SOURCES OF ENERGY MACRONUTRIENT Macronutrients include n Carbohydrates

SOURCES OF ENERGY : MACRONUTRIENT - Macronutrients include: n Carbohydrates. n Fats. n Proteins. - Carbohydrates and Fats are the principal energy sources. - Dietary proteins serve many roles including energy production.

FACTORS EFFECTING ENERGY EXPENDITURE - There are four principal factors that affect individual energy expenditure: n Surface area (which is related to height and weight) n Age (reflects growth and lean muscle mass) n Sex (women have a lower BMR due to lower % of lean muscle mass and the effects of female hormones on metabolism). n Activity level : The long term effect is more important than the immediate one. It leads to an increase in lean muscle mass and hence BMR.

EFFECT OF BODY COMPOSITION ON BMR

Acceptable Macronutrient Distribution Range (AMDR) Ø AMDR is a way to express the % of calories from macronutrients associated with reduced risk of chronic diseases. Ø Adults ≥ 19 years: % of daily Ø calories Ø Ø Ø Carbohydrates 45 - 65 Fats 20 - 35%(goal< or= 30%) Proteins 10 -

Ø The ranges were designed to ensure that micronutrients are sufficiently taken in the diet. Ø Diets that are very low in either carbohydrates or fats are likely to be deficient in one or more of the essential micronutrients. Ø Diets that are very low in protein lead to loss of lean muscle mass.

CARBOHYDRATES

Ø Classification of carbohydrates: Ø 1 -Monosaccharide e. g. glucose and fructose Ø 2 - Disaccharides e. g. sucrose, maltose and lactose Ø 3 - Polysaccharides e. g. starch and glycogen Ø 4 -Non starch polysaccharides (Fiber) : components of dietary plants that cannot be broken down by human digestive enzymes, e. g. cellulose and pectin.

Ø Importance of carbohydrates: Ø A- It is the major source of energy in most of the tissues, allowing protein to be used for growth and maintenance (protein- sparing) Ø B- The only source of energy for RBCs, and is also needed for proper brain function. Ø C- A small amount is needed to prevent ketosis. Ø D- Fiber has several beneficial effects on health.

Dietary Fiber Ø Several different types. (Table-2) Ø Each has different chemical and physical properties, and different effects on body function or metabolism. Ø Some are partially broken down by intestinal bacteria. Ø Those that have been shown to have beneficial effects in humans are termed functional fiber. Ø Ø Recommended intake(AI) for total fiber: : 38 g/d for men ages 14 - 50 y;

Carbohydrate and blood glucose: The pattern of the rise in blood glucose level differs after the intake of different types of carbohydrate containing foods. Ø The term glycemic index (GI) was introduced to compare the effect of different types of food on blood glucose. Ø

Glycemic index (GI) is defined as: “The area under the blood glucose curve seen after ingestion of meal with carbohydrate-rich food, compared with the area under the blood glucose curve observed after a meal consisting of the same amount of carbohydrate in the form of glucose or white bread. ” Ø Food with low GI are useful in dietary management of diabetes , and give a feeling of satiety for a longer period (help weight control) Ø

Ø In general, whole grains, legumes, fruits, vegetables have low GI’s (lower than the same amount of white rice) Ø Amylose form of starch has lower GI than amylopectin Ø It was found that the processing of grains increase their GI

Factors Influencing GI Not only the type and amount of CHO that affects the GI, it was found that it is affected by many other factors including: Ø Ø Nature of starch Ø The presence of fat, protein, fiber Ø The way of food preparation

FATS

Dietary Fats n n Dietary fats include : triglycerides, phospholipids and cholesterol. Triglycerides are quantitatively the most important class of dietary fats. Their biologic properties are determined by the chemical nature of the constituent fatty acids , in particular, 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.

Importance of Dietary Fats n n Triglycerides can be utilized by many tissues of the body as an energy source. Fats provide a vehicle delivering fat soluble vitamins to the body. A fat free diet would lead to deficiency of these vitamins. Fats provide essential fatty acids , which cannot be synthesized by the body. A very low fat diet could lead to deficiency of these acids. Dietary cholesterol: cannot be used as a source of energy , but is metabolized to bile salts and steroid hormones.

Dietary Fats and Plasma Lipids Saturated fat: Consumption of saturated fats is strongly associated with high levels of total plasma cholesterol and LDL cholesterol, and an increased risk of CHD. n The main sources of saturated fatty acids are dairy and meat products and some vegetable oils , such as coconut and palm oils. It is advisable to limit the intake to<10% of total calories. A goal of 7% is suggested to lower the risk of CHD. n

Dietary Fats and Plasma Lipids ( continue ) n Monounsaturated fatty acids: Substitution of saturated fatty acids with monounsaturated fatty acids (from plant sources , such as olive oil) help to decrease total and LDLcholesterol , without affecting the HDLcholesterol or the triglycerides level. n It is recommended that monounsaturated fatty acids should constitute >10 % of the total calories in the diet.

Dietary Fats and Plasma Lipids ( continue ) n Polyunsaturated fatty acids: they are derived from plant sources and fish. An intake of 10% of total calories is recommended. n Their effects are influenced by the position of the double bonds within the molecule. a-n-6 - (or omega-6 ) fatty acids also seem to decrease total and LDLcholesterol when used instead of saturated fatty acids , but they decrease HDL-cholesterol also. However , the benefits of lowering LDL-cholesterol is more important medically. Nuts , avocado , olives , soybeans and various oils are common sources. b- n-3 - ( or omega- 3 ) fatty acids reduce serum triglycerides, but 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.

Dietary Fats and Plasma Lipids ( continue ) n n Trans fatty acids: they are the fatty acids with some of its double bonds in the trans position, they may be present in natural food as whole milk and diary products , but mostly they are produced by partial hydrogenation of vegetable oil. They increase LDL-cholesterol , increasing the risk of CHD. Trans fatty acids are mainly present in products made from partially hydrogenated oils such as baked products including crackers, cookies, doughnuts, breads, and products like French fries or chicken fried in hydrogenated shortening. The recommended daily intake of trans fatty acids should be less than 2. 0 % of total calorie intake.

Dietary Fats and Plasma Lipids ( continue ) n Dietary cholesterol: It is only from animal sources n Increased dietary cholesterol leads to significant increase in total cholesterol in animal , but this is not so obvious in human. n An increase in dietary cholesterol in humans leads to an increase in LDL-cholesterol which differs from person to person. n It is recommended to decrease the amount of dietary cholesterol to less than 200 mg/day.

Dietary Fats and Plasma Lipids ( continue ) n Plant sterols: Found in many plant sources (e. g. soybean ) , and some margarines. n Reduce plasma LDL cholesterol by interfering with absorption of dietary cholesterol n

PROTEIN

The Role and Fate Of Dietary Proteins -The main role of dietary protein is maintenance of tissue structure , function and integrity. -Some amino acids are precursors of biologically active compounds, e. g. epinephrine, serotonin. -Incase of dietary restriction dietary protein is used as a source of energy after removal of amino group and conversion into glucose or keto acids and fatty acids. -Incase of adequate supply of carbohydrates and fat , excess protein is stored as triglycerides in adipose tissue.

Protein Intake and Nitrogen Balance 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). n The normal healthy adult should be in equilibrium , with intake=losses. n

Ø Positive nitrogen balance occurs in significant degree during child development, during pregnancy and in a convalescing adult when there is accumulation of proteins in the body. Ø 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. Ø Negative nitrogen balance can occur when the body is under stress condition as in cases of burn, injury, sepsis or cancer , where there is increased amount of nitrogen excretion.

In other words:

Positive Nitrogen Balance

Negative Nitrogen Balance 1. Stress 2. Decreased Intake 3. Lack of an essential AA

Requirements and Adequacy of Dietary Proteins -A certain amount of protein is needed daily in the diet as it cannot be stored in the body. -Proteins from different sources differ in their composition and content of the essential amino acids, hence they are not equally useful as building blocks for proteins in our body. -The usefulness of the protein is expressed in terms of either net protein utilization (NPU) or biological value (BV).

Requirement and Adequacy of Dietary Proteins (continue) n NPU= N retained X 100 N intake = N intake – N output X 100 N intake n BV= N retained N absorbed X 100

Protein Quality Proteins with high BV or NPU are of higher quality. n NPU of dietary proteins varies according to source. n Proteins from animal sources are of higher quality, e. g. albumin NPU=91%, beef NPU=67%. n Vegetable proteins have lower quality, NPU for gluten= 42% n

Recommended Dietary Allowance Assuming adequate calorie intake and 75% efficiency of utilization , which is typical of the mixed protein in the average diet , the recommended protein intake is 0. 8 g / kg body wt/day. n This should be increased on a vegetarian diet with lower efficiency. n Protein requirements are increased during growth and recovery following an illness (table 3) n

Vegetarian Diet and Adequate Protein Intake Ø Vegetable proteins are often low in one or more essential amino acids , for example legumes contain low amount of Met, while grains are low in Lys. Ø Therefore, to provide an adequate vegetarian diet that contains all of the required amino acids , two or more proteins must be consumed together to complement one another in the missing amino acids. For example, beans which contain low amount of Met but rich in Lys , should be eaten with corn , which is low in Lys. (Mexican food) Ø The low amino acid is termed the limiting amino acid