Nutrition and Metabolism — MCQs

Nutrition and Metabolism Indian Medical PG Practice Questions and MCQs

Question 101: What organ has the maximum storage of Magnesium (Mg)?

A. Liver
B. Bones (Correct Answer)
C. Kidney
D. Intestine

Explanation: **Explanation:** Magnesium (Mg²⁺) is the second most abundant intracellular cation in the body (after Potassium). The total body magnesium content is approximately **25 grams**, and its distribution is highly compartmentalized. **1. Why Bones (Correct Answer) is right:** The **bones** serve as the primary reservoir for magnesium, containing approximately **60% to 65%** of the total body magnesium. About one-third of this skeletal magnesium is located on the surface of the bone (hydroxyapatite crystals) and acts as a dynamic pool that can be exchanged with the serum to maintain magnesium homeostasis during periods of deficiency. **2. Why the other options are wrong:** * **Liver:** While the liver is a major storage site for glycogen, iron (ferritin), and Vitamin B12, it contains only a small fraction of the body's magnesium (part of the ~35% found in soft tissues). * **Kidney:** The kidney is the primary organ for **excretion and regulation** of magnesium levels (via the Loop of Henle), but it does not store significant quantities. * **Intestine:** The intestine (specifically the ileum and colon) is the site of magnesium **absorption**, not storage. **3. NEET-PG High-Yield Clinical Pearls:** * **Distribution:** 60% in Bone > 39% Intracellular (mainly Muscle/Soft tissue) > 1% Extracellular (Serum). * **Serum Levels:** Normal range is **1.7–2.4 mg/dL**. Note that serum levels may appear normal even if total body stores (bone) are depleted. * **Enzymatic Role:** Magnesium is a mandatory cofactor for all enzymes utilizing or synthesizing **ATP** (e.g., Kinases). * **Hypomagnesemia Link:** Low magnesium can cause **refractory hypokalemia** and **hypocalcemia** (due to decreased PTH secretion and resistance). Always correct Mg²⁺ before K⁺.

Question 102: Which of the following plant parts does not contain keratin?

A. Potato (Correct Answer)
B. Tomato
C. Carrot
D. Spinach

Explanation: **Explanation:** The question contains a common terminology trap often encountered in biochemistry. In the context of plant nutrition, the term "keratin" is frequently used as a distractor for **Carotenoids** (specifically **Beta-carotene**). **1. Why Potato is the Correct Answer:** Potatoes are primarily composed of **starch** (amylopectin and amylose). While they contain small amounts of Vitamin C and B6, they are notably deficient in carotenoids (the precursors to Vitamin A). In biological terms, **Keratin** is a structural protein found in animals (hair, nails, skin) and is **never** found in any plant. However, in the context of this specific question type, it refers to the absence of yellow-orange pigments (carotenoids). **2. Analysis of Incorrect Options:** * **Carrot:** The richest source of $\beta$-carotene (the name "carotene" is derived from carrot). It is a potent provitamin A source. * **Spinach:** Although green due to chlorophyll, spinach is very high in $\beta$-carotene and lutein. The green pigment simply masks the orange carotenoids. * **Tomato:** Contains high levels of **Lycopene** and $\beta$-carotene, both of which belong to the carotenoid family. **3. NEET-PG High-Yield Pearls:** * **Vitamin A Precursor:** $\beta$-carotene is cleaved by the enzyme **$\beta$-carotene 15,15'-dioxygenase** in the intestinal mucosa to form two molecules of Retinal. * **Golden Rice:** A genetically modified variety of rice created to biosynthesize $\beta$-carotene to prevent Vitamin A deficiency. * **Clinical Correlation:** Excessive intake of the plants listed in options B, C, and D can lead to **Carotenemia** (yellowish discoloration of the skin), which is distinguished from jaundice by the **absence of scleral icterus**.

Question 103: Which of the following statements is FALSE regarding Keshan's disease?

A. It is caused by selenium excess. (Correct Answer)
B. It is an endemic cardiomyopathy found in China.
C. It is associated with an increased intake of maize.
D. It is most commonly observed in children and women of childbearing age.

Explanation: **Explanation:** **1. Why Option A is the Correct Answer (The False Statement):** Keshan’s disease is caused by a **deficiency** of Selenium, not an excess. Selenium is a vital trace element that serves as a cofactor for the enzyme **Glutathione Peroxidase**, which protects cells from oxidative damage. In the absence of selenium, oxidative stress leads to myocardial necrosis. Selenium excess, on the other hand, leads to **Selenosis**, characterized by garlic breath, hair loss, and nail changes. **2. Analysis of Other Options:** * **Option B:** It is indeed an **endemic cardiomyopathy** first identified in the Keshan province of **China**, where the soil is severely depleted of selenium. * **Option C:** It is associated with an increased intake of **maize** (corn) grown in selenium-poor soil. Maize-based diets often lack diverse micronutrients, exacerbating the deficiency in these specific geographic regions. * **Option D:** The disease predominantly affects vulnerable populations, specifically **children and women of childbearing age**, likely due to higher physiological demands for trace elements. **3. High-Yield Clinical Pearls for NEET-PG:** * **Enzyme Link:** Selenium is essential for **Glutathione Peroxidase** (antioxidant) and **5'-deiodinase** (converts T4 to T3). * **Kashin-Beck Disease:** Another selenium deficiency disorder characterized by osteoarthropathy (cartilage degeneration). * **Viral Link:** Co-infection with the **Coxsackievirus B** is often implicated as a trigger that converts subclinical selenium deficiency into overt Keshan’s disease. * **Antidote:** Sodium selenite supplementation is used for prevention in endemic areas.

Question 104: Which amino acid is known to promote healing?

A. Alanine
B. Arginine (Correct Answer)
C. Glutamate
D. Glycine

Explanation: **Explanation:** **Arginine** is the correct answer because it plays a pivotal role in the metabolic processes required for tissue repair and wound healing. It serves as a precursor for two critical components: 1. **Nitric Oxide (NO):** Produced via the enzyme Nitric Oxide Synthase, NO enhances local vasodilation, increasing blood flow and oxygen delivery to the healing site. 2. **Proline and Polyamines:** Arginine is metabolized into proline (essential for **collagen synthesis**) and polyamines (essential for cell proliferation and protein synthesis). Additionally, arginine stimulates the release of anabolic hormones like growth hormone and insulin, further promoting a positive nitrogen balance. **Analysis of Incorrect Options:** * **Alanine:** Primarily functions as a key carrier of nitrogen from muscles to the liver via the Glucose-Alanine cycle. It is not a primary driver of structural tissue repair. * **Glutamate:** Acts as a major excitatory neurotransmitter and a precursor for GABA. While involved in general nitrogen metabolism, it lacks the specific vasodilatory and collagen-stimulating properties of arginine. * **Glycine:** Though it makes up one-third of the collagen structure, it is a non-essential amino acid readily synthesized by the body. In clinical nutrition, exogenous supplementation of arginine is prioritized over glycine for accelerating recovery. **Clinical Pearls for NEET-PG:** * **Conditionally Essential:** Arginine is considered "conditionally essential" because, during periods of severe stress, trauma, or sepsis, the body’s demand exceeds its biosynthetic capacity. * **Immunonutrition:** Arginine is a key component of "immunonutrition" formulas used in surgical ICUs to reduce post-operative infection rates. * **Urea Cycle:** Remember that Arginine is an intermediate in the Urea cycle and is cleaved by **Arginase** to produce Urea and Ornithine.

Question 105: What is the normal nitrogen content in 200 gm of protein?

A. 8 g
B. 16 g
C. 32 g (Correct Answer)
D. 64 g

Explanation: **Explanation:** The correct answer is **32 g**. **1. Underlying Concept:** In biochemistry and nutrition, it is a standard physiological principle that proteins contain an average of **16% nitrogen** by weight. This relationship is fundamental for calculating the Nitrogen Balance of a patient. To find the nitrogen content, we use the following formula: * **Nitrogen (g) = Protein (g) × 0.16** (or Protein ÷ 6.25) * Calculation: 200 g (Protein) × 0.16 = **32 g of Nitrogen**. **2. Analysis of Incorrect Options:** * **Option A (8 g):** This represents only 4% nitrogen content, which is incorrect for standard dietary proteins. * **Option B (16 g):** This is the nitrogen content of 100 g of protein (100 × 0.16). It is a common distractor for students who confuse the percentage (16%) with the absolute mass. * **Option D (64 g):** This represents 32% nitrogen content, which is double the physiological average. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **The 6.25 Factor:** The inverse of 16% (100/16) is **6.25**. In clinical practice, to estimate protein intake from urinary urea nitrogen, we multiply the nitrogen value by 6.25. * **Nitrogen Balance Formula:** $B = I - (U + F + S)$, where $I$ is nitrogen intake, $U$ is urinary loss, $F$ is fecal loss, and $S$ is skin loss. * **Positive Nitrogen Balance:** Seen during growth, pregnancy, and convalescence (recovery from illness). * **Negative Nitrogen Balance:** Seen in starvation, severe burns, high-grade fever, and uncontrolled diabetes mellitus. * **Kjeldahl Method:** This is the classic laboratory technique used to estimate the nitrogen content of biological samples.

Question 106: Which of the following minerals possesses antioxidant properties?

A. Calcium
B. Magnesium
C. Zinc (Correct Answer)
D. Iron

Explanation: ### Explanation **Correct Option: C (Zinc)** Zinc is a vital trace element that functions as an essential cofactor for over 300 enzymes. Its antioxidant properties are primarily attributed to its role as a structural component of **Copper-Zinc Superoxide Dismutase (Cu-Zn SOD)**, an enzyme that neutralizes superoxide radicals into hydrogen peroxide. Furthermore, Zinc induces the synthesis of **metallothioneins**, which are cysteine-rich proteins that scavenge hydroxyl radicals. It also protects protein sulfhydryl groups from oxidation and competes with pro-oxidant metals like iron and copper to prevent the formation of highly reactive free radicals via the Fenton reaction. **Why other options are incorrect:** * **A. Calcium:** Primarily functions in bone mineralization, muscle contraction, nerve impulse transmission, and as a secondary messenger (e.g., in the Calmodulin pathway). It does not possess intrinsic antioxidant activity. * **B. Magnesium:** Acts as a cofactor for enzymes involving ATP (kinases). While it is essential for metabolic stability, it is not classified as a primary antioxidant mineral. * **D. Iron:** Iron is actually a **pro-oxidant**. In its free form, it catalyzes the **Fenton reaction**, leading to the production of the highly damaging hydroxyl radical ($\cdot OH$). **High-Yield Clinical Pearls for NEET-PG:** * **Key Antioxidant Minerals:** Zinc, Selenium (cofactor for Glutathione Peroxidase), Copper, and Manganese. * **Zinc Deficiency:** Characterized by **Acrodermatitis enteropathica**, poor wound healing, hypogeusia (decreased taste), and growth retardation. * **Superoxide Dismutase (SOD) Isoforms:** * Cytosolic: Cu-Zn SOD * Mitochondrial: Mn-SOD (Manganese)

Question 107: What organ or tissue in the human body has the highest concentration of iodine?

A. Eggs
B. Fresh water fish
C. Thyroid gland (Correct Answer)
D. Poultry

Explanation: **Explanation:** **1. Why the Thyroid Gland is Correct:** The thyroid gland is the primary site for iodine storage and utilization in the human body. It possesses a unique physiological mechanism called the **Sodium-Iodide Symporter (NIS)**, which actively transports iodide from the blood into thyroid follicular cells against a steep concentration gradient. While the total body iodine content is approximately 15–20 mg, nearly **70–80%** of this is concentrated within the thyroid gland to synthesize thyroid hormones (T3 and T4). **2. Why the Other Options are Incorrect:** * **A, B, and D (Eggs, Fresh water fish, Poultry):** These are dietary sources of iodine, not tissues within the human body. While marine fish and eggs are excellent nutritional sources, they do not "concentrate" iodine to the physiological levels found in the human thyroid. Notably, saltwater fish generally contain higher iodine levels than freshwater fish. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Iodine Trapping:** This is the first step of thyroid hormone synthesis, stimulated by **TSH**. * **Wolff-Chaikoff Effect:** A transient reduction in thyroid hormone synthesis caused by the ingestion of a large amount of iodine. * **Daily Requirement:** The WHO recommends an iodine intake of **150 μg/day** for adults (higher in pregnancy: 250 μg/day). * **Ectopic Concentration:** Apart from the thyroid, iodine is also concentrated (though to a much lesser extent) in the salivary glands, gastric mucosa, and lactating mammary glands via the NIS, but these tissues cannot organify it into hormones. * **Radioactive Iodine (I-131):** Used clinically for thyroid scanning and ablation because of this specific concentration mechanism.

Question 108: How is protein best assessed?

A. Protein energy ratio
B. BUN
C. Per gram of calories given (Correct Answer)
D. Amino acid score

Explanation: **Explanation:** The assessment of protein utilization and adequacy is intrinsically linked to total energy intake. This concept is known as the **Protein-Sparing Action of Carbohydrates**. **Why the correct answer is right:** Protein is best assessed **per gram of calories given** because the body’s ability to utilize protein for tissue synthesis (anabolism) depends on meeting total caloric requirements. If energy intake is insufficient, the body oxidizes dietary protein to produce energy instead of using it for growth and repair. Therefore, the "Protein:Calorie ratio" (typically expressed as grams of protein per 100 kcal) is the most accurate clinical measure to ensure that protein is being used efficiently for its intended structural purposes. **Analysis of Incorrect Options:** * **Protein energy ratio (A):** While related, this is a general term. The specific measurement of protein relative to the total caloric density (Option C) is the standard for nutritional assessment. * **BUN (Blood Urea Nitrogen) (B):** This is a marker of protein catabolism and renal function, not a primary tool for assessing the adequacy of dietary protein intake. * **Amino acid score (D):** This measures the **quality** of a specific protein (based on its limiting amino acid) relative to a reference protein, but it does not assess the overall nutritional status or the adequacy of protein in a patient's total diet. **Clinical Pearls for NEET-PG:** * **Protein-Sparing Action:** Carbohydrates and fats "spare" proteins from being used as fuel. * **Nitrogen Balance:** The clinical gold standard for assessing net protein change in the body (Positive in growth/pregnancy; Negative in trauma/starvation). * **Reference Protein:** Egg protein (Biological Value = 100) is the standard against which others are compared. * **Limiting Amino Acids:** Pulses are deficient in Methionine; Cereals are deficient in Lysine.

Question 109: Which of the following are caused by zinc deficiency?

A. Mental retardation
B. Gonadal atrophy
C. Cardiomyopathy and reduced growth
D. Reduced growth and gonadal atrophy (Correct Answer)

Explanation: **Explanation:** Zinc is an essential trace element that acts as a cofactor for over 300 enzymes, including **Carbonic Anhydrase, Alcohol Dehydrogenase, and DNA/RNA polymerases**. It plays a critical role in protein synthesis, cell division, and nucleic acid metabolism, which are vital for growth and reproductive health. **Why Option D is correct:** * **Reduced Growth:** Zinc is indispensable for the synthesis of growth-related proteins and DNA. Deficiency leads to growth retardation and skeletal abnormalities. * **Gonadal Atrophy:** Zinc is essential for the maturation of the reproductive system and spermatogenesis. Deficiency results in hypogonadism, delayed puberty, and gonadal atrophy. **Analysis of Incorrect Options:** * **Option A (Mental Retardation):** While zinc deficiency can cause irritability or emotional lability, "Mental Retardation" is more characteristically associated with **Iodine deficiency** (Cretinism) or metabolic disorders like Phenylketonuria. * **Option B (Gonadal Atrophy):** While correct, it is an incomplete answer compared to Option D. * **Option C (Cardiomyopathy):** Cardiomyopathy is a classic hallmark of **Selenium deficiency** (Keshan disease), not zinc deficiency. **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder causing impaired zinc absorption, characterized by the triad of **alopecia, diarrhea, and vesiculobullous dermatitis** (periorificial and acral). * **Wound Healing:** Zinc is vital for collagen synthesis; deficiency leads to poor wound healing. * **Immunity:** Zinc deficiency causes thymic atrophy and impaired T-cell function. * **Dysgeusia:** A common symptom where the patient experiences a distorted sense of taste.

Question 110: Which of the following foods has the least glycemic index?

A. Baked potato
B. Brown rice (Correct Answer)
C. Ice cream
D. Whole white bread

Explanation: **Explanation:** The **Glycemic Index (GI)** is a ranking of carbohydrates on a scale of 0 to 100 based on how quickly they raise blood glucose levels after consumption. Foods with a low GI (≤ 55) are digested and absorbed slowly, causing a gradual rise in blood sugar. **Why Brown Rice is Correct:** Brown rice is a whole grain that retains its outer bran and germ layers. These layers are rich in **dietary fiber**, which acts as a physical barrier to digestive enzymes and slows down the hydrolysis of starch into glucose. Consequently, it has a lower GI (approx. 50–55) compared to refined grains and starchy tubers. **Analysis of Incorrect Options:** * **Baked Potato (GI ~85):** Cooking at high heat causes extensive **starch gelatinization**, making it extremely easy for pancreatic amylase to break down, leading to a rapid glucose spike. * **Whole White Bread (GI ~75):** Refined flour lacks fiber and has a high surface-area-to-volume ratio, allowing for rapid enzymatic digestion. * **Ice Cream (GI ~60-65):** While the fat content in ice cream slows gastric emptying (lowering GI slightly compared to pure sugar), its high sucrose content still results in a higher glycemic response than fiber-rich brown rice. **NEET-PG High-Yield Pearls:** 1. **Glycemic Load (GL):** A more accurate clinical predictor than GI, calculated as: $GL = \frac{GI \times \text{Net Carbohydrates (g)}}{100}$. 2. **Factors lowering GI:** High fiber content, presence of fat/protein, acidity (vinegar/lemon), and less processing. 3. **Clinical Relevance:** Low GI diets are the cornerstone of nutritional therapy for **Diabetes Mellitus Type 2**, PCOS, and metabolic syndrome to improve insulin sensitivity.

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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