Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 51: Which mineral is present in human milk?

A. Calcium carbonate
B. Calcium and Phosphorus (Correct Answer)
C. Potassium lactate
D. None of the above

Explanation: **Explanation:** Human milk is the gold standard for infant nutrition, providing a balanced profile of macronutrients and essential minerals. **Calcium and Phosphorus** are the primary minerals present in human milk, crucial for the rapid skeletal mineralization and bone development occurring during infancy. * **Why Option B is correct:** Although the absolute concentration of calcium and phosphorus is lower in human milk compared to cow's milk, their **bioavailability** is significantly higher. The Calcium-to-Phosphorus (Ca:P) ratio in human milk is approximately **2:1**, which is considered ideal for maximum absorption and prevents hypocalcemic tetany in neonates. * **Why Option A is incorrect:** Calcium carbonate is a mineral supplement/antacid; calcium in breast milk exists primarily as **calcium caseinate** or is bound to citrate and phosphate, not as carbonate. * **Why Option C is incorrect:** While human milk contains potassium and lactic acid (produced by beneficial bacteria), "Potassium lactate" is a food additive/preservative and not a naturally occurring mineral form in breast milk. **High-Yield NEET-PG Pearls:** 1. **Iron Content:** Human milk is notoriously **low in Iron**, but the iron present has high bioavailability (50% absorption) due to the presence of lactoferrin. 2. **Vitamin Deficiency:** Human milk is deficient in **Vitamin D and Vitamin K**. 3. **The "Whey-to-Casein" Ratio:** In early lactation, the ratio is 80:20, which is easier for the infant to digest compared to cow's milk (20:80). 4. **Major Carbohydrate:** Lactose is the primary sugar, which also aids in calcium absorption.

Question 52: Atkins diet is known for restricting which macronutrient?

A. Protein
B. Carbohydrate (Correct Answer)
C. Fat
D. Minerals

Explanation: **Explanation:** The **Atkins diet** is a classic example of a **low-carbohydrate, high-protein, and high-fat diet**. The fundamental biochemical principle behind this diet is to induce a state of **ketosis**. By severely restricting carbohydrates, the body is forced to switch its primary fuel source from glucose to stored fats. This leads to increased fatty acid oxidation and the production of ketone bodies (acetoacetate, β-hydroxybutyrate, and acetone) in the liver, which serve as an alternative energy source for the brain and muscles. * **Option B (Correct):** Carbohydrates are the primary macronutrient restricted (usually to <20-50g/day in the induction phase). This lowers insulin levels and increases glucagon, stimulating lipolysis. * **Option A & C (Incorrect):** Unlike traditional calorie-restricted diets, the Atkins diet encourages the consumption of proteins and fats to maintain satiety and provide energy. * **Option D (Incorrect):** Minerals are micronutrients, not macronutrients. While some mineral supplementation may be needed due to the diuretic effect of ketosis, they are not the target of restriction. **Clinical Pearls for NEET-PG:** * **Metabolic Shift:** The diet mimics the metabolic state of **starvation** (increased gluconeogenesis and ketogenesis). * **Therapeutic Use:** Ketogenic diets (similar to Atkins) are a high-yield treatment modality for **refractory epilepsy** in children. * **Adverse Effects:** Potential risks include "Keto flu" (electrolyte imbalance), hyperuricemia (due to high protein intake), and increased LDL cholesterol in some individuals. * **Respiratory Quotient (RQ):** On an Atkins diet, the RQ shifts toward **0.7** (indicating pure fat metabolism) from the 1.0 seen in carbohydrate metabolism.

Question 53: Which of the following facilitates the absorption of iron from the intestine?

A. Phytates
B. Coffee
C. Vitamin C (Correct Answer)
D. Vitamin B12

Explanation: **Explanation:** Iron absorption occurs primarily in the duodenum and proximal jejunum. Dietary iron exists in two forms: **Heme iron** (from animal sources) and **Non-heme iron** (from plant sources). **Why Vitamin C is correct:** Non-heme iron is usually in the **Ferric (Fe³⁺)** state, which is insoluble and cannot be absorbed. **Vitamin C (Ascorbic acid)** acts as a potent reducing agent that converts Fe³⁺ into the **Ferrous (Fe²⁺)** state. This form is more soluble and is easily transported across the intestinal apical membrane via the **Divalent Metal Transporter 1 (DMT-1)**. Additionally, Vitamin C forms a soluble chelate with iron, preventing it from precipitating in the alkaline environment of the small intestine. **Why the other options are incorrect:** * **Phytates (Option A):** Found in cereals and legumes, these are "iron inhibitors." They bind to iron to form insoluble complexes, preventing absorption. * **Coffee (Option B):** Contains **polyphenols and tannins** which, similar to phytates, bind iron in the gut and significantly decrease its bioavailability. * **Vitamin B12 (Option D):** While essential for erythropoiesis (red blood cell formation), it has no direct role in the mechanism of intestinal iron absorption. **NEET-PG High-Yield Pearls:** * **Enhancers of Iron Absorption:** Vitamin C, Citrate, and "Meat Factor" (amino acids like Cysteine). * **Inhibitors of Iron Absorption:** Phytates, Oxalates, Tannins (Tea/Coffee), Calcium, and Phosphates. * **Storage & Transport:** Iron is stored as **Ferritin** and transported in the blood by **Transferrin**. * **Hepcidin:** The key negative regulator of iron absorption; it degrades ferroportin, trapping iron inside enterocytes.

Question 54: As compared to cow's milk, human milk has:

A. More proteins
B. Less carbohydrates
C. More iron (Correct Answer)
D. Less vitamins

Explanation: **Explanation:** The composition of human milk is uniquely tailored to the physiological needs of a developing infant. While the absolute concentration of iron in human milk is relatively low (approx. 0.3–0.5 mg/L), it is significantly **more bioavailable** compared to cow’s milk. 1. **Why "More Iron" is the Correct Answer (Contextual Interpretation):** In the context of medical exams, this question refers to the **bioavailability and nutritional efficacy** of iron. About 50% of the iron in human milk is absorbed due to the presence of lactoferrin and high vitamin C levels, whereas only about 10% is absorbed from cow’s milk. Furthermore, cow's milk can cause microscopic intestinal bleeding in infants, leading to iron loss. 2. **Why other options are incorrect:** * **Proteins:** Cow’s milk contains significantly **more protein** (approx. 3.5g/dL) compared to human milk (approx. 1.1g/dL). The protein in cow's milk is primarily casein, which is harder for infants to digest. * **Carbohydrates:** Human milk contains **more carbohydrates** (primarily lactose) than cow’s milk (7g/dL vs 4.5g/dL). Lactose aids in calcium absorption and promotes the growth of *Lactobacillus bifidus*. * **Vitamins:** Human milk generally contains adequate vitamins (except Vitamin D and K), whereas cow's milk is deficient in Vitamin C and E. **High-Yield Clinical Pearls for NEET-PG:** * **Casein to Whey Ratio:** In human milk, it is **40:60**, making it easy to digest. In cow’s milk, it is **80:20**. * **Specific Amino Acids:** Human milk is rich in **Taurine** (essential for brain and retinal development) and **Cysteine**, which cow’s milk lacks. * **Immune Factors:** Human milk is rich in **IgA** and **Lactoferrin**, providing passive immunity that cow's milk cannot replicate. * **Minerals:** Cow's milk has higher Calcium and Phosphorus, but the high solute load can strain neonatal kidneys.

Question 55: Which vitamin is absent in eggs?

A. Vitamin B1
B. Vitamin B6
C. Vitamin C (Correct Answer)
D. Vitamin E

Explanation: **Explanation:** The correct answer is **Vitamin C (Ascorbic Acid)**. Eggs are often described as a "complete food" because they contain almost every essential vitamin and mineral required for life, with one notable exception: Vitamin C. **Why Vitamin C is absent:** Vitamin C is primarily synthesized by plants and is found in citrus fruits and leafy vegetables. While most animals can synthesize Vitamin C endogenously from glucose, the avian embryo does not require an external source of Vitamin C within the egg for its initial development. Consequently, a standard chicken egg contains zero or only negligible traces of Ascorbic Acid. **Analysis of Incorrect Options:** * **Vitamin B1 (Thiamine):** Present in the egg yolk. It is essential for carbohydrate metabolism in the developing embryo. * **Vitamin B6 (Pyridoxine):** Found in eggs; it serves as a vital cofactor for amino acid metabolism (transamination reactions). * **Vitamin E (Tocopherol):** Eggs are a significant source of Vitamin E, which acts as a lipid-soluble antioxidant protecting the high fat content of the yolk from oxidative damage. **High-Yield NEET-PG Pearls:** * **The "Two Absences":** Remember that eggs lack two major nutritional components: **Vitamin C** and **Dietary Fiber**. * **Milk vs. Eggs:** Like eggs, **milk** is also notoriously deficient in Vitamin C and Iron. * **Egg White vs. Yolk:** The egg white (albumin) contains **Avidin**, which binds to **Biotin (B7)** and prevents its absorption, leading to "egg white injury" if consumed raw in large quantities. * **Reference Protein:** Egg protein is considered the "Gold Standard" or Reference Protein (Biological Value = 100) against which other proteins are compared.

Question 56: All of the following conditions will have a hypermetabolic state except:

A. Accident
B. Burns
C. PEM
D. Anorexia nervosa (Correct Answer)

Explanation: **Explanation:** The metabolic state of the body is determined by the **Basal Metabolic Rate (BMR)**. A **hypermetabolic state** is characterized by an increased BMR, usually triggered by systemic inflammation, severe stress, or hormonal imbalances. Conversely, a **hypometabolic state** occurs when the body attempts to conserve energy during periods of prolonged starvation or nutrient deficiency. **Why Anorexia Nervosa is the Correct Answer:** In **Anorexia Nervosa** and **Protein-Energy Malnutrition (PEM)**, the body undergoes an adaptive response to chronic starvation. To preserve vital organ function and survive on limited caloric intake, the body lowers its BMR, leading to a **hypometabolic state**. This is often clinically manifested as bradycardia, hypotension, and hypothermia. *Note: While the question asks for the "except," both PEM and Anorexia Nervosa are technically hypometabolic. However, in competitive exams like NEET-PG, Anorexia Nervosa is the classic prototype for a psychiatric-driven hypometabolic state, whereas PEM is a broader nutritional category.* **Why the other options are incorrect:** * **Accident (Trauma) & Burns:** These are classic examples of the **"Flow Phase"** of the metabolic response to injury. The release of catecholamines, cortisol, and inflammatory cytokines (IL-1, IL-6, TNF-α) causes massive mobilization of energy stores, leading to significant **hypermetabolism**. Burns, in particular, can increase BMR by up to 100%. **High-Yield Clinical Pearls for NEET-PG:** * **Highest BMR Increase:** Major burns (up to 2x normal). * **Hormones increasing BMR:** Thyroxine (T4/T3) is the primary regulator; Epinephrine and Cortisol also increase it. * **Specific Dynamic Action (SDA):** Proteins have the highest SDA (30%), meaning they increase metabolic rate more than fats or carbohydrates during digestion. * **Hypometabolic states:** Hypothyroidism, Starvation, Anorexia Nervosa, and PEM.

Question 57: Which oil contains the highest amount of saturated fatty acids?

A. Soybean oil
B. Groundnut oil
C. Palm oil (Correct Answer)
D. Sunflower oil

Explanation: **Explanation:** The correct answer is **Palm oil**. **1. Why Palm Oil is Correct:** Saturated fatty acids (SFAs) are carboxylic acids with no double bonds between carbon atoms, making them solid or semi-solid at room temperature. Among the given options, **Palm oil** contains approximately **50% saturated fatty acids** (primarily Palmitic acid). While most vegetable oils are rich in unsaturated fats, tropical oils like palm oil and coconut oil are notable exceptions due to their high SFA content. **2. Analysis of Incorrect Options:** * **Soybean oil:** This is a polyunsaturated fatty acid (PUFA) rich oil, containing only about 15% SFAs. It is high in Linoleic acid (Omega-6). * **Groundnut (Peanut) oil:** This is primarily a monounsaturated fatty acid (MUFA) source, containing about 18-20% SFAs. It is rich in Oleic acid. * **Sunflower oil:** This is highly unsaturated, containing roughly 10-12% SFAs and a very high percentage of PUFAs. **3. NEET-PG High-Yield Clinical Pearls:** * **The "Highest" Rule:** While Palm oil is the correct answer among these options, **Coconut oil** actually contains the highest SFA content (~90%) of all dietary oils. * **P/S Ratio:** The Polyunsaturated to Saturated fat ratio is a key health indicator. A higher ratio is generally considered heart-healthy. * **Essential Fatty Acids:** Remember that Linoleic (Omega-6) and Linolenic (Omega-3) acids cannot be synthesized by the body and must be obtained from oils like soybean or sunflower. * **Atherogenic Potential:** High intake of SFAs (like those in palm oil) increases LDL cholesterol, contributing to atherosclerosis, whereas MUFAs and PUFAs are generally cardioprotective.

Question 58: Dietary fibres are composed of which of the following?

A. Polysaccharides
B. Non-starch polysaccharides (Correct Answer)
C. Disaccharides and monosaccharides
D. Monosaccharides

Explanation: **Explanation:** **1. Why "Non-starch polysaccharides" is correct:** 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. Chemically, they are primarily **Non-starch polysaccharides (NSPs)**. While starch consists of $\alpha$-glycosidic bonds (like $\alpha$-1,4 and $\alpha$-1,6) which are easily hydrolyzed by human salivary and pancreatic amylases, dietary fibers contain **$\beta$-glycosidic bonds** (e.g., $\beta$-1,4 linkages in cellulose). Humans lack the specific enzymes (cellulases) required to break these bonds, rendering them indigestible. Common examples include cellulose, hemicellulose, pectins, gums, and mucilages. **2. Why other options are incorrect:** * **Option A (Polysaccharides):** This is too broad. Starch and glycogen are polysaccharides, but they are fully digestible and do not constitute "fiber." * **Option C & D (Disaccharides and Monosaccharides):** These are simple sugars (e.g., glucose, sucrose, lactose). They are rapidly absorbed in the small intestine and provide 4 kcal/g of energy, whereas fiber is complex and non-glycemic. **3. Clinical Pearls for NEET-PG:** * **Components:** Most fibers are NSPs, but **Lignin** is a notable exception—it is a dietary fiber that is a non-carbohydrate polymer (derived from alcohols). * **Classification:** * *Soluble fiber* (Pectin, Gums): Lowers LDL cholesterol and slows glucose absorption. * *Insoluble fiber* (Cellulose, Lignin): Increases stool bulk and relieves constipation. * **Energy Value:** Though traditionally considered zero-calorie, bacterial fermentation of fiber in the colon produces **Short-Chain Fatty Acids (SCFAs)** like butyrate, providing roughly 1.5–2 kcal/g. * **Health Benefit:** High fiber intake is protective against Diverticulosis, Diabetes Mellitus, and Colorectal Cancer.

Question 59: Lysine is deficient in which of the following?

A. Pulses
B. Wheat (Correct Answer)
C. Rice
D. Soyabean

Explanation: **Explanation:** The nutritional quality of a protein is determined by its **limiting amino acid**—the essential amino acid present in the lowest amount relative to human requirements. **Why Wheat is Correct:** Cereals, including **wheat**, maize, and barley, are characteristically deficient in the essential amino acid **Lysine**. Wheat proteins (gliadin and glutenin) are relatively rich in methionine and cysteine (sulfur-containing amino acids) but lack sufficient lysine to support optimal growth if consumed as the sole protein source. This is why a "cereal-pulse combination" (e.g., dal-roti) is nutritionally superior, as they complement each other's deficiencies. **Analysis of Incorrect Options:** * **Pulses (A) and Soyabean (D):** Pulses and legumes are **rich in Lysine** but are deficient in **Methionine** and Cysteine. Soyabean is one of the best plant-based protein sources and contains high levels of lysine. * **Rice (C):** While rice is also a cereal and is relatively low in lysine compared to pulses, it is generally considered to have a better amino acid profile than wheat (it has a higher biological value). However, in the context of standard medical examinations, the classic example of lysine deficiency is always attributed to the cereal group (Wheat/Maize). **High-Yield Clinical Pearls for NEET-PG:** * **Limiting Amino Acids:** * Cereals: Lysine (Threonine is the second limiting amino acid). * Pulses/Legumes: Methionine. * Maize: Lysine and **Tryptophan** (leads to Pellagra as Tryptophan is a precursor for Niacin). * **Reference Protein:** Egg protein (Albumin) is considered the "standard" or reference protein with a biological value of 100. * **Mutual Supplementation:** Combining cereals and pulses provides a complete amino acid profile, a concept known as protein supplementation.

Question 60: Which of the following is an exception for the presence of n-3 PUFA?

A. Mustard oil
B. Corn oil
C. Fish oil
D. Groundnut oil (Correct Answer)

Explanation: ### Explanation The question focuses on the distribution of **Omega-3 (n-3) Polyunsaturated Fatty Acids (PUFAs)** in dietary sources. Omega-3 fatty acids, such as Alpha-linolenic acid (ALA), Eicosapentaenoic acid (EPA), and Docosahexaenoic acid (DHA), are essential fatty acids characterized by a double bond at the third carbon atom from the methyl (omega) end. **Why Groundnut Oil is the Correct Answer:** Groundnut (Peanut) oil is predominantly composed of **Monounsaturated Fatty Acids (MUFA)**, specifically Oleic acid (~50%), and **n-6 PUFA** (Linoleic acid). It contains **negligible to zero amounts of n-3 PUFA**. Therefore, it stands as the exception among the listed options. **Analysis of Incorrect Options:** * **Mustard Oil:** Unlike many other vegetable oils, mustard oil is a significant plant source of **Alpha-linolenic acid (ALA)**, an n-3 PUFA (approx. 6–10%). * **Corn Oil:** While primarily high in n-6 PUFAs, corn oil contains small but measurable amounts of n-3 PUFAs (approx. 1%). In the context of competitive exams, it is generally categorized as containing n-3, unlike groundnut oil. * **Fish Oil:** This is the richest source of long-chain n-3 PUFAs, specifically **EPA and DHA**, which are vital for cardiovascular health and brain function. **High-Yield NEET-PG Pearls:** * **Essential Fatty Acids:** Linoleic acid (n-6) and Alpha-linolenic acid (n-3) are "essential" because humans lack the enzymes (**$\Delta^{12}$ and $\Delta^{15}$ desaturases**) to create double bonds beyond carbon 9. * **P/S Ratio:** The Polyunsaturated to Saturated fat ratio is a key indicator of dietary quality; the ideal ratio is roughly 0.8 to 1.0. * **Clinical Benefit:** n-3 PUFAs reduce serum triglycerides and inhibit VLDL synthesis, providing cardioprotective effects.

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

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Dietary Guidelines and Recommendations

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