Chapter 9

1. Chapter 9 Nutrition

2. 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.

3. Anatomy and Physiology of the Gastrointestinal System

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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%

29. 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

30. 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

31. 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

32. 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)

33. 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

34. 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

35. 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

36. Lipid Function Store energy Maintain healthy skin and hair Carry fat-soluble vitamins Supply essential fatty acids Promote satiety

37. 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

38. 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

39. 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

40. 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

41. 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

42. 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

43. Recommended Dietary Allowance Should contribute 10% to 35% of the macronutrients in the adult diet

44. 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

45. 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

46. Minerals Ultratrace elements Selenium, chromium, copper, manganese, molybdenum, boron, cobalt Ionized forms Sodium, potassium Constituents of organic compounds Phospholipids, hemoglobin

47. 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

48. 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

49. 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

50. 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