Protein Quality and Nitrogen Balance — MCQs
Protein metabolism after trauma is characterized by the following except:
In which of the following conditions is protein catabolism MOST increased?
Which of the following is NOT a finding within 24 hours of starvation in a 19-year-old patient with Anorexia Nervosa?
In a patient with maple syrup urine disease, all of the following amino acids should be restricted in diet except?
A 32-year-old male is on a weight-maintenance diet, so he does not want to lose or gain any weight. Which amino acid must be present in the diet to prevent the patient from going into a negative nitrogen balance?
What is the best method to estimate the amount of proteinuria in a 2-year-old child with nephrotic syndrome?
Biological value is used for the assessment of?
Which one among the following essential amino acids is usually the "limiting" amino acid in most of the pulses?
Which of the following protein sources has the lowest biological value?
Protein quality assessment is best done by?
Protein Quality and Nitrogen Balance Indian Medical PG Practice Questions and MCQs
Question 1: Protein metabolism after trauma is characterized by the following except:
- A. Increased liver gluconeogenesis
- B. Increased urinary nitrogen loss
- C. Hepatic synthesis of acute phase reactants
- D. Inhibition of skeletal muscle breakdown by interleukin 1 and tumour necrosis factor (Correct Answer)
Explanation: ***Inhibition of skeletal muscle breakdown by interleukin 1 and tumour necrosis factor*** - After trauma, **interleukin 1 (IL-1)** and **tumor necrosis factor (TNF)** actually **promote** skeletal muscle breakdown (catabolism) to provide amino acids for gluconeogenesis and acute phase protein synthesis. - This statement is incorrect because these cytokines are **pro-catabolic**, not inhibitory, in their effect on muscle protein. *Increased liver gluconeogenesis* - Trauma leads to a significant increase in **liver gluconeogenesis**, primarily to maintain glucose supply for **immune cells** and wound healing, which rely heavily on glucose. - This process utilizes amino acids obtained from muscle breakdown as substrates. *Increased urinary nitrogen loss* - The breakdown of muscle protein releases amino acids, which are then deaminated. The nitrogen waste product, **urea**, is excreted in the urine, leading to **increased urinary nitrogen loss**. - This is a direct consequence of the catabolic state. *Hepatic synthesis of acute phase reactants* - The liver increases the synthesis of **acute phase reactants** (e.g., C-reactive protein, fibrinogen, haptoglobin) in response to inflammatory cytokines like IL-1, **IL-6**, and TNF. - These proteins play a crucial role in the inflammatory response and tissue repair.
Question 2: In which of the following conditions is protein catabolism MOST increased?
- A. Burns (Correct Answer)
- B. Surgery
- C. Starvation
- D. Fever
Explanation: ***Burns*** - Severe burns lead to a profound **hypermetabolic state** with the highest increase in **protein catabolism** among all the options listed. - The extensive tissue damage triggers massive breakdown of muscle protein to provide amino acids for **wound healing**, **acute phase protein synthesis**, and **immune response**. - Burns can increase metabolic rate by **100-200%**, with protein catabolism far exceeding that of other stress conditions. *Starvation* - While starvation initially increases protein catabolism, the body adapts within days by shifting towards **ketone body utilization** to spare protein. - After adaptation, protein breakdown decreases to **20-30 grams per day** to preserve lean body mass. - The goal is survival through metabolic adaptation, not tissue repair. *Surgery* - Major surgery induces a **stress response** that increases protein catabolism, but it is typically less severe and shorter-lived than burns. - The degree of catabolism is proportional to the **magnitude of surgical trauma** and usually resolves within days. - Protein catabolism increases by **50-75%** in major surgery compared to **100-200%** in severe burns. *Fever* - Fever increases basal metabolic rate by approximately **13% per degree Celsius** rise in body temperature. - While metabolism is elevated, protein catabolism is **modest** compared to the massive tissue destruction and repair demands of severe burns. - The increase is primarily in energy expenditure, not protein breakdown.
Question 3: Which of the following is NOT a finding within 24 hours of starvation in a 19-year-old patient with Anorexia Nervosa?
- A. Decrease in serum proteins (Correct Answer)
- B. Decrease in glycogen
- C. Increase in free fatty acids
- D. Increase in ketone bodies
Explanation: ***Decrease in serum proteins*** - **Serum protein levels** generally decrease only after a prolonged period of starvation (weeks to months), as the body initially catabolizes proteins from less vital tissues. - In the **initial 24 hours of starvation**, the body primarily relies on glycogenolysis and lipolysis, with significant protein breakdown occurring later. *Increase in free fatty acids* - Within **24 hours of starvation**, the body switches from carbohydrate metabolism to fat utilization due to declining insulin and rising glucagon levels. - This leads to increased **lipolysis** in adipose tissue, releasing **free fatty acids** into circulation to be used as fuel. *Increase in ketone bodies* - As **free fatty acid** levels rise, the liver converts them into **ketone bodies** (beta-hydroxybutyrate and acetoacetate) which become an important energy source for tissues like the brain during starvation. - This process, known as **ketogenesis**, accelerates within the first 24 hours to 3 days of food deprivation. *Decrease in glycogen* - The body's primary immediate energy reserve, **glycogen** (stored in the liver and muscles), is rapidly depleted within the first **12-24 hours of starvation** through **glycogenolysis**. - Liver glycogen is particularly crucial for maintaining blood glucose levels during this initial phase.
Question 4: In a patient with maple syrup urine disease, all of the following amino acids should be restricted in diet except?
- A. Methionine (Correct Answer)
- B. Isoleucine
- C. Leucine
- D. Valine
Explanation: ***Methionine*** - **Maple syrup urine disease (MSUD)** is a disorder affecting the metabolism of **branched-chain amino acids (BCAAs)**: leucine, isoleucine, and valine. - Therefore, methionine, which is not a BCAA, typically does not need to be restricted and is, in fact, an **essential amino acid** crucial for protein synthesis. *Isoleucine* - **Isoleucine** is a branched-chain amino acid (BCAA) whose metabolism is impaired in MSUD due to a deficiency in **branched-chain alpha-keto acid dehydrogenase complex**. - Accumulation of isoleucine and its corresponding alpha-keto acid is toxic and must be **restricted in the diet**. *Leucine* - **Leucine** is another branched-chain amino acid (BCAA) that cannot be properly metabolized in MSUD. - High levels of leucine and its metabolites are particularly **neurotoxic** and contribute to the characteristic neurological symptoms, necessitating strict dietary restriction. *Valine* - **Valine** is the third branched-chain amino acid (BCAA) whose breakdown is defective in MSUD. - Dietary restriction of valine is essential to prevent its accumulation, which can lead to metabolic crises and **developmental delays**.
Question 5: A 32-year-old male is on a weight-maintenance diet, so he does not want to lose or gain any weight. Which amino acid must be present in the diet to prevent the patient from going into a negative nitrogen balance?
- A. Alanine
- B. Arginine
- C. Glycine
- D. Threonine (Correct Answer)
Explanation: ***Threonine*** - **Threonine** is an **essential amino acid**, meaning the body cannot synthesize it and it must be obtained from the diet. - To maintain a **neutral nitrogen balance** and prevent a **negative nitrogen balance** (loss of body protein), all essential amino acids, including threonine, must be supplied in adequate amounts. *Alanine* - **Alanine** is a **non-essential amino acid**, which means the body can synthesize it from other compounds; therefore, its absence from the diet would not directly cause a negative nitrogen balance. - It plays a significant role in **gluconeogenesis** and the **glucose-alanine cycle**. *Arginine* - **Arginine** is considered a **conditionally essential amino acid**, meaning it can be synthesized by the body, but sometimes not in sufficient amounts to meet needs (e.g., during rapid growth, illness, or trauma). - Under normal weight-maintenance conditions, the body can typically synthesize enough arginine. *Glycine* - **Glycine** is a **non-essential amino acid** and is the smallest amino acid, often easily synthesized by the body. - Its presence in the diet, while important, is not critical for preventing negative nitrogen balance because the body can produce it.
Question 6: What is the best method to estimate the amount of proteinuria in a 2-year-old child with nephrotic syndrome?
- A. Single morning spot urine sample for protein/creatinine ratio (Correct Answer)
- B. 24 hr urine protein
- C. Dipstick testing
- D. Microalbuminuria
Explanation: ***Single morning spot urine sample for protein/creatinine ratio*** - The **protein/creatinine ratio** in a single morning spot urine sample correlates well with 24-hour urine protein excretion and is more convenient, especially in children. - This method avoids the difficulties associated with **24-hour urine collection** in young children, such as incomplete or inaccurate collection. *24 hr urine protein* - While considered the gold standard, **24-hour urine collection** is often impractical and unreliable in a 2-year-old due to challenges in complete collection. - Incomplete collections can lead to **underestimation** of proteinuria, making the result inaccurate for diagnosis and monitoring. *Dipstick testing* - **Dipstick testing** provides a qualitative or semi-quantitative estimate of proteinuria but can be affected by urine concentration and pH. - It lacks the precision needed to accurately quantify proteinuria for monitoring treatment response or assessing disease severity in **nephrotic syndrome**. *Microalbuminuria* - **Microalbuminuria** refers specifically to the excretion of albumin in amounts too small to be detected by standard dipstick tests but higher than normal. - This test is primarily used for early detection of **diabetic nephropathy** and is not the primary method for quantifying overt proteinuria in nephrotic syndrome.
Question 7: Biological value is used for the assessment of?
- A. Fat quality
- B. Protein quality (Correct Answer)
- C. Carbohydrate quality
- D. None of the options
Explanation: ***Protein quality*** - **Biological value (BV)** is a measure of the proportion of absorbed protein from a food that is incorporated into the body's proteins. - It specifically assesses the amount and **proportions of essential amino acids** available for protein synthesis. *Fat quality* - Fat quality is typically assessed by its **fatty acid profile** (e.g., saturated, unsaturated, trans fats) and its impact on cardiovascular health. - BV is not used to evaluate the nutritional quality or absorption of lipids. *Carbohydrate quality* - Carbohydrate quality is generally determined by factors like **fiber content**, **glycemic index**, and presence of complex vs. simple sugars. - BV does not provide information about the carbohydrate composition or metabolic effects of foods. *None of the options* - This option is incorrect because biological value is a well-established method for assessing protein quality.
Question 8: Which one among the following essential amino acids is usually the "limiting" amino acid in most of the pulses?
- A. Valine
- B. Threonine
- C. Methionine (Correct Answer)
- D. Lysine
Explanation: ***Methionine*** - In **pulses** (legumes), the sulfur-containing amino acids, primarily **methionine** and **cysteine**, are often the first limiting amino acids. - This means that the amount of protein synthesis that can occur is restricted by the availability of methionine, even if other essential amino acids are abundant. *Valine* - **Valine** is an essential branched-chain amino acid, but it is typically not the limiting amino acid in pulses. - It is more likely to be limiting in certain grains or in specific diets lacking a variety of protein sources. *Threonine* - **Threonine** is an essential amino acid that can be limiting in some cereals, but it is not typically the primary limiting amino acid in pulses. - Its deficiency is less common in a balanced diet including legumes. *Lysine* - **Lysine** is often the limiting amino acid in most **cereal grains** (e.g., wheat, corn, rice). - Pulses, however, are generally good sources of lysine, making its deficiency less likely when consumed.
Question 9: Which of the following protein sources has the lowest biological value?
- A. Gelatin (Correct Answer)
- B. Albumin
- C. Cashewnut protein
- D. Lactalbumin
Explanation: ***Gelatin*** - Gelatin is derived from collagen and is notably deficient in several **essential amino acids**, particularly **tryptophan**. - Its incomplete amino acid profile gives it a very **low biological value**, meaning it's poorly utilized by the body for protein synthesis. *Lactalbumin* - Lactalbumin is a **whey protein** found in milk, known for its **high biological value**. - It contains a **complete profile of essential amino acids** and is easily digestible. *Albumin* - Albumin, typically referring to **egg albumin** (egg white protein) or **serum albumin**, has an **excellent biological value**. - It is often used as a reference protein due to its well-balanced and **complete amino acid composition**. *Cashewnut protein* - While nuts like cashews provide protein, they generally have a **moderate to high biological value**, though typically not as high as animal proteins. - Cashew protein contains a good range of amino acids but might be slightly limited in one or two essential amino acids compared to a reference like egg or whey.
Question 10: Protein quality assessment is best done by?
- A. NPU (Correct Answer)
- B. Biological value
- C. Amino acid score
- D. Digestibility coefficient
Explanation: ***NPU*** - **Net Protein Utilization (NPU)** is considered the best method for assessing protein quality because it measures the percentage of ingested protein that is actually retained and utilized by the body. - It accounts for both the **digestibility** of the protein and the **biological value** of the absorbed amino acids, providing a comprehensive assessment. *Biological value* - **Biological Value (BV)** measures the proportion of absorbed protein from food that becomes incorporated into proteins in the organism's body. - While important, BV does not account for the **digestibility** of the protein, meaning some protein may not be absorbed even if its amino acid profile is excellent. *Digestibility coefficient* - The **digestibility coefficient** measures the proportion of food protein that is absorbed from the gastrointestinal tract. - It only reflects the extent of **absorption** and does not provide information about how efficiently the absorbed amino acids are utilized once inside the body for protein synthesis. *Amino acid score* - The **amino acid score** compares the amino acid profile of a test protein with the amino acid requirements of humans. - This score identifies the **limiting amino acid** but does not factor in the protein's digestibility or how effectively the absorbed amino acids are used by the body.
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