1Elsevier items and derived items © 2007 by Saunders, an imprint of Elsevier, Inc. Chapter 9 Nutrition.

1Elsevier items and derived items © 2007 by Saunders, an imprint of Elsevier, Inc.

Chapter 9

Nutrition


Learning Objectives• Explain the role of the gastrointestinal system in the digestion of

food.• Describe how food is digested and absorbed.• List the functions of each of the six classes of essential nutrients.• Define macronutrient and micronutrient.• Identify the food sources of proteins, carbohydrates, and fats.• Identify the food sources of dietary fiber.• List the possible health benefits of dietary fiber.• Identify the food sources of each of the vitamins and minerals.• Describe the changes in nutrient needs as an individual ages.• Differentiate between anorexia nervosa, bulimia, and binge eating

disorder.• Discuss the different types of nutritional support.• Identify guidelines for the nutritional assessment.


Anatomy and Physiology of the Gastrointestinal System


Gastrointestinal System (GI tract or “gut”)

• The long, continuous tube that receives and transports food, absorbs nutrients, and eliminates waste products of digestion

• Primary organs • Mouth, pharynx, esophagus, stomach, small intestine, and

large intestine

• Accessory organs • Liver, gallbladder, and pancreas

• Roles in food digestion even though not part of digestive tract


Digestion and Absorption

• 92% to 97% of diet digested and absorbed• Water, simple sugars, vitamins, minerals, and

alcohol absorbed in their original form• Lipids, proteins, and complex sugars must be

converted to simple forms before they are absorbed


Digestion and Absorption

• Hydrolysis• Water splits complex molecules into smaller units

• Enzymes • Govern the process of hydrolysis, along with bile and

hydrochloric acid• Help break down food particles to their simplest form so

nutrients can be absorbed • Found throughout intestinal tract, except in the large intestine

• Only water, salt, vitamins, and minerals are absorbed in the colon


Regulators of the Gastrointestinal Tract

• Neural control• Managed by autonomic nervous system and nerve

network in gut wall called the enteric nervous system

• Autonomic system: sympathetic and parasympathetic nerves

• Parasympathetic nerves stimulate digestive activity

• Sympathetic nerves inhibit activity

• Parasympathetic effect conveyed by vagus nerve: acid stimulation in stomach in response to sight/smell of food

• Enteric nervous system receives information from receptors in gastric mucosa that are sensitive to acidity of the gastrointestinal tract and the feeling of fullness


Regulators of the Gastrointestinal Tract

• Hormone secretion• Secreted into the gastrointestinal tract to help

regulate gastric pH, gastric motility, and appetite • Stimulate the pancreas to secrete insulin and

enzymes


Digestive Process: Mouth

• Teeth grind and crush food into small particles • Food forms mass moistened and lubricated by

saliva • A secretion containing an enzyme known as

amylase (ptyalin) digests any present starch • Mass, or bolus, then passed to the pharynx

and through the esophagus by the process of swallowing

• Peristalsis moves the food rapidly through the esophagus into the stomach


Digestive Process: Stomach

• The mass is mixed with gastric secretions • Active chemical digestion is accomplished by the

secretion of gastric juice • Produces average of 2000 to 2500 ml gastric juice

daily • The juice contains hydrochloric acid, enzymes,

mucus, and the GI hormone gastrin • Aids in digestion by converting the mass to a

semiliquid substance called chyme


Digestive Process: Stomach

• Normally emptied in 1 to 4 hours• Carbohydrates leave the stomach most rapidly,

followed by protein, and then fat • Valves (sphincters) at entrance (cardiac

sphincter) and exit (pyloric sphincter) of the stomach prevent backflow of food from stomach into pharynx and from duodenum into the stomach


Digestive Process: Small Intestine

• Divided into the duodenum, the jejunum, and the ileum

• Most digestion completed in duodenum; jejunum and ileum function mostly in the absorption of nutrients

• The remaining chyme is delivered to the large intestine


Digestive Process: Large Intestine

• Water and electrolytes are absorbed, leaving a mass of wastes called feces

• Fecal mass is stored in the rectum, where it triggers the defecation reflex

• When anal sphincters relax, feces pass out of the body through the anus


Mechanisms of Absorption

• Absorption is accomplished by the combination of the processes of diffusion and active transport • Diffusion

• Movement of particles from an area of higher concentration to an area of lower concentration

• Active transport• Requires the input of energy for the movement of particles

across a membrane against an energy gradient• Requires a carrier protein• Best-known carrier is the intrinsic factor, which is

responsible for the absorption of vitamin B12


Mechanisms of Absorption

• Small intestine• Primary organ of absorption • 22 feet long and arranged in folds• Surface of folds covered with fingerlike projections

called villi• Absorb nutrients into the blood and lymph vessels that

support them

• Absorbs several hundred grams of carbohydrate, 100 g or more of fat, 50 to 100 g amino acids, 50 to 100 g of ions, and 7 to 8 L of water each day


Nutrients: Carbohydrates

• Digestion begins in the mouth, where the enzyme amylase is released• In the stomach, amylase activity halted when it

comes into contact with hydrochloric acid • If carbohydrates remain in the stomach long

enough, hydrochloric acid reduces most to their simplest form

• Stomach generally empties into the small intestine before this occurs, so most of the digestion of carbohydrates occurs within the small intestine


Nutrients: Carbohydrates

• In the small intestine, pancreatic amylase is released to continue carbohydrate digestion

• Pass through the villi into the bloodstream, where carbohydrates carried by the portal vein to the liver

• From the liver, most of the glucose is transported to the tissues

• Some stored for later use in the liver in the form of glycogen and in the muscle

• Some forms, particularly fiber, cannot be digested by humans and are excreted unchanged in the feces


Nutrients: Protein

• Digestion does not begin until it reaches the stomach• Split into smaller molecules • Most digestion occurs in the duodenum• Almost all of the protein is absorbed by the time it

reaches the end of the jejunum • Only 1% of ingested protein found in the feces


Nutrients: Fat

• Digestion begins in the stomach • Gastric lipase

• An enzyme, breaks down the triglycerides that make up fat into fatty acids and glycerol

• Major portion of fat digestion takes place in the small intestine

• Peristaltic action of small intestine, along with bile secreted by the liver, breaks down the larger fat globules into smaller particles


Nutrients: Fluids, Vitamins, and Minerals

• Absorbed through the intestinal mucosa • Each day about 8 L of fluid from the body pass

back and forth across gut membrane to keep the nutrients in solution

• Vitamins and water pass unchanged from the small intestine into the blood by passive diffusion

• Mineral absorption is a more active, complex process that takes place in several stages


Factors Affecting Digestion

• Psychological state• Look, smell, and taste of food have effect on digestion• Emotions such as fear, anger, and worry can inhibit peristalsis

and depress gastric secretions

• Bacterial action• Needed to help form vitamin K, vitamin B12, thiamine, and

riboflavin• Produce various gases, acids, and other toxic substances

• Food processing• Cooked foods generally more digestible than raw foods


Energy Expenditure

• Measurement of energy expenditure• Basal metabolic rate (BMR)

• Factors that can cause the metabolic rate to vary• Body size and composition

• Periods of growth

• Secretion of hormones

• Temperature

• Menstrual cycle

• Pregnancy


Energy Expenditure

• Energy measurements and calculations• Calorie

• Standard unit for measuring energy• Amount of heat energy needed to increase temperature of 1 g

of water at standard temperature by 1° C

• Measure of human energy expenditure• Direct calorimetry• Indirect calorimetry• Doubly labeled water


Carbohydrates

• Organic compounds consisting of carbon, hydrogen, and oxygen

• All the sugars and starches that people eat and most types of fibers

• Plants manufacture and store carbohydrates as their chief source of energy

• Glucose main sugar in the blood and body’s basic fuel; serves as primary source of energy


Carbohydrates

• Classified according to the number of simple sugars or saccharides• Monosaccharides

• 1 saccharide

• Disaccharides• 2 saccharides

• Oligosaccharides• 3 to 10 monosaccharides

• Polysaccharides• 10 to 10,000 or more molecules


Carbohydrates

• Metabolism• Converted to glucose for immediate use by the body’s

cells and to glycogen for storage • Serum glucose level maintained at normal through the

regular intake of nutrients, storage or breakdown of glycogen, glucogenesis, and gluconeogenesis

• Normal blood glucose levels: 70 to 100 mg/100 ml under fasting conditions

• After a meal, blood glucose level may rise to

130 mg/100 ml but returns to normal within 2 to 3 hours


Carbohydrates

• Dietary fiber• A group of polysaccharides that act differently from

other carbohydrates • Found only in plant foods and are resistant to

human digestive enzymes • Major digestive role is to help form a soft, firm stool

and to aid in the process of elimination• Types

• Insoluble• Soluble


Carbohydrates

• Functions of carbohydrates• Major source of energy to body tissues• Sole source of energy for the brain• Maintain functional integrity of nerve tissue• Spare fats from being used for metabolism • Precursors (basic building blocks) for other

physiologic substances

• Recommended Dietary Allowance• Carbohydrates should comprise 45% to 65%


Lipids

• Include fats, oils, waxes, and related compounds

• May be solid or liquid forms • Insoluble in water• Contain carbon, hydrogen, and oxygen• Triglycerides: most common fat found in foods

of both animal and plant origin


Lipids

• Saturated fatty acids• Loaded with all the hydrogen atoms they can carry• Solid at room temperature

• Unsaturated fatty acids • Do not have all the hydrogen atoms they can carry• Liquid at room temperature


Lipid Transport and Storage

• Most are absorbed into the lymphatic system through the intestinal mucosa • The exception is certain fatty acids that are

absorbed directly into the portal blood

• For fat to be digested, it must be emulsified, or pulled into suspension with digestive juices • Bile (secretion of liver) needed to emulsify fat


Lipid Transport and Storage

• Once emulsified, fats can be broken down and absorbed

• Lipoproteins• Protein that transports lipids in the bloodstream• Chylomicrons, high-density lipoproteins (HDLs),

low-density lipoproteins (LDLs), and very-low-density lipoproteins (VLDLs)


Lipid Metabolism

• A source of energy for most body tissues except the brain, blood cells, skin, and renal medulla

• Lipolysis • Fat cells release glycerol and free fatty acids

• Liver converts it to triglycerides or glucose• Free fatty acids bind to albumin for transportation in the

blood and interstitial tissue • Most lipids carried to liver for conversion to energy or

for the synthesis of new triglycerides


Recommended Dietary Allowance

• 20% to 35% of the adult diet should be composed of fats

• Unsaturated fats rather than saturated fats minimize the risk of heart disease


Food Sources of Fat

• Saturated fats• Animal products: beef, dairy products, and eggs

• Unsaturated fats• Vegetable oils, including corn oil, cottonseed oil,

and safflower oil


Lipid Function

• Store energy• Maintain healthy skin and hair• Carry fat-soluble vitamins• Supply essential fatty acids• Promote satiety


Proteins

• Basic structure of a chain of amino acids that can form many different configurations and combine with other substances

• Contains carbon, hydrogen, oxygen, nitrogen, sulfur: sometimes metals, acids, lipids, polysaccharides

• Simple proteins• Made of only amino acids

• Conjugated proteins • Made of amino acids in combination with other

substances


Proteins

• Amino acids• Nine essential: must be obtained from the diet • Body can manufacture enough of the other amino

acids from the essential amino acids• Complete protein

• Contains all 9 essential amino acids in sufficient quantity and ratio for the body’s needs

• Incomplete proteins• Lack one or more of the essential amino acids


Protein Metabolism and Synthesis

• Deamination • Protein is broken down in the small intestine to the

constituent amino acids

• Protein synthesis • Controlled by DNA in the cells • DNA: provides the form to link up the exact

combination of amino acids needed to form a particular protein


Protein Deficiency

• The body cannot store protein, so it needs to be eaten each day

• If protein intake is inadequate, nitrogen will be conserved by the kidneys, causing the urine nitrogen to be low


Evaluation of Protein Quality

• Should include both the quantity and the quality of the protein consumed

• Eating a mixture of foods in a meal, if the quantity is sufficient, tends to provide all of the essential amino acids


Functions of Proteins

• Furnish building blocks (amino acids) to build and repair tissue

• Serve as an energy source• Help form enzymes, hormones, and other body

fluids and secretions• Assist in the transport of fats, fat-soluble

vitamins, and other substances• Help maintain osmolarity of body fluids


Recommended Dietary Allowance

• Should contribute 10% to 35% of the macronutrients in the adult diet


Vitamins

• Fat soluble • Vitamins A, D, E, and K• Usually absorbed in the body with other lipids

• Water soluble• B-complex group (thiamine, riboflavin, niacin, B6,

folate, B12, pantothenic acid, and biotin) and vitamin C (ascorbic acid)

• Readily excreted from the body


Minerals

• Enzyme regulation, maintain acid-base balance and osmotic pressure, and maintain nerve and muscular irritability

• Macrominerals• Calcium, phosphorus, magnesium, sulfur, sodium,

chloride, potassium

• Microminerals or trace elements• Iron, zinc, iodine


Minerals

• Ultratrace elements• Selenium, chromium, copper, manganese,

molybdenum, boron, cobalt

• Ionized forms• Sodium, potassium

• Constituents of organic compounds• Phospholipids, hemoglobin


Water

• Largest component of the body and tissues; essential to all body life processes

• Intake of water is controlled by thirst• Also ingested through food• The body cannot store water

• Essential that all living things replenish water daily to maintain health and efficiency


Water

• The longest that people can live without water is approximately 4 days

• Adults generally should take in about 2500 ml, or 2 to 3 quarts, per day


Age-Related Changes

• Energy• Normal decline in metabolism and common

decrease in physical activity, lower energy needs with age

• Often reduce the kilocalories taken in per day • Can result in inadequate intake of essential nutrients

• Psychosocial factors also may lead to poor nutrition in the older person

• Depression, cognitive impairment, and loneliness


Nutritional Care of the Older Adult

• Dietary planning• Meals need to be appealing, taking into

consideration individual likes and dislikes, and should be tasteful and filling

• Nutrition programs • Community-based programs, administered by public

and private agencies, provide hot, nutritious meals to older adults


Nutritional Care of the Older Adult

• Nutritional needs during prolonged illness• Increased nutritional needs during illness• Nasogastric tube feedings or parenteral nutrition

may be required

• Nutritional care in institutional settings • Periodic reassessment of nutritional status is critical


MyPyramid

• Based on recommendations from the 2005 USDA Dietary Guidelines for Americans

• Includes figure climbing the steps of the pyramid to emphasize exercise in addition to nutrition

• Colored bands on the pyramid represent the recommended proportions of vegetables (green), grains (orange), fruits (red), milk products (blue), meats and beans (purple), and oils (yellow)

• Personalized pyramid • www.mypyramid.gov• Enter age, gender, and activity level


Figure 9-1A


Food Labeling

• People have expressed an increased need to be informed about what they are eating

• Many more foods are now labeled so that the average person can make determinations about the quality and quantity of the nutrients consumed


National Guidelines for Diet Planning

• Many guidelines are available on proper nutrition to maintain health and prevent disease

• Surgeon General’s Report on Nutrition and Health can be used as a basis for dietary planning (Table 9-14)


Figure 9-2


Vegetarian Diets

• Many vegetarians eat all foods except red meat, although some exclude poultry and fish as well • Lactovegetarian diet

• Includes milk, cheese, and other dairy products but excludes meat, fish, poultry, and eggs

• Lacto-ovo-vegetarian diet • Includes dairy products and eggs but excludes meat, fish,

and poultry

• Vegan• Consumes no foods of animal origin


Nursing Assessment of Nutritional Status

• Dietary history• Physical, psychological, social, and medical data that may

affect nutritional status

• Anthropometric data• Height, weight (including weight patterns), and body

composition

• Laboratory data• Serum albumin, total lymphocyte count (TLC),

creatinine/height index, nitrogen balance, mean corpuscular volume (MCV), and transferrin saturation

• Physical examination data


Figure 9-3


Weight Management and Eating Disorders

• Most adults maintain a constant weight but must eat and exercise consistently on a daily basis

• Overweight: obese if weight is 20% or more above ideal body weight

• Underweight: weight is 15% to 20% or more below accepted weight standards

• Eating disorders fairly common among teenage girls and young women, and may persist into adulthood


Anorexia Nervosa

• An eating disorder characterized by self-imposed starvation

• Generally girls in their midteens, although young adult women and men sometimes develop the disorder

• Become obsessed with weight loss; distorted body image


Bulimia

• Characterized by periods of binge eating followed by purging

• May alternate with periods of fasting• Occurs more frequently than anorexia nervosa;

also seen most often in young women


Binge-Eating Disorder

• The intake of excessive calories at least twice a week for 6 months


Nutritional Support with Supplemental Feedings

• Sometimes a person’s nutritional needs cannot be met by oral feeding and a nutritional supplement is required• Liquid or powdered milk, powdered whole eggs, and

powdered egg albumin as concentrated protein sources

• Examples: Ensure, Compleat, Sustacal, Criticare HN, Pulmocare, Trauma Cal, Travasorb HN, and Travasorb Renal


Enteral Tube Feedings

• Bypass the mouth and deliver nutrients directly into the stomach or small intestine through inserted tubes

• Tubes can be inserted into the stomach, duodenum, or jejunum through the nose or through the abdominal wall

• Complications• Nausea or vomiting, diarrhea, gastrointestinal

bleeding, aspiration pneumonia, hyperkalemia, hyponatremia, hyperglycemia, or nutritional deficiency

• Dumping syndrome


Figure 9-4


Parenteral Nutrition

• Peripheral parenteral nutrition• Intravenous therapy• May be composed of dextrose (5%-10%), amino

acids, vitamins, minerals, and electrolytes • At most it supplies 1800 kcal/day


Parenteral Nutrition

• Total parenteral nutrition• Used for patients who are unable to obtain

adequate nutrition enterally or with PPN • Can supply up to 4000 kcal/day • Complications: pulmonary complications, injury to

the veins and arteries surrounding the TPN catheter site, air embolism, infection, electrolyte imbalance, mineral deficiency, hyperglycemia, and, if treatment is ended suddenly, rebound hypoglycemia


Transitional Feeding

• Nutrition changed from one method to another• Important that it be done gradually

• Nutritional recovery syndrome my occur if given food too quickly

• Moderate in carbohydrates, low in sodium, lactose free, and supplemented with phosphorus and potassium


Transitional Feeding

• Parenteral to oral or enteral feeding• Continue the parenteral feeding; as patient is able to

tolerate the oral or enteral feedings, parenteral feedings can be tapered off

• Enteral to oral feedings• Change the enteral feeding from a continuous drip

to an intermittent feeding; allows patient to get hungry

1Elsevier items and derived items © 2007 by Saunders, an imprint of Elsevier, Inc. Chapter 9 Nutrition.

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