National University Faculty of Medicine Course: Nutrition and Metabolism Part (5) Nutrition (ME-NUT-224)

Transcription

1 1 National University Faculty of Medicine Course: Nutrition and Metabolism Part (5) Nutrition (ME-NUT-224) Dr. Nagla Abdelgaffar Khalafalla Mobil:

2 2 Nutrition Introduction Nutrients are the constituents of food necessary to sustain the normal functions of the body. All energy is provided by three classes of nutrients (Macronutrients) namely: o Fats o Carbohydrates o Proteins The intake of these energy-rich molecules is larger than that of other dietary nutrients (Micronutrients) like vitamins and minerals which are needed in lesser amounts. It is necessary to know the kinds and amounts of macronutrients that are needed to maintain optimal health and prevent chronic diseases in adults.

3 3 Dietary Reference Index (DRI) It is an Estimate of the amount of nutrients required to prevent deficiencies and maintain optimal health and growth. It consists of four dietary reference: 1- Estimated Average Requirements (EAR) 2- Recommended Dietary Allowance (RDA) 3- Adequate Intake (AI) 4- Tolerable Upper Intake level (UL) These are standards for the intake of nutrients designated for: o Specific age groups o Physiologic state o Gender 1. Estimated Average Requirements (EAR) Is the average daily nutrient intake level estimated to meet the requirement of one half of the healthy individuals in a particular life stage and gender group. It is useful in estimating the actual requirement in groups and individual. 2. Recommended Dietary Allowance (RDA) Is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all 97-98% the individuals in a life stage and gender group.

4 4 3. Adequate Intake (AI) Is based on estimates of nutrient intake by a group e.g. the AI for young infants for whom human milk is the recommended sole source of food for the first 4-6 months (full-term infant who are extensively fed). 4. Tolerable Upper Intake level (UL) Is the highest average daily nutrient intake level that is likely to pose no risk of adverse health effects to almost all individual in the general population. If the intake increased above UL, potential risk of adverse effects may increase. Using DRI Most nutrients have a set of DRI. Usually a nutrients have an EAR and corresponding RDA are set by: o Age o Gender o Physiologic factors (pregnancy and lactation) When the data are not sufficient to estimate EAR or RDA and AI, is designated. Intake below the EAR need to be improved because the probability of adequacy is % or less. Intake between the EAR and RDR need to be improved because the probability of adequacy is less than 98%. Intake at or above the AI can be considered adequate. Intake above AI can be considered adequate. Intake between the UL and the RDA can be considered to have no risk for adverse effects.

5 5 Energy Requirements in Humans The estimated energy requirement is average dietary energy intake predicted to maintain an energy balance, that is; calories consumed are equal to the energy expended. EER: in a healthy adults of a defined age, gender, height- whose weight and level of physical activity are consistent with good health. Differences in the genetics, body composition, metabolism, and behavior make it difficult to accurately predict a person caloric requirements For example : Sedentary adult requires about 30 kcal/kg/day. Moderate active adult requires about 35 kcal/kg/day. Very active adult requires about 40 kcal/kg/day. The daily average requirement for energy that is listed food labels is either or kcal/kg/day Energy content of food Is calculated from the heat re by the total combustion of food in a calorimeter. In kilocalories or calories, also joules are used. o 1 cal = 4.2 J

6 6 How energy is used in the body The energy generated by metabolism of the macronutrients is used for three energyrequiring processes that occur in the body; o Resting metabolic rate o Thermic effect of food o Physical activity Resting metabolic rate (RMR) (formerly Basal Metabolic Rate (BMR) ) The energy expended by an individual in a resting, post absorptive state (RMR). This energy is present in: o Respiration o Blood flow o Ion transport o Maintenance of cellular integrity In adult RMR is about 1,800 kcal for men (70 kg), 1,300 for women (50 kg). From % of the daily energy expenditure in sedentary individual is attributable to the RMR.

7 7 Thermic effect of food The production of heat by the body increases as much as 30% above the resting level during the digestion and absorption of food is known as diet induced thermogenesis, and its amount is 5-10 % of the total energy expenditure. Physical Activity Muscular activity provides the greatest variation in energy expenditure. The amount of the energy consumed depends on the duration of all activities. Generally: a sedentary person requires about % more than resting caloric requirement for energy balance. Whereas highly active individual may require 100 % or more calories above RMR. Acceptable Macronutrients Distribution Range (AMDR) Is the range of intakes for a particular macronutrient that is associated with reduced risk of chronic diseases. AMDR ranges for adults are: Carbohydrates: % Proteins: % Fats: %

8 8 Macronutrients requirements in human All energy in the diet is provided by three nutrients: lipids, carbohydrate and proteins: Lipids 1. Triacylglycerols constitute more than 90% of total dietary lipids. Importance of lipids in diet: a. Energy production: however, this is not essential function as other dietary sources can supply energy. b. Essential polyunsaturated fatty acids: lenoleic, lenolenic and arachidonic acids: These acids cannot be synthesized by the body and should be taken in diet. They have many biological functions as eicosanoids synthesis. They are required for membrane structure (see lipids chemistry). c. Fat soluble vitamins (A, D, K and E): are supplied and absorbed with lipids. d. Palatability of food: the presence of fats in food makes it more palatable.

9 9 Types of lipids in diet: a. Fats from plant sources: 1. Triacylglycerols obtained from plants generally contain more unsaturated fatty acids than those from animal sources. They are liquid at room temperature. 2. Coconut and palm oils are exceptions and consisted mainly of saturated fatty acids. 3. Olive oil and canola oil are fats rich in more unsaturated fatty acids. b. Corn oil and soybean oil are fats rich in polyunsaturated fatty acids. b. Fats from animal sources: 1. They are derived from milk products, hard margarine, lards and meat remnants. 2. They are generally contain saturated fatty acids. c. Fishes are exception, whose fatty acids are largely unsaturated. d. Cholesterol: found only in foods of animal origin. It is very rich in egg yolk and organ meats. Lipids and diseases: a. Coronary heart diseases: 1. There is a strong correlation between coronary heart diseases, myocardial infraction, blood cholesterol and consumption of fat particularly of saturated fat.

10 10 2. Ingestion of saturated fatty acids in diet is associated with high level of plasma cholesterol and LDL-cholesterol Atherosclerosis. 3. Ingestion of ω-6 and ω -3 polyunsaturated and monounsaturated fatty acids lower plasma cholesterol protect against atherosclerosis. b. Cancer: High Intakes of saturated fats are associated with Increased risk of certain cancers, especially cancer of colon, prostate and breast.

11 11 Carbohydrate Carbohydrates in the diet are classified as monosaccharides, disaccharides, polysaccharides and fibers. The metabolism of carbohydrate is discussed in part II. a. Monosaccharides: glucose and fructose are principle monosaccharides present in food. 1. Glucose: is abundant in fruits e.g. grape, sweet corn, corn syrup and honey. 2. Fructose (free): is found together with free glucose and sucrose in honey and fruits. b. Disaccharides: 1. Sucrose (glucose + fructose): ordinary table sugar. Also it is abundant in cane, beef, molasses and maple syrup. 2. Lactose (glucose + galactose): milk sugar. 3. Maltose (glucose + glucose): it is a product of enzymatic digestion of polysaccharides. It is found also in beer and malt liquors. c. Polysaccharides: Starch: polymer of glucose that do not have sweet taste. It is found in abundant in plants as wheat, other grains, potatoes, dried peas, beans and vegetables.

12 12 d. Fiber: Dietary fiber consists of non-digestible carbohydrates including cellulose, protein, gums, lignin and pentosans. Dietary fiber provides no energy, but has the following functions: 1. It adds bulk to diet, making little room for more traditional high fat and high cholesterol food. 2. Fiber can absorb 10 to 15 times its own weight in water, drawing fluid into the lumen of the intestine. This prevents constipation by: Increasing bowel motility. Producing of larger and softer feces. 3. The biding properties of fiber can result in decrease absorption of toxic compounds, including carbon substances causing cancers.

13 13 4. A high fiber diet is associated with reduced incidence of some disease e.g. cancer colon. 5. The more soluble fibers as gum and pentosans found in legumes and fruits, lower blood cholesterol, possibly by binding bile acids. 6. The more soluble fibers also slow stomach emptying, and they delay and alternate the postprandial rise in blood glucose. This leads to decrease the amount of insulin required. This effect is beneficial to diabetics dieters. 7. However, dietary fiber can bind trace elements (e.g. zinc) and decrease the absorption of fat soluble vitamins. Thus, supplementation of the diet with moderate and not excess fiber is recommended. Requirements for carbohydrates: a. Carbohydrate is not an essential nutrient, because the carbon skeletons of amino acids can be converted into glucose (gluconeogenesis). b. However, the absence of carbohydrates leads to: Ketone bodies production. Degradation of body proteins. c. Thus, minimal daily intake of carbohydrate ( grams) is recommended in human to prevent ketosis and save body proteins.

14 14 Proteins Dietary proteins provide the body with essential amino acids: a. Ten of the 20 amino acids needed for the synthesis of body proteins are essential. That is, they cannot be synthesized in humans, and must be taken in diet. b. Of ten essential amino acids, eight are essential at all times, whereas two (arginine and histidine) are required only during periods of rapid tissue growth characteristic of childhood or recovery from illness. Biological value of proteins: It is the ability of protein to provide the essential amino acids required for tissue maintenance. a. Protein from animal sources: egg albumin, meat, poultry, milk, fish have a high biological value because they contain all essential amino acids. b. Proteins from plant sources: proteins from wheat, corn, rice and beans have a lower biologic value than animal proteins. That is because they are usually deficient in some essential amino acids. e.g. corn is deficient in lysine. A mixture of plant food may compensate each other. Nitrogen balance: Nitrogen balance means that nitrogen intake is equal to nitrogen loss from the body. 1. Nitrogen Intake: Nitrogen is taken in the form of dietary proteins. Every 100g protein contain 16 g nitrogen. 2. Nitrogen loss: Nitrogen is lost from the body through: o In urine: Urea (main solute) Uric acid Hippuric acid Ammonia Creatinine Creatine g/d 0.5 g/d 0.7 g/d 0.7 g/d g/d gld

15 15 o In feces: One gram I day is excreted in feces. o In milk and menstrual fluids in female. Positive and negative nitrogen balance: 1. Positive nitrogen balance: means that nitrogen intake is greater than nitrogen loss. It occurs in conditions where the formation of tissue proteins is increased e.g. growing children and muscle training. 2. Negative nitrogen balance: means that nitrogen intake is less than nitrogen loss. It occurs in conditions where breakdown of tissue proteins is increased e.g. diabetes mellitus and starvation. Protein-calorie malnutrition: a. In developed countries, protein-calorie malnutrition is seen most frequently in hospital patients with chronic illness or in individuals who suffer major trauma, severe infection, or the effects of major surgery. Such highly catabolic patients frequently require intravenous administration of nutrients. b. In under developed countries, an inadequate intake of protein and/or energy may be observed. 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 malnutrition are Kwashiorkor and marasmus. 1. Kwashiorkor: This is a disease resulting from deficiency of dietary protein only. It leads to growth retardation, anemia, edema, vomiting and anorexia (loss of appetite). 2. Marsmus: this is a disease resulting from deficiency of dietary protein together with dietary carbohydrate and fat. 3. Malnutrition of cancer and AIDs: Patients with cancer, HIV infection (AIDS) and a number of chronic diseases are frequently undernourished. This condition is called cachexia. It is due to: o Increased catabolism of tissue proteins due to secretion of cytoklnes in response to cancer and infection. o Patients are hypermetabollc with high basal metabolic rate (BMR). This due to consumption of excess ATP. o Patients are thermogenic (feeling of hotness) due to increased stimulation of uncoupler proteins by cytoklnes. This leads to producing energy without Incorporation it into ATP synthesis.

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17 17 Food Pyramid