Chapter 1 - Fuel Metabolism and Nutrition: Basic Principles Flashcards
The largest amount of stored energy in the body (A) Protein (B) Triacylglycerol (C) Liver glycogen (D) Muscle glycogen
The answer is B. Adipose triacylglycerols contain the largest amount of stored energy in humans, followed by protein (even though loss of too much protein will lead to death), muscle glycogen, and liver glycogen (see Table 1.1).
The energy source reserved for strenuous muscular activity (A) Protein (B) Triacylglycerol (C) Liver glycogen (D) Muscle glycogen
The answer is D. Muscle glycogen is used for energy during exercise. The glycogen is degraded to a form of glucose that can enter metabolic pathways for energy generation. Because exercise is strenuous, muscle requires large amounts of energy, and this can be generated at the fastest rate by converting muscle glycogen to pathway precursors within the muscle. Liver glycogen will produce glucose that enters the circulation. Once in the circulation, the muscle can take up that glucose and use it to generate energy; however, the rate of energy generation from liver-derived glucose is much slower than that from muscle-derived glucose.
The primary source of carbon for maintaining blood glucose levels during an overnight fast (A) Protein (B) Triacylglycerol (C) Liver glycogen (D) Muscle glycogen
The answer is C. Liver glycogenolysis is the major process for maintaining blood glucose levels after an overnight fast. The muscle cannot export glucose to contribute to the maintenance of blood glucose levels, and fatty acid carbons cannot be utilized for the net synthesis of glucose.
The major precursor of urea in the urine (A) Protein (B) Triacylglycerol (C) Liver glycogen (D) Muscle glycogen
The answer is A. The nitrogen in amino acids derived from protein is converted to urea and excreted in the urine. Uric acid, another excretion product that contains nitrogen, is derived from purine bases (found in nucleic acids), not from protein.
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 so the patient does not go into a negative nitrogen balance? (A) Alanine (B) Arginine (C) Glycine (D) Threonine (E) Serine
The answer is D. The lack of one essential amino acid will lead to a negative nitrogen balance due to increased protein degradation to supply that amino acid for the ongoing protein synthesis. Of the amino acids listed, only threonine is an essential amino acid (alanine can be synthesized from pyruvate [which can be derived from glucose], arginine is produced in the urea cycle using aspartic acid and the amino acid ornithine, glycine is derived from serine, and serine is derived from 3-phosphoglycerate, which can be produced from glucose).
After a fast of a few days, ketone bodies become an important fuel (A) Liver (B) Brain (C) Skeletal muscle (D) Red blood cells
The answer is B. The brain begins to use ketone bodies when levels start to rise after
3 to 5 days of fasting. Normally, the brain will use only glucose as a fuel (most fatty acids cannot cross the blood–brain barrier to be metabolized by the brain), but when ketone bodies are elevated in the blood, they can enter the brain and be used for energy.
Ketone bodies are used as a fuel after an overnight fast (A) Liver (B) Brain (C) Skeletal muscle (D) Red blood cells
The answer is C. Skeletal muscle oxidizes ketone bodies, which are synthesized in the liver from fatty acids derived from adipose tissue. As the fast continues, the muscle will switch to oxidizing fatty acids, which allows ketone body levels to rise such that the brain will begin using them as an energy source.
Fatty acids are not a significant fuel source at any time (A) Liver (B) Brain (C) Skeletal muscle (D) Red blood cells
The answer is D. Oxidation of fatty acids occurs in mitochondria. Red blood cells lack mitochondria and therefore cannot use fatty acids. The brain will not transport most fatty acids across the blood–brain barrier (the essential fatty acids are a notable exception). Therefore, the brain cannot use fatty acids as an energy source. The brain does, however, synthesize its own fatty acids, and will oxidize those fatty acids when appropriate. Red blood cells can never use fatty acids as an energy source due to their lack of mitochondria.
During starvation, this tissue uses amino acids to maintain blood glucose levels (A) Liver (B) Brain (C) Skeletal muscle (D) Red blood cells
The answer is A. The liver converts amino acids to blood glucose by gluconeogenesis. The other substrates for gluconeogenesis are lactate from the metabolism of glucose within the red blood cells and glycerol from the breakdown of triacylglycerol to free fatty acids and glycerol. Neither the brain, nor the skeletal muscle, nor the red blood cell can export glucose into the circulation.
This tissue converts lactate from muscle to a fuel for other tissues (A) Liver (B) Brain (C) Skeletal muscle (D) Red blood cells
The answer is A. Exercising muscle produces lactate, which the liver can convert to glucose by gluconeogenesis. Blood glucose is oxidized by red blood cells and other tissues. Only the liver and kidney (to a small extent) can release free glucose into the circulation for use by other tissues.
A young woman (5’ 3” tall, 1.6 m) who has a sedentary job and does not exercise consulted a physician about her weight, which was 110 lb (50 kg). A dietary history indicates that she eats approximately 100 g of carbohydrate, 20 g of protein, and 40 g of fat daily.
What is this woman’s BMI? (A) 16.5 (B) 17.5 (C) 18.5 (D) 19.5 (E) 20.5
The answer is D. The BMI is calculated by dividing the weight of the individual (in kilograms) by the square of the height of the individual (in meters). For this woman, BMI 5 50/1.62 5 19.5.
A young woman (5’ 3” tall, 1.6 m) who has a sedentary job and does not exercise consulted a physician about her weight, which was 110 lb (50 kg). A dietary history indicates that she eats approximately 100 g of carbohydrate, 20 g of protein, and 40 g of fat daily.
According to the woman’s BMI, into what classification does her weight and height place her? (A) Underweight (B) Normal range (C) Overweight (preobese) (D) Class I obese range (E) Class II obese range
The answer is B. According to Table 1.2, a BMI of 19.5 places the woman at the lower end of the normal range. Underweight is indicated by a BMI of <18.5; preobesity occurs above a BMI of 25, but <30. Class I obesity is indicated by a BMI between 30 and 35, and class II obesity by a BMI between 35 and 40.
A young woman (5’ 3” tall, 1.6 m) who has a sedentary job and does not exercise consulted a physician about her weight, which was 110 lb (50 kg). A dietary history indicates that she eats approximately 100 g of carbohydrate, 20 g of protein, and 40 g of fat daily.
How many calories (kcal) does this woman consume each day? (A) 1,440 (B) 1,340 (C) 940 (D) 840 (E) 640
The answer is D. The woman consumes 400 calories (kcal) of carbohydrate (100 g x 4 kcal/g), 80 calories of protein (20 x 4), and 360 calories of fat (40 x 9) for a total of 840 calories daily.
A young woman (5’ 3” tall, 1.6 m) who has a sedentary job and does not exercise consulted a physician about her weight, which was 110 lb (50 kg). A dietary history indicates that she eats approximately 100 g of carbohydrate, 20 g of protein, and 40 g of fat daily.
What is the woman’s approximate DEE in calories (kilocalories) per day at this weight? (A) 1,200 (B) 1,560 (C) 1,800 (D) 2,640 (E) 3,432
The answer is B. This woman’s DEE is 1,560 calories (kcal). DEE equals BMR plus physical activity. Her weight is 110 lb/2.2 5 50 kg. Her BMR (about 24 kcal/kg) is 50 kg 3 24 5 1,200 kcal/day. She is sedentary and needs only 360 additional kcal (30% of her BMR) to support her physical activity. Therefore, she needs 1,200 1 360 5 1,560 kcal each day.
A young woman (5’ 3” tall, 1.6 m) who has a sedentary job and does not exercise consulted a physician about her weight, which was 110 lb (50 kg). A dietary history indicates that she eats approximately 100 g of carbohydrate, 20 g of protein, and 40 g of fat daily.
On the basis of the woman’s current weight, diet, and sedentary lifestyle, which one of the following does the physician correctly recommend that she should undertake?
(A) Increase her exercise level
(B) Decrease her protein intake
(C) Increase her caloric intake
(D) Decrease her fat intake to ,30% of her
total calories
(E) Decrease her caloric intake
The answer is C. Because her caloric intake (840 kcal/day) is less than her expenditure
(1,560 kcal/day), the woman is losing weight. She needs to increase her caloric intake. Exercise would cause her to lose more weight. She is probably in negative nitrogen balance because her protein intake is low (0.8 g/kg/day is recommended). Although her fat intake is 43% of her total calories and recommended levels are <30%, she should increase her total calories by increasing her carbohydrate and protein intake rather than decreasing her fat intake.
Consider a normal 25-year-old man, about 70 kg in weight, who has been shipwrecked
on a desert island, with no food available, but plenty of freshwater. Which of the following fuel stores is least likely to provide significant calo- ries to the man?
(A) Adipose triacylglycerol
(B) Liver glycogen
(C) Muscle glycogen
(D) Muscle protein
(E) Adipose triacylglycerol and liver glycogen
The answer is B. As indicated in Table 1.1, in the average (70 kg) man, adipose tissue contains 15 kg of fat or 135,000 calories (kcal). Liver glycogen contains about 0.08 kg of carbohydrate (320 calories), and muscle glycogen contains about 0.15 kg of carbohydrate (600 calories). In addition, about 6 kg of muscle protein (24,000 calories) can be used as fuel. Therefore, liver glycogen contains the fewest available calories.
The shipwrecked man described in the previous question will have most of his fuel stored as triacylglycerol instead of protein in muscle due to triacylglycerol stores containing which of the following as compared to protein stores? (A) More calories and more water (B) Less calories and less water (C) Less calories and more water (D) More calories and less water (E) Equal calories and less water
The answer is D. Adipose tissue contains more calories (kilocalories) and less water than does muscle protein. Triacylglycerol stored in adipose tissue contains 9 kcal/g, and adipose tissue has about 15% water. Muscle protein contains 4 kcal/g and has about 80% water.
A vegan has been eating low-quality vegetable protein for many years, and is now exhibiting a negative nitrogen balance. This may be occurring due to a lack of which one of the following in his/her diet? (A) Linoleic acid (B) Starch (C) Serine (D) Lysine (E) Linolenic acid
The answer is D. A negative nitrogen balance will result from a diet deficient in one essential amino acid, or in a very diseased state. Linoleic and linolenic acids are the essential fatty acids in the diet, and a lack of these fatty acids will not affect nitrogen balance. Starch is a glucose polymer, and the lack of starch will not affect nitrogen balance. Lysine is an essential amino acid, whereas serine can be synthesized from a derivative of glucose. Lack of lysine in the diet will lead to a negative nitrogen balance as existing protein is degraded to provide lysine for new protein synthesis.
A medical student has been studying for exams, and neglects to eat anything for 12 hours. At this point, the student opens a large bag of pretzels and eats every one of them in a short period. Which one of the following effects will this meal have on the student’s metabolic state?
(A) Liver glycogen stores will be replenished.
(B) The rate of gluconeogenesis will be
increased.
(C) The rate at which fatty acids are
converted to adipose triacylglycerols
will be reduced.
(D) Blood glucagon levels will increase.
(E) Glucose will be oxidized to lactate by
the brain and to CO2 and H2O by the red blood cells.
The answer is A. After a meal of carbohydrates (the major ingredient of pretzels), glycogen is stored in the liver and in muscle, and triacylglycerols are stored in adipose tissue. Owing to the rise in glucose level in the blood (from the carbohydrates in the pretzels), insulin is released from the pancreas and the level of glucagon in the blood decreases. Since blood glucose levels have increased, there is no longer a need for the liver to synthesize glucose, and gluconeogenesis decreases. The change in insulin-to-glucagon ratio also inhibits the breakdown of triacylglycerols and favors their synthesis. The brain oxidizes glucose to CO2 and H2O, whereas the red blood cells produce lactate from glucose, since red blood cells cannot carry out aerobic metabolism.
After a stressful week of exams, a medical student sleeps for 15 hours, then rests in bed for an hour before getting up for the day. Under these conditions, which one of the following statements concern- ing the student’s metabolic state would be correct?
(A) Liver glycogen stores are completely depleted.
(B) Liver gluconeogenesis has not yet been activated.
(C) Muscle glycogen stores are contributing to the maintenance of blood glucose levels.
(D) Fatty acids are being released from adipose triacylglycerol stores.
(E) The liver is producing and oxidizing ketone bodies to CO2 and H2O.
The answer is D. During fasting, fatty acids are released from adipose tissue and oxidized by other cells. Liver glycogen is not depleted until about 30 hours of fasting. After an overnight fast, both glycogenolysis and gluconeogenesis by the liver help maintain blood glucose levels. Muscle glycogen stores are not used to maintain blood glucose levels. The liver produces ketone bodies but does not oxidize them, but under the conditions described in this question, ketone body formation would be minimal.
A physician working in a refugee camp in Africa notices a fair number of children with emaciated arms and legs, yet a large protruding stomach and abdomen. An analysis of the children’s blood would show significantly reduced levels of which one of the following as compared with those in a healthy child? (A) Glucose (B) Ketone bodies (C) Albumin (D) Fatty acids (E) Glycogen
The answer is C. The children are exhibiting the effects of kwashiorkor, a disorder resulting from adequate calorie intake but insufficient calories from protein. This results in the liver producing less serum albumin (due to the lack of essential amino acids), which affects the osmotic balance of the blood and the fluid in the interstitial spaces. Owing to the reduction in osmotic pressure of the blood, water leaves the blood and enters the interstitial spaces, producing edema in the children (which leads to the expanded abdomen). The children are degrading muscle protein to allow the synthesis of new protein (due to a lack of essential amino acids), and this leads to the wasting of the arms and legs of children with this disorder. The children will exhibit normal or slightly elevated levels of ketone bodies and fatty acids in the blood, as the diet is calorie sufficient. Glycogen levels may only be slightly reduced (since the diet is calorie sufficient), but glycogen is not found in the blood. Glucose levels will be only slightly reduced, as gluconeogenesis will keep glucose levels near normal.
A 50-year-old male with a “pot belly” and a strong family history of heart attacks is going to his physician for advice on how to lose weight. He weighs 220 lb (100 kg) and is about 6’ tall (1.85 m). His lifestyle can be best described as sedentary.
What is this patient’s BMI? (A) 24 (B) 29 (C) 31 (D) 36 (E) 40
The answer is B. The BMI is equal to kg/m2, which in this case is equal to 100/1.852, which is about 29.
A 50-year-old male with a “pot belly” and a strong family history of heart attacks is going to his physician for advice on how to lose weight. He weighs 220 lb (100 kg) and is about 6’ tall (1.85 m). His lifestyle can be best described as sedentary.
Into which of the following categories does his BMI place him? (A) Underweight (B) Healthy (C) Overweight (preobese) (D) Obese (class I) (E) Obese (class II)
The answer is C. The patient is in the overweight (preobese) category with a BMI of 29. As indicated in Table 1.2, a BMI of ,18.5 is the underweight category, a BMI between 18.5 and 24.9 is the healthy range, a BMI between 25 and 30 is the overweight (preobese) category, and any BMI of 30 or above is considered the obese range. Class I obese is between 30 and 35, whereas class II obese is between 35 and 40. Class III obesity, or morbidly obese, is the classification for individuals with a BMI of 40 or higher.
A 50-year-old male with a “pot belly” and a strong family history of heart attacks is going to his physician for advice on how to lose weight. He weighs 220 lb (100 kg) and is about 6’ tall (1.85 m). His lifestyle can be best described as sedentary.
How many kilocalories per day would the patient need to maintain this weight? (A) 2,400 (B) 2,620 (C) 3,120 (D) 3,620 (E) 3,950
The answer is C. The DEE is equal to the BMR plus physical activity factor. For the patient in question, the BMR 5 24 kcal/kg/day 3 100 kg, or 2,400 kcal/day. Since the patient is sedentary, the activity level is 30% that of the BMR, or 720 kcal/day. The overall daily needs are therefore 2,400 1 720 kcal/day, or 3,120 kcal/day. If the patient consumes ,3,000 kcal/day, or increases his physical activity level, then weight loss would result.
