Lecture 37: Principles of Nutrition (3) PDF

Lippincott’s illustrated reviews Chapter 27 – Page 365 Lecture 37 Principles of Nutrition (3) 1  Specific Objectives By the end of this lecture students can be able to: Explain the importance of fibers in the man diet. Differentiate between positive and...

Lippincott’s illustrated reviews Chapter 27 – Page 365 Lecture 37 Principles of Nutrition (3) 1  Specific Objectives By the end of this lecture students can be able to: Explain the importance of fibers in the man diet. Differentiate between positive and negative nitrogen balance. Discuss different reasons for malnutrition diseases. 2  Dietary carbohydrates The primary role of dietary carbohydrate is to provide energy (4 kcal/g). Carbohydrates are not inherently fattening. 3 4  Classification of carbohydrates in food 1. Monosaccharides: Glucose is abundant in fruits, sweet corn, corn syrup, and honey. Free fructose is found together with free glucose and sucrose in honey and fruits. 5 2. Disaccharides: Sucrose (glucose + fructose) is ordinary “table sugar,” and is abundant in molasses and maple syrup. Lactose (glucose + galactose) is the principal sugar found in milk. Maltose (glucose + glucose) is a product of enzymic digestion of polysaccharides. The term “sugar” refers to monosaccharides and disaccharides. “Added sugars” are those sugars and syrups added to foods during processing or preparation. 6 3. Polysaccharides: Polymers of glucose which do not have a sweet taste. Starch is an example of a complex carbohydrate that is found in abundance in plants. Common sources include wheat and other grains, potatoes, dried peas and beans, and vegetables. 7 4. Fiber: Dietary fiber is defined as the nondigestible carbohydrates present intact in plants. It resistant to digestion and absorption in the human small intestine, but is completely or partially fermented to short-chain fatty acids in the large intestine. 8 Function of fiber: Dietary fiber provides little energy. Fiber can absorb 10–15 times its own weight in water, drawing fluid into the lumen of the intestine and increasing bowel motility. Soluble fiber delays gastric emptying and can result in a sensation of fullness. This delayed emptying also results in reduced peaks of blood glucose following a meal. 9  Fiber lower LDL cholesterol levels Also, fiber rich diets decrease the risk for constipation and hemorrhoids. The recommended daily fiber intake (AI) is 25 g/day for women and 38 g/day for men. 10  Requirements for carbohydrate The RDA for carbohydrate is set at 130 g/day for adults and children, based on the amount of glucose used by carbohydrate-dependent tissues, such as the brain and erythrocytes. Adults should consume 45–65% of their total calories from carbohydrates. 11 Simple sugars and disease There is no direct evidence that the consumption of simple sugars is harmful. Diets high in sucrose do not lead to diabetes or hypoglycemia and not to inherently fattening. However, there is an association between sucrose consumption and dental caries, particularly in the absence of fluoride treatment. 12  Dietary protein A. Quality of proteins The quality of a dietary protein is a measure of its ability to provide the essential amino acids required for tissue maintenance. 13 1. Proteins from animal sources: Proteins from animal sources (meat, poultry, milk, and fish) have a high quality because they contain all the essential amino acids in proportions similar to those required for synthesis of human tissue proteins. 14 2. Proteins from plant sources: Proteins from wheat, corn, rice, and beans have a lower quality than do animal proteins. For example, wheat (lysine-deficient but methionine-rich) , kidney beans (methionine-poor but lysine-rich), so we can combine both to produce an improved biologic value. 15 B. Nitrogen balance Nitrogen balance occurs when the amount of nitrogen consumed equals that of the nitrogen excreted in the urine, sweat, and feces. 16 1. Positive nitrogen balance: This occurs when nitrogen intake exceeds nitrogen excretion. It is observed during situations in which tissue growth occurs, for example, in childhood, pregnancy, or during recovery from an sever illness. 17 2. Negative nitrogen balance: This occurs when nitrogen loss is greater than nitrogen intake. It is associated with 1. inadequate dietary protein, 2. lack of an essential amino acid, or 3. during physiologic stresses, such as trauma, burns, illness, or surgery. 18  Requirement for protein in humans The RDA for protein is 0.8 g/kg of body weight for adults, or about 56 g of protein for a 70-kg individual. 19  People who exercise strenuously on a regular basis may benefit from extra protein to maintain muscle mass; a daily intake of about 1 g/kg has been recommended for athletes. Women who are pregnant or lactating require up to 30 g/day in addition to their basal requirements. To support growth, infants should consume 2 g/kg/day. 20 1. Consumption of excess protein: There is no physiologic advantage to the consumption of more protein than the RDA. Excess protein provide energy or acetyl coenzyme A for fatty acid synthesis. When excess protein is eliminated from the body as urinary nitrogen, it is often accompanied by increased urinary calcium, increasing the risk of nephrolithiasis and osteoporosis. 21 2. The protein-sparing effect of carbohydrate: carbohydrate is considered to be “protein- sparing,” because it allows amino acids to be used for repair and maintenance of tissue protein rather than for gluconeogenesis. If carbohydrate intake is less than 130 g/day, substantial amounts of protein are metabolized to provide precursors for gluconeogenesis. 22 Protein energy (calorie) malnutrition (PEM) In developed countries, PEM is most frequently seen in patients with: 1. Medical conditions that decrease appetite or alter how nutrients are digested or absorbed. 2. In hospitalized patients with major trauma or infections. PEM may also be seen in children or the elderly who are malnourished. 23  In developing countries, an inadequate intake of protein and/or energy is the primary cause of PEM. Affected individuals show a variety of symptoms, including a depressed immune system with a reduced ability to resist infection. Death from secondary infection is common. Two extreme forms of PEM are kwashiorkor and marasmus. 24 1. Kwashiorkor: Kwashiorkor occurs when protein deprivation is relatively greater than the reduction in total calories. Protein deprivation is associated with severely decreased synthesis of visceral protein. Kwashiorkor is frequently seen in children after weaning at about one year of age, when their diet consists predominantly of carbohydrates. 25  Typical symptoms include stunted growth, edema, skin lesions, depigmented hair, anorexia, enlarged fatty liver, and decreased plasma albumin concentration. Edema results from the lack of adequate plasma proteins to maintain the distribution of water between blood and tissues. Edema may mask muscle loss. 26 2. Marasmus: Marasmus occurs when calorie deprivation is relatively greater than the reduction in protein. It usually occurs in children younger than 1 year of age when breast milk is supplemented with watery gruels of native cereals that are usually deficient in protein and calories. 27  Typical symptoms include arrested growth, extreme muscle wasting (emaciation), weakness, and anemia. Victims of marasmus do not show the edema or changes in plasma proteins observed in kwashiorkor. 28 Reference Book: Champe, P. C., Harvey, R. A. and Ferrier, D. R., 2005. Biochemistry “Lippincott’s Illustrated Reviews”, 5th or 6th Edition 29