Lecture 6-2024 Macronutrients PDF

MACRONUTRIENTS Dr. Sarray Sameh, PhD Macronutrients The essential nutrients that are needed for growth and energy: Carbohydrates Proteins Fats Water Carbohydrates and fats are the principal energy sources Dietary proteins serve many roles including energy production Carbohydrates 1-Monosaccha...

MACRONUTRIENTS Dr. Sarray Sameh, PhD Macronutrients The essential nutrients that are needed for growth and energy: Carbohydrates Proteins Fats Water Carbohydrates and fats are the principal energy sources Dietary proteins serve many roles including energy production Carbohydrates 1-Monosaccharides: e.g. glucose (fruit, sweet corn, honey..) and fructose (honey, fruit) 2-Disaccharides: most abundants are sucrose (glucose+fructose) can be found in table sugar, maltose (2 molecules of glucose) found in significant quantities in beer and lactose found in milk (glucose+galactose) 3-Polysaccharides: complex carbohydrates that do not have sweet taste e.g. starch and glycogen 4-Fibers: Non digestible polysaccharides Provides little energy Add Bulk to the diet, delay gastric emptying: sensation of fullness Lower LDL cholesterol Soluble  Pectins, beta-glucan, some gums…  Resistant to digestion and absorption in the human small intestine, but are completely, easily fermented by intestinal bacteria Insoluble  Cellulose, lignin (in plants)…  passes through the digestive track largely intact.  Not easily fermented  helps speed up the transit of food in the digestive tract and helps prevent constipation REQUIREMENT FOR CARBOHYDRATES o Carbohydrates are not essential nutrients (the carbon skeletons of most amino acids can be converted into glucose); o Absence of dietary carbohydrate leads to ketone body production and degradation of body protein o o Adults should consume 45–65% of their total calories from carbohydrates. They produce 4 kcal/g, the same as protein and less than one half that of fat. Dietary carbohydrates and blood glucose  The glycemic index (GI): represents the total rise of sugar level in in a person's blood following consumption of food particularly carbohydrate- rich food in comparison to increase in blood glucose level on consumption of 50 grams of pure glucose.  Foods with a high GI contain rapidly digested carbohydrate, which produces a large rapid rise and fall in the level of blood glucose  In contrast, foods with a low GI contain slowly digested carbohydrate, which produces a gradual, relatively low rise in the level of blood glucose. Food with low GI are useful in dietary management of diabetes ,and give a feeling of satiety for a longer period (help weight control); In general, whole grains, legumes, fruits, vegetables have low GI’s   Dietary fats  Provide essential fatty acids, which cannot be synthesized by the body. Their biologic properties are determined by the chemical nature of the constituent fatty acids: the presence or absence of double bonds, the number and location of the double bonds, and the cis- trans configuration of the unsaturated fatty acids. Dietary fats include triglycerides, phospholipids and cholesterol. Dietary triglycerides can be utilized by many tissues of the body as an energy source. Dietary cholesterol: cannot be used as a source of energy but is metabolized to bile salts and steroid hormones. Depending on their chemical structure, fats are often classified into 3 different categories:  Saturated fatty acids  Unsaturated fatty acids a. monounsaturated b. polyunsaturated  Cholesterol Saturated Fats  Saturated fats are fats without any double bond  Used by the liver to produce cholesterol  Strongly associated with high levels of total plasma cholesterol, LDL cholesterol, and an increased risk of CHD.  Sources: dairy and meat products and some vegetable oils (palm oil).  It is advisable to limit the intake to 10 % of the total calories in the diet. Poly-unsaturated Fats (cont. )  Have two or more double bonds in the carbon chain  Can be subdivided into omega group followed by a number (n-3 and n-6):  The number indicates the location of the first double bond at one end of the carbon chain. The two well known are omega 3 and omega 6 fats n-6- (or omega-6 ) fatty acids: They seem to decrease total and LDL-cholesterol, but they decrease HDL-cholesterol also. However, the benefits of lowering LDLcholesterol is more important medically. Sources include Nuts, avocado, olives, soybeans and various oils a. n-3- ( or omega-3 ) fatty acids: reduce serum triglycerides, lower blood pressure…, have little effect on LDL or HDL cholesterol level. However, they decrease the tendency to thrombosis, and subsequently reduce the risk of cardiovascular disease. Sources include: plants and fish oil. b. Trans fatty acids  Chemically classified as unsaturated fatty acids (some of its double bonds in the trans position) but behave as saturated fatty acids:  They increase LDL-cholesterol (but not HDL), increasing the risk of CHD.  They do not occur naturally in plants but occur in small amounts in animals.  Trans fatty acid are formed during the hydrogenation of liquid vegetable oils  Trans fatty acid are major component of commercial baked products including crackers, cookies, doughnuts, breads, French fries or chicken fried.  The recommended daily intake of trans fatty acids should be less than 2.0 % of total calorie intake. Dietary cholesterol  Found only in animal sources  An increase in dietary cholesterol in humans leads to an increase in LDL-cholesterol  It is recommended to decrease the amount of dietary cholesterol to less than 200 mg/day. -The main role of dietary protein is maintenance of tissue structure, function and integrity. Sources: * Proteins from animal sources (meat, poultry, milk, and fish) high quality because they contain all the essential amino acids in proportions similar to those required for the human tissue proteins synthesis. * Proteins from plant sources: wheat, corn, rice, and beans; have a lower quality than do animal proteins. The RDA for protein is at 0.8 g/kg of body weight; - People who exercise strenuously: benefit from extra protein to maintain muscle mass; a daily intake of about 1 g/kg has been recommended for athletes. - To support growth, infants should consume 2 g/kg/day. -In case of dietary restriction, dietary protein is used as a source of energy after removal of amino group and conversion into glucose or ketoacids and fatty acids. -In case of adequate supply of carbohydrates and fat , excess protein is stored as triglycerides in adipose tissue.  Nitrogen balance is a comparison between the intake of nitrogen (mainly as protein) and the excretion of nitrogen (mainly in the form of undigested protein in feces and urea and ammonia in the urine).  The normal healthy adult should be in equilibrium, with intakes=losses  Positive nitrogen balance: during situations in which tissue growth occurs like child development, pregnancy and in a convalescing adult  Negative nitrogen balance occurs when : (1) dietary intake is insufficient ,or (2) one of the essential amino acids is deficient or lacking in the diet. (3) Under stress condition: burn, injury, sepsis or cancer. Protein energy malnutrition (PEM)  PEM is mostly seen in patients with medical conditions that  decrease appetite or alter how nutrients are digested or absorbed, OR seen in  hospitalized patients with major trauma or infections  Mostly occurs in children or the malnourished elederly  PEM has two extreme forms that are kwashiorkor and marasmus: KWASHIORKOR  Occurs when protein deprivation is relatively greater than the reduction in total calories, resulting in severely decreased synthesis of visceral protein.  In children after weaning at about age 1 year when their diet consists predominantly of carbohydrates.  Symptoms: stunted growth, skin lesions, hypopigmented hair, enlarged fatty liver, edema and decreased serum albumin concentration less than 2 g/dl is a biochemical marker for Kwashiorkor.  Edema results from lack of adequate plasma proteins primarily albumin to maintain the distribution of water between blood and tissues. MARASMUS  Occurs when calorie deprivation is relatively greater than the reduction in proteins.  In children younger than age 1 year when breast feed is supplemented with watery gruels of native cereals that are usually deficient in both proteins and calories.  Symptoms: arrested growth, extreme muscle wasting, loss of subcutaneous fat, weakness and anemia. Individuals with marasmus do not show edema observed in kwashiorkor.  END!