin is a non-carbohydrate polymer (composed of phenylpropane units). It provides structural rigidity to plants and is completely resistant to digestion and bacterial fermentation. 3. **Pectin (Option A):** This is a soluble fiber found in the intercellular layers of fruits (e.g., apples, citrus). It forms a gel-like substance in the GI tract, which slows gastric emptying and glucose absorption. Since all three substances meet the criteria for dietary fiber, **Option D (All of the above)** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Health Benefits:** Dietary fiber increases stool bulk (decreases transit time), prevents constipation, and reduces the risk of colon cancer by diluting potential carcinogens. * **Metabolic Impact:** Soluble fibers (Pectin, Gums) lower LDL cholesterol by binding to bile acids and reducing their enterohepatic circulation. * **Energy Value:** Although indigestible, colonic bacteria ferment some fibers into **Short-Chain Fatty Acids (SCFAs)** like butyrate, which provide energy to colonocytes. * **Glycemic Index:** High-fiber diets lower the glycemic index of meals, aiding in the management of Diabetes Mellitus.

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

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Micronutrients: Vitamins and Minerals

Practice Questions

Trace Elements and Metabolism

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Malnutrition: Biochemical Consequences

Practice Questions

Dietary Antioxidants

Practice Questions

Functional Foods and Nutraceuticals

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Dietary Guidelines and Recommendations

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