Nutrition and Metabolism Practice Questions

Q: Which of the following is the important reactive group of glutathione in its role as an antioxidant?

Sulphydryl. **Explanation:** **Glutathione (GSH)** is a tripeptide composed of three amino acids: **Glutamate, Cysteine, and Glycine**. It serves as the body’s premier endogenous antioxidant, protecting cells from oxidative stress caused by reactive oxygen species (ROS) like hydrogen peroxide ($H_2O_2$). 1. **Why Sulphydryl is Correct:** The functional "business end" of glutathione is the **sulphydryl (–SH) group** provided by the amino acid **Cysteine**. In its reduced state (GSH), the –SH group acts as an electron donor to neutralize free radicals. During this process, two molecules of GSH are oxidized to form a disulfide-linked dimer (GSSG). The enzyme **Glutathione Peroxidase** facilitates this reaction, while **Glutathione Reductase** regenerates GSH using NADPH as a cofactor. 2. **Why Other Options are Incorrect:** * **Serine:** Contains a hydroxyl (–OH) group, not a thiol group, and is not a component of glutathione. * **Tyrosine:** An aromatic amino acid involved in signaling and hormone synthesis (e.g., Thyroxine, Catecholamines), but it does not provide the redox potential required for glutathione’s function. * **Acetyl-CoA:** This is a central metabolic intermediate in the TCA cycle and fatty acid synthesis, not a structural component of glutathione. **Clinical Pearls for NEET-PG:** * **NADPH Source:** The NADPH required to keep glutathione in its reduced state is primarily supplied by the **HMP Shunt (G6PD enzyme)**. * **G6PD Deficiency:** A deficiency in G6PD leads to low NADPH, resulting in oxidized glutathione. This leaves RBCs vulnerable to oxidative damage, leading to **Heinz bodies** and hemolytic anemia. * **Paracetamol Poisoning:** N-acetylcysteine (NAC) is the antidote for acetaminophen toxicity because it replenishes glutathione stores by providing cysteine.

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

Egg. **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.

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

Fats, Alcohol, Carbohydrate. **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.

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

Diabetes. **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**.

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: 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 one among the following is not an antioxidant?

Iron. ### Explanation The correct answer is **Iron (D)**. While many minerals act as essential components of the body’s antioxidant defense system, Iron is primarily considered a **pro-oxidant** in its free form. **Why Iron is the Correct Answer:** Free iron ($Fe^{2+}$) participates in the **Fenton Reaction**, where it reacts with hydrogen peroxide ($H_2O_2$) to generate the **hydroxyl radical (•OH)**. The hydroxyl radical is the most reactive and damaging reactive oxygen species (ROS), causing lipid peroxidation and DNA damage. Therefore, rather than preventing oxidative stress, excess free iron promotes it. **Why the other options are incorrect:** * **Selenium (B):** A vital antioxidant mineral. It is a mandatory cofactor for **Glutathione Peroxidase**, the enzyme responsible for neutralizing hydrogen peroxide into water. * **Zinc (A) and Copper (C):** Both are essential structural and catalytic components of **Cytosolic Superoxide Dismutase (Cu-Zn SOD)**. This enzyme dismutates the superoxide radical ($O_2^{•-}$) into less harmful hydrogen peroxide. Zinc also protects protein sulfhydryl groups from oxidation. **High-Yield Clinical Pearls for NEET-PG:** * **Manganese (Mn):** Acts as a cofactor for **Mitochondrial SOD**. * **Haber-Weiss Reaction:** Another pathway where iron (or copper) facilitates the formation of hydroxyl radicals from superoxide and hydrogen peroxide. * **Clinical Correlation:** In conditions like **Hemochromatosis** (iron overload), the massive production of free radicals via the Fenton reaction leads to tissue damage (cirrhosis, bronze diabetes). * **Antioxidant Vitamins:** Remember the mnemonic **"ACE"** (Vitamins A, C, and E). Vitamin E is the most potent chain-breaking antioxidant in lipid membranes.

Q: The nitrogen content in 50 gm of a typical dietary protein is most likely to be?

8 gm. **Explanation:** The nitrogen content of a typical dietary protein is a fundamental concept in nutritional biochemistry, specifically in the calculation of **Nitrogen Balance**. **1. Why Option B (8 gm) is Correct:** On average, dietary proteins contain approximately **16% nitrogen** by weight. This is a standard biological constant used in clinical medicine. To find the nitrogen content in 50 gm of protein, the calculation is: * $50 \text{ gm (Protein)} \times 0.16 \text{ (16\%)} = \mathbf{8 \text{ gm of Nitrogen}}$ Conversely, if the nitrogen content is known, the protein amount can be calculated using the **protein factor of 6.25** ($100/16 = 6.25$). For example, $8 \text{ gm Nitrogen} \times 6.25 = 50 \text{ gm Protein}$. **2. Why Other Options are Incorrect:** * **Option A (5 gm):** This represents only 10% nitrogen content, which is too low for standard dietary proteins. * **Option C (10 gm):** This represents 20% nitrogen content. While some specific amino acids (like Arginine) are nitrogen-rich, the average for mixed dietary protein remains 16%. * **Option D (16 gm):** This is a common "distractor" value because 16 is the percentage used in the calculation ($16\%$), not the absolute weight in grams for a 50 gm sample. **Clinical Pearls & High-Yield Facts:** * **Nitrogen Balance Equation:** $\text{Nitrogen Balance} = \text{Nitrogen Intake} - (\text{Urinary Urea Nitrogen} + 4)$. (The '+4' accounts for insensible losses via skin and feces). * **Positive Nitrogen Balance:** Seen during growth, pregnancy, and recovery from illness (anabolic states). * **Negative Nitrogen Balance:** Seen in starvation, severe burns, sepsis, and high-fever (catabolic states). * **Kjeldahl Method:** The standard laboratory technique used to determine the nitrogen content of organic substances.

Question 1

Which of the following is the important reactive group of glutathione in its role as an antioxidant?

Accepted Answer

Sulphydryl

Answer

Serine

Answer

Tyrosine

Answer

Acetyl-CoA

Question 2

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

Accepted Answer

Egg

Answer

Fish

Answer

Pulses

Answer

Chicken

Question 3

Which of the following statements are true about dietary fiber?

Accepted Answer

Dietary fiber increases GI transit time.

Answer

Soluble fiber increases the metabolism of sugar in the GIT.

Answer

Dietary fiber increases the bulk of stool.

Answer

Only soluble fibers are included in the diet.

Question 4

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

Accepted Answer

Fats, Alcohol, Carbohydrate

Answer

Carbohydrate, Fats, Alcohol

Answer

Alcohol, Carbohydrate, Fats

Answer

Alcohol, Fats, Carbohydrate

Question 5

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

Accepted Answer

Diabetes

Answer

Hypertension

Answer

Children

Answer

Normal adults

Question 6

Copper deficiency manifests as which of the following?

Accepted Answer

Anaemia

Answer

Cardiomyopathy

Answer

Hepatomegaly

Answer

Hypothyroidism

Question 7

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 8

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

Accepted Answer

Butyrate

Answer

Free radicals

Answer

Glycerol

Answer

Sucrose

Question 9

Which one among the following is not an antioxidant?

Accepted Answer

Iron

Answer

Zinc

Answer

Selenium

Answer

Copper

Question 10

The nitrogen content in 50 gm of a typical dietary protein is most likely to be?

Accepted Answer

8 gm

Answer

5 gm

Answer

10 gm

Answer

16 gm

Nutrition and Metabolism — MCQs

Nutrition and Metabolism — MCQs

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