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with dietary excesses or deficiencies of minerals are described in subsequent chapters in conjunction

with their normal metabolic functions.

Which foods would provide Percy V. with good sources of folate and vitamin B12?Folate is found in fruits and vegetables: citrus fruits (e.g., oranges), green leafy vegetables

(e.g., spinach and broccoli), fortified cereals, and legumes (e.g., peas) (see Table 1.7).

Conversely, vitamin B12 is found only in foods of animal origin, including meats, eggs, and milk.

F. Water

Water constitutes one-half to four-fifths of the weight of the human body. The intake of water required per

day depends on the balance between the amount produced by body metabolism and the amount lost

through the skin, through expired air, and in the urine and feces. V. Dietary Guidelines

Dietary guidelines or goals are recommendations for food choices that can reduce the risk of developing

chronic diseases while maintaining an adequate intake of nutrients. Many studies have shown an

association between diet and physical activity and decreased risk of certain diseases, including

hypertension, atherosclerosis, stroke, diabetes, certain types of cancer, and osteoarthritis. Thus, the

American Heart Institute and the American Cancer Institute, as well as several other groups, have

developed diet and physical activity recommendations to decrease the risk of these diseases. The Dietary

Guidelines for Americans (2015–2020) are prepared by an advisory committee of researchers appointed

by the U.S. Department of Agriculture (USDA) and the U.S. Department of Health and Human Services to

review the current evidence and revise the guidelines accordingly every 5 years (you can view these at

the Web site listed in the references). Recommended servings of different food groups can be customized

for individuals accessing the USDA MyPlate Web site (see references). Physicians and dietitians can

tailor the dietary guidelines to meet the needs of their patients with specific medical conditions.

A. General Recommendations

Choose a healthy eating pattern at an appropriate calorie level to help achieve and maintain a

healthy body weight. For maintenance of weight, energy intake should balance energy expenditure.

Accumulate at least 30 minutes of moderate physical activity (such as walking at a pace of 3 to 4

miles per hour) daily and engage in muscle strengthening exercises at least 2 days per week. A

regular physical activity program helps in achieving and maintaining healthy weight, cardiovascular fitness, and strength.

Choose nutrient-dense foods in the amounts recommended by your personalized plan from MyPlate,

including a daily variety of whole grains, fruits, and vegetables; fat-free or low-fat dairy products;

and lean protein foods.

Practice food safety by frequently cleaning hands, cutting boards, and countertops; cooking foods to

safe temperatures; and refrigerating leftovers promptly. B. Carbohydrates

A diet rich in vegetables, fruits, and grain products should be chosen, providing 45% to 65% of itscalories as carbohydrates. A variety of vegetables from all of the subgroups (i.e., dark green, red

and orange, legumes, starchy, and other) and whole fruits should be included in a

healthy eating

pattern. In regard to grains (e.g., starches and other complex carbohydrates in the form of breads,

fortified cereals, rice, and pasta), at least half should be whole grains. In addition to energy,

vegetables, fruits, and grains supply vitamins, minerals, phytochemicals (protective compounds

such as carotenoids, flavonoids, and lycopene), and fiber. Fiber, the indigestible part of plant food,

has various beneficial effects, including relief of constipation.

The consumption of added sugars in foods and beverages should be limited to less than 10% of

total calories. Added sugars have no nutritional value other than calories, and they promote tooth

decay. C. Fats

Dietary fat should account for 20% to 35% of total calories, and saturated fatty acids should

account for <10% of total calories. Fats derived from fish, nuts, and vegetables, which are

primarily polyunsaturated and monosaturated fatty acids, are preferred. Owing to their saturated fat

content, meats such as fatty beef, lamb, pork, and poultry with skin and full-fat dairy products such

as cheese, whole milk, butter, and ice cream should be limited. Trans-fatty acids, such as the

partially hydrogenated vegetable oils found in stick margarines, baked goods, and fried foods,

should be avoided.

Although saturated and trans fats have a greater impact than dietary cholesterol on lowering lowdensity lipoprotein cholesterol, many organizations recommend that cholesterol intake be <300

mg/day in persons without atherosclerotic disease and <200 mg/day in those with established

atherosclerosis. Major sources of dietary cholesterol in the American diet include beef, poultry,

processed meats, eggs, cheese, and ice cream.

Cholesterol is obtained from the diet and is synthesized in most cells of the body. It is a

component of cell membranes and the precursor of steroid hormones and of the bile salts

used for fat absorption. High concentrations of cholesterol in the blood, particularly the

cholesterol in lipoprotein particles called low-density lipoproteins (LDL), contribute to the

formation of atherosclerotic plaques inside the lumen of arterial vessels, particularly in the heart

and brain. These plaques (fatty deposits on arterial walls) can obstruct blood flow to these vital

organs, causing heart attacks and strokes. A high content of saturated fat and trans fat in the diet

tends to increase circulatory levels of LDL cholesterol and contributes to the development of

atherosclerosis. D. Proteins

Protein intake for adults should be approximately 0.8 g/kg healthy body weight per day. The protein

should be of high quality and should be obtained from sources low in saturated fat (e.g., fish,

poultry, beans, lentils, low-fat/fat-free dairy products, soy products). Vegans should eat a mixtureof plant proteins that ensures the intake of adequate amounts of the essential amino acids.

E. Alcohol

Alcohol consumption should not exceed moderate drinking and should only be consumed by adults

of legal drinking age. Moderation is defined as no more than one drink per day for women and no

more than two drinks per day for men. A drink is defined as 12 oz of beer, 5 oz of wine (a little

over 0.5 cup), or 1.5 oz of an 80-proof liquor such as whiskey. Pregnant women should drink no

alcohol. The ingestion of alcohol by pregnant women can result in fetal alcohol syndrome (FAS),

which is marked by prenatal and postnatal growth deficiency; developmental delay; and

craniofacial, limb, and cardiovascular defects. F. Vitamins and Minerals

Sodium intake should be decreased in most individuals. Sodium is usually consumed as salt, NaCl.

Less than 2.3 g of sodium should be consumed daily, which is equivalent to the sodium in 1 tbsp of

salt.

Many of the required vitamins and minerals can be obtained from eating a variety of fruits,

vegetables, and grains (particularly whole grains). Low-fat or fat-free dairy products are an

excellent source of calcium; some dark green leafy vegetables provide available calcium. Lean

meats, shellfish, poultry, dark meat, cooked dry beans, and some leafy green vegetables provide

good sources of iron. Vitamin B12 is found only in animal sources.

Dietary supplementation in excess of the recommended amounts (e.g., megavitamin regimens)

should be avoided.

Fluoride should be present in the diet, at least during the years of tooth formation, as a protection

against dental caries.

The high content of sodium (in table salt) in the average American diet appears to be related

to the development of hypertension (high blood pressure) in individuals who are genetically

predisposed to this disorder. VI. Xenobiotics

In addition to nutrients, our diet also contains a large number of chemicals called xenobiotics, which have

no nutritional value, are of no use in the body, and can be harmful if consumed in excessive amounts.

These compounds occur naturally in foods, can enter the food chain as contaminants, or can be

deliberately introduced as food additives.

Dietary guidelines of the American Cancer Society and the American Institute for Cancer Research

make recommendations relevant to the ingestion of xenobiotic compounds, particularly carcinogens. The

dietary advice that we eat a variety of food helps to protect us against the ingestion of a toxic level of any

one xenobiotic compound. It is also suggested that we reduce consumption of salt-cured, smoked, and

charred foods, which contain chemicals that can contribute to the development of cancer. Other guidelinesencourage the ingestion of fruits and vegetables that contain protective phytochemicals that act as

antioxidants. CLINICAL COM M ENTS

Otto S. Otto S. sought help in reducing his weight of 187 lb (BMI of 27) to his previous level of

154 lb (BMI of 22, in the middle of the healthy range). Otto S. is 5 ft 10 in tall, and he calculated

that his maximum healthy weight was 173 lb. He planned on becoming a family physician, and he knew

that he would be better able to counsel patients in healthy lifestyle behaviors such

as diet and physical

activity if he practiced them himself. With this information and assurances from the physician that he was

otherwise in good health, Otto embarked on a weight loss program. One of his strategies involved

recording all the food he ate and the portions. To analyze his diet for calories, saturated fat, and nutrients,

he used the MyPlate personalized Plan (see references), available online from the USDA Center for

Nutrition Policy and Promotion (CNPP). As part of his program, Otto met with a registered dietitian who

provided the following: tips for buying and cooking nutrient-dense foods at a reasonable cost, tips for

modifying eating behavior (e.g., slowing down the pace of eating), the setting of realistic achievable goals

(e.g., loss of 10% of initial body weight within 6 months), and tips for dealing with relapse into prior

habits.

Ivan A. Ivan A. weighed 264 lb and was 70 in tall with a heavy skeletal frame. For a male of this

height, a BMI of 18.5 to 24.9 would correspond to a weight between 129 lb and 173 lb. He is

currently almost 100 lb overweight, and his BMI of 37.9 is in the obese range. Mr. A.’s physician cautioned him that exogenous obesity (caused by overeating) represents a risk

factor for atherosclerotic cardiovascular disease, particularly when the distribution of fat is primarily

“central” or in the abdominal region (apple shape, in contrast to the pear shape, in which adipose tissue is

deposited in the buttocks and hips). In addition, obesity may lead to other cardiovascular risk factors such

as hypertension (high blood pressure), hyperlipidemia (high blood lipid levels), and type 2 diabetes

mellitus (characterized by hyperglycemia). Mr. A. already has elevated blood pressure. Furthermore, his

total serum cholesterol level was 296 mg/dL, well above the desired normal value (200 mg/dL).

Mr. A. was referred to the hospital’s weight reduction center, where a team of physicians, dietitians,

and psychologists could assist him in reaching a healthy BMI.

The prevalence of obesity in the US population is increasing. In 1962, 12.8% of the population had a BMI ≥30 and therefore were clinically obese. That number increased to

14.5% by 1980 and to 22.5% by 1998. An additional 30% were overweight in 1998 (BMI = 25.0

to 29.9). In 2012, based on BMI values, 35.1% of adults were classified as obese, and an

additional 33.9% were classified as overweight. It is apparent, therefore, that more than twothirds of the population is currently overweight or obese.

An elevated BMI increases cardiovascular risk factors, including hypertension, diabetes

mellitus, and alterations in blood lipid levels. It also increases the risk for respiratory problems,

gallbladder disease, and certain types of cancer.When Mr. A. met with the dietitian to discuss his weight loss plans, he received the

following advice: tips for devising a meal plan that provides consistent amounts of complex

carbohydrates throughout the day for glucose control while limiting calories, saturated and trans

fat, and sodium and tips for small, incremental dietary changes to achieve a diet that is lower in

trans fat, sodium, and refined carbohydrates while high in essential nutrients via whole grains,

fruits, vegetables, lean protein, and nonfat/low-fat dairy products. Mr. A. was also counseled in a

manner similar to Otto S., with an emphasis on the importance of losing 10% of initial body

weight for improvement in blood pressure, blood lipids, and glucose control. Ann R. Because of her history and physical examination, Ann R. was diagnosed as having early

anorexia nervosa, a psychiatric illness involving a disturbance in body image, which results in low

body weight, malnutrition, and other medical complications. Miss R. was referred to a multidisciplinary

team that included a psychiatrist with expertise in anorexia nervosa, and a program of psychotherapy and

behavior modification was initiated.

Percy V. Percy V. weighed 125 lb and was 71 in tall (without shoes) with a medium frame. His

BMI was 17.5, which is significantly underweight. At the time his wife died, he weighed 147 lb.

For his height, a BMI in the healthy weight range corresponds to weights between 132 lb and 178 lb.

Mr. V.’s malnourished state was reflected in his admission laboratory profile. The results of

hematologic studies were consistent with an iron deficiency anemia complicated by low levels of folic

acid and vitamin B12, two vitamins that can affect the development of normal red blood cells. His low

serum albumin level was caused by insufficient protein intake and a shortage of essential amino acids,

which result in a reduced ability to synthesize body proteins. The psychiatrist requested a consultation

with a hospital dietitian to evaluate the extent of Mr. V.’s severe acute malnutrition caused by inadequate

intake of protein, energy, vitamins, and minerals. BIOCHEMICAL COMMENTS

Dietary Reference Intakes. DRIs are quantitative estimates of nutrient intakes that can be used in

evaluating and planning diets for healthy people. They are prepared by the Standing Committee on

the Scientific Evaluation of Dietary Reference Intakes (DRI) of the Food and Nutrition Board, Institute of

Medicine, and the National Academy of Science, with active input of Health Canada. The four reference

intake values are the RDA, the Estimated Average Requirement (EAR), the AI, and the UL. Practitioners

use the RDA, AI, and ULvalues for evaluating patients’ nutrient intakes. Researchers and policymakers

use the EAR values as an estimate of nutrient intakes of populations rather than individuals. For each

nutrient, the Committee has reviewed available literature on studies with humans and established criteria

for adequate intake, such as prevention of certain deficiency symptoms, prevention of developmental

abnormalities, or decreased risk of chronic degenerative disease. The criteria are not always the same for

each life stage group. A requirement is defined as the lowest continuing intake level of a nutrient able to

satisfy these criteria. The EAR is the daily intake value that is estimated to meet the requirement in half of

the apparently healthy individuals in a life stage or gender group. The RDA is the EAR plus 2 standarddeviations of the mean, which is the amount that should satisfy the requirement in 97% to 98% of the

population. The AI level instead of an RDA is set for nutrients when there is not enough data to determine

the EAR.

The UL refers to the highest level of daily nutrient intake consumed over time that is likely to pose no

risks of adverse effects for almost all healthy individuals in the general

population. Adverse effects are

defined as any significant alteration in the structure or function of the human organism. The UL does not

mean that most individuals who consume more than the UL will suffer adverse health effects but that the

risk of adverse effects increases as intake increases above the UL. KEY CONCEPTS

Fuel is provided in the form of carbohydrates, fats, and proteins in our diet. Energy is obtained from the fuel by oxidizing it to carbon dioxide and water. Unused fuel can be stored as triacylglycerol (fat) or glycogen (carbohydrate) within the body.

Weight gain or loss is a balance between the energy consumed in our diet and the energy required

each day to drive the basic functions of our body and our physical activity. The daily energy

expenditure (DEE) is the amount of fuel consumed in a 24-hour period.

The basal metabolic rate (BMR) is a measure of the energy required to maintain involuntary bodily

functions such as respiration, contraction of the heart muscle, biosynthetic processes, and

establishment of ion gradients across neuronal membranes.

The DEE is determined by the BMR and the individual’s activity level while awake. The body mass index (BMI) is a ratio of weight to height that is used to determine a healthy weight

for an individual and to classify a person as underweight, healthy weight, overweight, or obese.

In addition to macronutrients, the diet provides vitamins, minerals, essential fatty acids, and

essential amino acids.

The Recommended Dietary Allowance (RDA) and the Adequate Intake (AI) provide quantitative

estimates of nutrient requirements.

The Tolerable Upper Intake Level (UL) indicates the highest level of daily nutrient uptake that is

likely to pose no risk of adverse effects.

A summary of the diseases/disorders discussed in this chapter are presented in Table 1.9.REVIEW QUESTIONS—CHAPTER 1

Directions: For each question below, select the single best answer.

1.A dietitian is counseling a patient with celiac sprue (intolerance to gluten, leading to malabsorption

issues in the intestine) and describing a diet with appropriate carbohydrate, fat, and protein content.

Once properly absorbed, the major fate of these compounds during respiration is which ONE of the

following?

A. They are stored as triacylglycerols. B. They are oxidized to generate ATP.

C. They release energy principally as heat.

D. They combine with CO2 and H2O and are stored.

E. They combine with other dietary components in anabolic pathways.

2.A dietitian is counseling a patient with celiac sprue (intolerance to gluten, leading to malabsorption

issues in the intestine) who has experienced steatorrhea (fatty stools caused by poor absorption of

dietary lipids in the intestine) for a number of years. The dietitian, in addition to describing

appropriate carbohydrates, lipids, and proteins that will not trigger the malabsorption issue, also

encourages the patient to take certain vitamins. Which ONE of the following vitamins is most likely

on this list? A. Vitamin C B. Folic acid C. Vitamin B12 D. Vitamin K

E. Vitamin B1

3.Mrs. Jones is a sedentary 83-year-old woman who is 5 ft 4 in tall and weighs 125 lb. She has been atthis weight for about a year. She says that a typical diet for her includes a breakfast of toast (white

bread, no butter), a boiled egg, and coffee with cream. For lunch she often has a cheese sandwich

(white bread) and a glass of whole milk. For supper she prefers cream of chicken soup and a slice of

frosted cake. Mrs. Jones’s diet is most likely to be inadequate in which one of the following?

A. Vitamin C B. Protein C. Calcium

D. Vitamin B12 E. Calories

4.A patient is trying to lose weight and wonders what her ideal number of calories per day might be. A

dietitian is helping her by estimating the BMR, the DIT, and physical activity. The BMR is best

estimated by consideration of which one of the following?

A. It is equivalent to the caloric requirement of our major organs and resting muscle.

B. It is generally higher per kilogram of body weight in women than in men. C. It is generally lower per kilogram of body weight in children than adults. D. It is decreased in a cold environment.

E. It is approximately equivalent to the DEE.

5.A friend of yours has decided to go on a crash diet, consuming only 700 calories per day. You advise

your friend that he is at risk for certain dietary deficiencies and inform him of the RDA, which is

best described by which one of the following?

A. The average amount of a nutrient required each day to maintain normal function in 50% of the US

population

B. The average amount of a nutrient ingested daily by 50% of the US population

C. The minimum amount of a nutrient ingested daily that prevents deficiency symptoms D. A reasonable dietary goal for the intake of a nutrient by a healthy individual E. It is based principally on data obtained with laboratory animals.

6.A 35-year-old sedentary male patient weighing 120 kg was experiencing angina (chest pain) and

other signs of coronary artery disease. His physician, in consultation with a registered dietitian,

conducted a 3-day dietary recall. The patient consumed an average of 585 g of carbohydrate, 150 g

of protein, and 95 g of fat each day. In addition, he drank 45 g of alcohol. The patient’s diet is best

described by which one of the following?

A. He consumed between 2,500 and 3,000 kcal/day.

B. He had a fat intake within the range recommended in current dietary guidelines (i.e., year 2010).

C. He consumed 50% of his calories as alcohol. D. He was deficient in protein intake.

E. He was in negative caloric balance.

7.A sedentary 75-kg male is trying to lose weight and has begun a

calorie-restricted diet. He has

reduced his daily intake by 10 g of carbohydrates, 10 g of fat, 10 g of protein, and 10 g of ethanol. By

what percentage has this man reduced his daily intake as compared to what he would require to

maintain his current weight? A. 5%B. 10%

C.15%

D.20%

E.25%

8. A 45-year old man developed deep vein thrombosis and subsequently a pulmonary

embolism. After

recovery, the patient was placed on warfarin to prevent future blood clots. The patient was

counseled by a dietitian to limit his consumption of which one of the following foods because of the

finding that eating the food could interfere with the action of warfarin?

A.Egg yolks

B.Yellow vegetables

C.Citrus fruits

D.Green leafy vegetables

E.Skinless chicken

9.A 25-year-old female with Hashimoto’s thyroiditis is being treated with thyroid hormone

replacement and is now euthyroid. She wishes to lose some of the weight she gained while she was

in a hypothyroid state. In order to help her lose weight, her dietitian must determine her daily energy

expenditure in order to determine a diet with fewer calories than her DEE. The patient weighs 70 kg,

is moderately active (1 to 2 hours of exercise 5 days per week), and is currently consuming 2,700

calories per day. If the patient is to lose 1 lb per week, she would need to reduce her daily

consumption by how many calories per day? A. 200

B. 400 C. 600 D. 800 E. 1,000

10.A patient with cirrhosis is having mental status changes owing to elevated ammonia levels in his

blood. In prescribing a diet to reduce ammonia production in this patient, which class of nutrients

should be most restricted? A. Ethanol

B. Lipids C. Proteins

D. Carbohydrates

E. Water-soluble vitamins ANSWERS TO REVIEW QUESTIONS

1.The answer is B. In the process of respiration, O2 is consumed and fuels are oxidized to CO2 and

H2O. The energy from the oxidation reactions is used to generate ATP from ADP and Pi. However,

a small amount of energy is also released as heat (thus, C is incorrect). Although fuels can be

stored as triacylglycerols, this is not part of respiration (thus, A is incorrect). Respiration is a

catabolic pathway (fuels are degraded), as opposed to an anabolic pathway (compounds combineto make larger molecules) (thus, E is incorrect).

2.The answer is D. Vitamin K is a fat-soluble vitamin, and it is absorbed from the small intestine in

the presence of lipids. If lipids cannot be absorbed, the fat-soluble vitamins (vitamins A, D, E,

and K) also will not be absorbed. The other vitamins listed (vitamins B1, C, folic acid, B12) are

all water-soluble vitamins that do not require the presence of lipid for absorption from the

intestinal lumen.

3.The answer is A. Mrs. Jones’s diet lacks fruits and vegetables, both of which are good sources of

vitamin C. Her diet is adequate in protein, as eggs, milk, cheese and cream contain significant

levels of protein. Her calcium levels should be fine owing to the milk, cream, and cheese in her

diet. Vitamin B12 is derived from foods of animal origin, such as eggs, milk, and cheese. As the

patient’s weight has been stable for a year, her diet contains sufficient calories to allow her to

maintain this weight, which is in the normal range for a patient who is 5 ft 4 in tall, as her BMI is

21.5.

4.The answer is A. The BMR is the calories being expended by a recently awakened resting person

who has fasted 12 to 18 hours and is at 20°C. It is equivalent to the energy expenditure of our

major organs and resting skeletal muscle. Women generally have a lower BMR per kilogram of

body weight because more of their body weight is usually metabolically less-active adipose

tissue. Children have a higher BMR per kilogram of body weight because more of their body

weight is metabolically active organs like the brain. The BMR increases in a cold environment

because more energy is being expended to generate heat. The BMR is not equivalent to our DEE,

which includes BMR, physical activity, and DIT.

5.The answer is D. The RDA of a nutrient is determined from the EAR plus 2 standard deviations

of the mean (SD) and should meet the needs for 97% to 98% of the healthy population. It is

therefore a reasonable goal for the intake of a healthy individual. The EAR is the amount that

prevents development of established signs of deficiency in 50% of the healthy population.

Although data with laboratory animals have been used to establish deficiency symptoms, RDAs

are based on data collected on nutrient ingestion by humans.

6.The answer is B. The recommended total fat intake is <30% of total calories. His total caloric

consumption was 4,110 calories/day (carbohydrate, 4 × 585 = 2,340 calories; protein

150× 4 =

600calories; fat, 95 × 9 = 855 calories; alcohol, 45 × 7 = 315 calories) (thus, A is incorrect). His

fat intake was 21% (855 ÷ 4,110) of his total caloric intake. His alcohol intake was 7.7% (315 ÷

4,110) (thus, C is incorrect). His protein intake was well above the RDA of 0.8 g/kg body weight

(thus, D is incorrect). His BMR is roughly 24 calories/day/kg body weight, or 2,880 calories/day

(it will actually be less because he is obese and has a greater proportion of metabolically lessactive tissue than the average 70-kg man). His DEE is about 3,744 calories/day (1.3 × 2,880) or

less. Thus, his intake is greater than his expenditure, and he is in positive caloric balance and is

gaining weight (thus, E is incorrect).

7.The answer is B. The man weighs 75 kg, so a rough estimate of his daily caloric need (to

maintain his weight) is 75 × 24 × 1.3 = 2,340 calories/day (1.3 is the sedentary activity factor).

The man has reduced his daily intake by 240 calories (10 g of carbohydrates is 40 calories; 10 g

of protein is 40 calories; 10 g of lipid is 90 calories; 10 g of ethanol is 70 calories; 40 + 40 + 90+ 70 = 240). Thus, the man has reduced his daily intake by approximately 10% of that needed to

maintain his weight (240/2,340).

8.The answer is D. Warfarin acts by inhibiting the ability of vitamin K to participate in reactions

required by clotting factors. If one’s diet contains additional vitamin K, the efficacy of the

warfarin could be reduced. Green leafy vegetables are an excellent source of vitamin K, and their

consumption should be limited while on warfarin therapy.

9.The answer is D. The patient’s DEE is calculated as 70 × 21.6 × 1.6 = 2,420 (70 kg weight, times

21.6 kcal/kg/day, times 1.6 activity factor for being moderately active). Because the patient is

currently consuming 2,700 calories/day, she is gaining weight despite her activity. To lose 1 lb of

weight, a loss of 3,500 calories must occur. Over a 1-week period, that is 500 calories/day. Thus,

the patient should be consuming 1,920 calories/day to lose 1 lb per week, which is approximately

800fewer calories/day based on her current consumption.

10.The answer is C. Ethanol, lipids (triglycerides), and carbohydrates do not contain a nitrogen

group that is converted to ammonia during its catabolism—only proteins do. Water-soluble

vitamins are present at low levels and are not appreciably catabolized, so their contribution to

ammonia production is low as compared to protein catabolism.2 The Fed or Absorptive State

For additional ancillary materials related to this chapter, please visit thePoint. The Fed State. During a meal, we ingest carbohydrates, lipids, and proteins, which are subsequently

digested and absorbed. Some of this food is oxidized to meet the immediate energy needs of the body.

The amount consumed in excess of the body’s energy needs is transported to the fuel depots, where it is

stored. During the period from the start of absorption until absorption is completed, we are in the fed, or

absorptive, state. Whether a fuel is oxidized or stored in the fed state is determined principally by the

concentration of two endocrine hormones in the blood, insulin and glucagon.

Fate of Carbohydrates. Dietary carbohydrates are digested to monosaccharides, which are absorbed

into the blood. The major monosaccharide in the blood is glucose (Fig. 2.1). After a meal, glucose is

oxidized by various tissues for energy, enters biosynthetic pathways, and is stored as glycogen, mainly in

liver and muscle. Glucose is the major biosynthetic precursor in the body, and the carbon skeletons of

most of the compounds we synthesize can be synthesized from glucose. Glucose is also converted to

triacylglycerols. The liver packages triacylglycerols, made from glucose or from fatty acids obtained

from the blood, into very low-density lipoproteins (VLDL) and releases them into the blood. The fatty

acids of the VLDLare stored mainly as triacylglycerols in adipose tissue, but some may be used to meet

the energy needs of cells.Fate of Proteins. Dietary proteins are digested to amino acids, which are absorbed into the blood. In

cells, the amino acids are converted to proteins or used to make various nitrogen-containing compounds

such as neurotransmitters and heme. The carbon skeleton may also be oxidized for energy directly or

converted to glucose.

Fate of Fats. Triacylglycerols are the major lipids in the diet. They are digested to fatty acids and 2-

monoacylglycerols, which are resynthesized into triacylglycerols in intestinal epithelial cells, packaged

in chylomicrons, and secreted by way of the lymph into the blood. The fatty acids of the chylomicron

triacylglycerols are stored mainly as triacylglycerols in adipose cells. They are subsequently oxidized for