Nutrition and Metabolism Practice Questions

Q: What is the minimum amount of protein required daily to achieve a positive nitrogen balance?

60 gm/day. **Explanation** The correct answer is **60 gm/day**. **1. Underlying Medical Concept** Nitrogen balance is the measure of nitrogen input (protein intake) minus nitrogen output (urea in urine, feces, and sweat). To achieve a **positive nitrogen balance**—where the body retains more nitrogen than it excretes—the intake must exceed the **obligatory nitrogen loss**. In a healthy adult weighing approximately 70 kg, the Recommended Dietary Allowance (RDA) for protein is **0.8 to 1.0 g/kg body weight/day**. This translates to roughly **56–70 gm/day**. At this level, the body can adequately perform tissue repair, enzyme synthesis, and growth. An intake of 60 gm/day ensures that the anabolic processes exceed catabolic breakdown, shifting the body into a positive nitrogen state. **2. Analysis of Incorrect Options** * **A (20-30 gm/day) & B (35-40 gm/day):** These amounts are below the minimum physiological requirement. At these levels, the body enters a **negative nitrogen balance**, leading to muscle wasting and protein-energy malnutrition (PEM) because obligatory losses exceed intake. * **C (50 gm/day):** While closer to the requirement, 50 gm is often considered the "bare minimum" to maintain equilibrium (zero balance) in smaller individuals, but it is insufficient to reliably ensure a *positive* balance in a standard adult population. **3. High-Yield Clinical Pearls for NEET-PG** * **Positive Nitrogen Balance:** Seen during growth, pregnancy, and recovery from illness/surgery. * **Negative Nitrogen Balance:** Seen in starvation, severe burns, sepsis, and uncontrolled diabetes. * **Biological Value (BV):** Egg protein has a BV of 100 and is the "Reference Protein." * **Kwashiorkor vs. Marasmus:** Kwashiorkor is a deficiency of protein despite adequate calories (presents with edema); Marasmus is a deficiency of both protein and total calories (presents with "skin and bones" appearance).

Q: Iron absorption is increased in which of the following conditions?

Iron deficiency anemia, Pregnancy. **Explanation:** Iron absorption is a tightly regulated process occurring primarily in the **duodenum and proximal jejunum**. The body’s iron status and erythropoietic demand are the primary regulators of this process. **Why Option C is Correct:** 1. **Iron Deficiency Anemia (IDA):** When body iron stores are low, the liver decreases the production of **Hepcidin** (the master regulator of iron). Low hepcidin levels allow for increased expression of **Ferroportin** on the basolateral membrane of enterocytes, facilitating greater iron transport into the blood. 2. **Pregnancy:** During pregnancy, there is a massive physiological demand for iron to support fetal growth, placental development, and increased maternal red cell mass. This state of "ineffective erythropoiesis" and high demand signals the body to suppress hepcidin, thereby maximizing intestinal iron absorption. **Analysis of Incorrect Options:** * **Malignancy (Options A, B, and D):** Chronic diseases, including malignancies and chronic infections, induce a state of inflammation. Inflammatory cytokines (specifically **IL-6**) stimulate the liver to **increase Hepcidin** production. High hepcidin levels degrade ferroportin, trapping iron inside macrophages and enterocytes, leading to **decreased** serum iron absorption (Anemia of Chronic Disease). **NEET-PG High-Yield Pearls:** * **Hepcidin:** It is an acute-phase reactant. High Hepcidin = Low Iron Absorption; Low Hepcidin = High Iron Absorption. * **Vitamin C (Ascorbic Acid):** Enhances iron absorption by reducing ferric ($Fe^{3+}$) iron to the more soluble ferrous ($Fe^{2+}$) form. * **Inhibitors of Absorption:** Phytates (cereals), Oxalates (spinach), Tannins (tea), and Calcium inhibit non-heme iron absorption. * **DMT-1 (Divalent Metal Transporter 1):** The primary transporter for apical entry of non-heme iron into the enterocyte.

Q: Colonic bacteria, upon digestion of dietary fibers, produce which of the following?

Butyrate. **Explanation:** The correct answer is **Butyrate**. Dietary fibers (non-starch polysaccharides like cellulose and pectin) are resistant to human digestive enzymes in the small intestine. Upon reaching the large intestine, they undergo anaerobic fermentation by the gut microbiota (colonic bacteria). This process primarily produces **Short-Chain Fatty Acids (SCFAs)**, specifically **Acetate, Propionate, and Butyrate.** * **Butyrate (Butyric acid):** This is the most significant SCFA for colonic health. It serves as the **primary fuel source for colonocytes** (epithelial cells of the colon) and plays a crucial role in maintaining mucosal integrity, inducing apoptosis in colon cancer cells, and exerting anti-inflammatory effects. **Why other options are incorrect:** * **Free radicals:** These are unstable molecules produced during oxidative stress or metabolic reactions; bacterial fermentation of fiber is generally a protective process that reduces oxidative damage. * **Glycerol:** This is a backbone of triglycerides, released during lipolysis (fat digestion), not fiber fermentation. * **Sucrose:** This is a disaccharide (table sugar) that is normally digested by sucrase in the small intestine into glucose and fructose. **NEET-PG High-Yield Pearls:** 1. **SCFA Ratio:** The typical molar ratio of SCFAs produced in the colon is Acetate (60%) > Propionate (25%) > Butyrate (15%). 2. **Metabolic Fates:** While Butyrate is used locally by colonocytes, **Propionate** travels to the liver for gluconeogenesis, and **Acetate** enters the peripheral circulation for cholesterol synthesis or oxidation in muscle. 3. **Prebiotics:** Dietary fibers are considered "prebiotics" because they selectively stimulate the growth of beneficial bacteria (like *Bifidobacterium*). 4. **Health Benefit:** High fiber intake is clinically linked to a decreased risk of colorectal cancer and diverticulosis due to these fermentation byproducts.

Q: Which of the following terms describes substances that supply carbohydrate polymers and also contain non-carbohydrate polymers that aid in digestion?

Dietary fibers. ### Explanation **1. Why Dietary Fibers is the Correct Answer:** 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. They primarily consist of **carbohydrate polymers** (such as cellulose, hemicellulose, and pectins) but crucially also contain **non-carbohydrate polymers**, most notably **lignin**. These substances aid in digestion by increasing fecal bulk, promoting peristalsis, and slowing the absorption of glucose and cholesterol. **2. Why the Other Options are Incorrect:** * **A. Monosaccharides:** These are the simplest form of carbohydrates (e.g., glucose, fructose). They are single units, not polymers, and do not contain non-carbohydrate components. * **B. Disaccharides:** These consist of two monosaccharide units (e.g., sucrose, lactose). Like monosaccharides, they are simple sugars and lack the complex structural non-carbohydrate polymers found in fiber. * **C. Polysaccharides:** While this is a broad category that includes starch and glycogen (digestible) as well as cellulose (indigestible), the term "polysaccharide" refers strictly to carbohydrate chains. It does not inherently account for the non-carbohydrate polymers (like lignin) specified in the question. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Lignin** is the only significant non-carbohydrate component of dietary fiber; it is a complex polymer of aromatic alcohols. * **Soluble vs. Insoluble:** Soluble fibers (pectins, gums) help lower LDL cholesterol; insoluble fibers (cellulose, lignin) prevent constipation. * **Short-Chain Fatty Acids (SCFAs):** Colonic bacteria ferment soluble fiber into SCFAs (acetate, propionate, butyrate), which provide energy to colonocytes and may prevent colon cancer. * **Recommended Intake:** The WHO recommends approximately **25–40g** of dietary fiber per day for adults.

Q: What is the energy generated from alcohol?

7 kcal/g. ### Explanation The energy content of food substances is determined by their caloric density, which represents the amount of energy released during complete oxidation. **1. Why 7 kcal/g is Correct:** Alcohol (Ethanol) is metabolized primarily in the liver. It undergoes oxidation by **Alcohol Dehydrogenase (ADH)** to acetaldehyde and then by **Aldehyde Dehydrogenase (ALDH)** to acetate. These reactions generate NADH, which enters the electron transport chain to produce ATP. The physiological fuel value of pure ethanol is approximately **7.1 kcal/g**, making it more energy-dense than carbohydrates but less than fats. **2. Analysis of Incorrect Options:** * **A. 4 kcal/g:** This is the physiological fuel value for **Carbohydrates and Proteins**. These are the primary sources of energy in a balanced diet. * **B. 0 kcal/g:** This applies to non-caloric substances like water, vitamins, minerals, and dietary fiber (cellulose), which do not provide metabolic energy. * **D. 9 kcal/g:** This is the caloric value of **Lipids (Fats)**. Fats are the most energy-dense macronutrients because they are highly reduced molecules. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Empty Calories:** Alcohol is often termed "empty calories" because it provides energy without essential nutrients (minerals/vitamins). * **MEOS Pathway:** In chronic alcoholics, the **Microsomal Ethanol Oxidizing System (CYP2E1)** is induced. This pathway is less energy-efficient as it utilizes NADPH, potentially leading to a lower net ATP yield compared to the ADH pathway. * **Metabolic Impact:** High alcohol intake increases the **NADH/NAD+ ratio**, which inhibits gluconeogenesis (leading to fasting hypoglycemia) and promotes fatty acid synthesis (leading to fatty liver/steatosis). * **Specific Dynamic Action (SDA):** Alcohol has a high thermic effect, meaning a significant portion of its energy is dissipated as heat.

Q: Menkes disease is due to deficiency of:

Copper. **Explanation:** **Menkes Disease (Kinky Hair Syndrome)** is an X-linked recessive disorder caused by a mutation in the **ATP7A gene**. This gene encodes a P-type ATPase protein responsible for the absorption of dietary copper from the intestine and its transport across the blood-brain barrier. In Menkes disease, copper is trapped within intestinal mucosal cells and cannot reach the systemic circulation, leading to severe **systemic copper deficiency**. **Why Copper is the Correct Answer:** Copper is a vital cofactor for several enzymes. Its deficiency leads to the clinical manifestations of Menkes disease: * **Lysyl Oxidase:** Impaired cross-linking of collagen and elastin (leads to arterial tortuosity and skeletal issues). * **Tyrosinase:** Failure of melanin synthesis (leads to hypopigmentation). * **Cytochrome c Oxidase:** Impaired oxidative phosphorylation (leads to neurodegeneration). * **Dopamine β-hydroxylase:** Impaired catecholamine synthesis. **Why Other Options are Incorrect:** * **Selenium:** Deficiency is associated with **Keshan disease** (cardiomyopathy) and Kashin-Beck disease (osteoarthritis). * **Chromium:** Deficiency leads to impaired glucose tolerance (insulin resistance) as chromium is a component of the Glucose Tolerance Factor (GTF). * **Manganese:** Deficiency is rare but can lead to impaired growth, skeletal abnormalities, and defects in carbohydrate/lipid metabolism. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Sign:** "Steely" or "Kinky" hair (pili torti) due to defective keratin disulfide bond formation. * **Diagnosis:** Low serum copper and low serum ceruloplasmin levels. * **Contrast with Wilson Disease:** Wilson disease involves the **ATP7B gene**, leading to copper **overload** (toxic accumulation) rather than deficiency. * **Inheritance:** X-linked Recessive (primarily affects males).

Q: In Protein Energy Malnutrition, which of the following immunoglobulins is most reduced?

IgA. **Explanation:** In Protein-Energy Malnutrition (PEM), such as Kwashiorkor and Marasmus, the immune system is significantly compromised, a state often referred to as "nutritionally acquired immunodeficiency." **Why IgA is the correct answer:** The most characteristic immunological defect in PEM is the reduction of **Secretory IgA (sIgA)**. This occurs due to the atrophy of mucosal surfaces and lymphoid tissues (like Peyer's patches). Since IgA is the primary mediator of mucosal immunity, its deficiency leads to a breakdown of the protective barrier in the respiratory and gastrointestinal tracts. This explains why children with PEM are highly susceptible to recurrent infections like pneumonia and infectious diarrhea. **Analysis of Incorrect Options:** * **IgG and IgM:** Interestingly, serum levels of IgG, IgM, and IgD are usually **normal or even elevated** in PEM. This is because the body maintains its ability to produce these systemic antibodies in response to the frequent underlying infections common in malnourished states. * **IgE:** Serum IgE levels are often **increased** in PEM, particularly in developing regions, primarily due to the high prevalence of co-existing parasitic (helminthic) infestations. **High-Yield Clinical Pearls for NEET-PG:** * **Cell-Mediated Immunity (CMI):** This is the most severely affected component of the immune system in PEM. There is marked **thymic atrophy**, reduced T-cell counts, and a negative Mantoux test (anergy) even in the presence of TB. * **Complement System:** Levels of most complement components (except C4) are significantly reduced. * **Phagocytosis:** While the number of neutrophils is usually normal, their **bactericidal activity** (oxidative burst) is impaired.

Question 1

Copper deficiency manifests as which of the following?

Accepted Answer

Anaemia

Answer

Cardiomyopathy

Answer

Hepatomegaly

Answer

Hypothyroidism

Question 2

What is the minimum amount of protein required daily to achieve a positive nitrogen balance?

Accepted Answer

60 gm/day

Answer

20-30 gm/day

Answer

35-40 gm/day

Answer

50 gm/day

Question 3

Iron absorption is increased in which of the following conditions?

Accepted Answer

Iron deficiency anemia, Pregnancy

Answer

Iron deficiency anemia, Malignancy

Answer

Pregnancy, Malignancy

Answer

Iron deficiency anemia, Pregnancy, Malignancy

Question 4

Colonic bacteria, upon digestion of dietary fibers, produce which of the following?

Accepted Answer

Butyrate

Answer

Free radicals

Answer

Glycerol

Answer

Sucrose

Question 5

Which of the following terms describes substances that supply carbohydrate polymers and also contain non-carbohydrate polymers that aid in digestion?

Accepted Answer

Dietary fibers

Answer

Monosaccharide

Answer

Disaccharide

Answer

Polysaccharide

Question 6

Which of the following is most commonly used to assess protein utilization?

Accepted Answer

Net protein utilization (NPU)

Answer

Amino acid score

Answer

Biological value

Answer

Protein efficiency ratio

Question 7

What is the energy generated from alcohol?

Accepted Answer

7 kcal/g

Answer

4 kcal/g

Answer

0 kcal/g

Answer

9 kcal/g

Question 8

Menkes disease is due to deficiency of:

Accepted Answer

Copper

Answer

Selenium

Answer

Chromium

Answer

Manganese

Question 9

In Protein Energy Malnutrition, which of the following immunoglobulins is most reduced?

Accepted Answer

IgA

Answer

IgG

Answer

IgM

Answer

IgE

Question 10

Intake of a high protein diet causes which of the following?

Accepted Answer

Increased gluconeogenesis

Answer

Increased beta oxidation

Answer

Decreased glycogenolysis

Answer

Metabolic alkalosis

Nutrition and Metabolism — MCQs

Nutrition and Metabolism — MCQs

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