Nutrition and Metabolism 2023-2024 PDF

Nutrition It is the science of food and its relationship to health. It is concerned primarily with the part played by nutrients in body growth, development and maintenance. A nutrient is a chemical substance in food that helps maintain the body. Some provide energy. All help in building cells and...

Nutrition It is the science of food and its relationship to health. It is concerned primarily with the part played by nutrients in body growth, development and maintenance. A nutrient is a chemical substance in food that helps maintain the body. Some provide energy. All help in building cells and tissues, regulate bodily processes such as breathing. The word nutrient is used for specific dietary constituents such as proteins, vitamins and minerals. Good nutrition means “maintaining a nutritional status that enables us to grow well and enjoy good health.”  Variables which affect nutrient needs: 1. Age 4. Climate 2. Gender 5. Health 3. Activity Level 6. State of nutrition  Classes of Nutrients Macronutrients: Micronutrients: -Carbohydrates = 4 cal/g -Vitamins = 0 cal/g -Proteins = 4 cal/g -Minerals = 0 cal/g -Fats = 9 cal/g -Water = 0 cal/g Definition of a Calorie (cal):A unit of measure for energy in food  Carbohydrate Carbohydrate is the main source of energy, providing 4 cal per one gram. Carbohydrate is also essential for the oxidation of fats and for the synthesis of certain non- essential amino acids Sources of carbohydrates There are three main sources of carbohydrate: starches, sugar and cellulose. The carbohydrate reserve of a human adult is glycogen. This reserve is rapidly exhausted when a man is fasting. If the dietary carbohydrates do not meet the energy needs of the body, protein and glycerol from dietary and endogenous sources are used by the body to maintain glucose homeostasis. Carbohydrates are carbon compounds that contain large quantities of hydroxyl groups, also contain either an aldehyde group or a ketone groups Functions of carbohydrates : 1- Serve as source of energy 2- Enter in the structure of glycoproteins and glycolipids that enter the structure of cell membrane and membrane receptors 3- Pentose sugars (ribose and deoxyribose) enter in the structure of nucleic acid, free nucleotides (ADP and ATP) and coenzymes (NAD and FAD) Classification of carbohydrates We may classify the carbohydrates according to the number of structural units into: Monosaccharides: contain a single polyhydroxy aldehyde or ketone unit (saccharo is Greek for “sugar”) (e.g., glucose, fructose). Disaccharides: consist of two monosaccharide units linked together by a covalent bond (e.g., sucrose). Oligosaccahrides: contain from 3 to 10 monosaccharide units (e.g., raffinose). and Polysaccharides contain very long chains of monosaccharide units, which may be either in straight or branched chains (e.g., cellulose, glycogen, starch), they are not reducing sugars.  Proteins Proteins are complex organic nitrogenous compounds, providing 4 cal per one gram. Proteins are made of monomers called amino acids (a.a). They also contain sulfur and, in some cases, phosphorous and iron. There are about 20 different amino acids which are found in human body. There are 8 a.a are termed “essential” as they are not synthesized in human body and must be obtained from dietary protiens. Protein nutrition status is measured by Serum Albumin Concentration. It should be more than 3.5 g/dl. Less than this concentration indicates to malnutrition Since long, the proteins have been traditionally divided into two well-defined groups: animal proteins and plant proteins. Animal proteins are the proteins derived from animal sources such as eggs, milk, meat and fish. They are usually called higher-quality proteins because they contain adequate amounts of all the essential amino acids. On the other hand, plant proteins are called lower-quality proteins since they have a low content (limiting amount) of one or more of the essential amino acids.  Essential and non-essential amino acids Essential amino acids Non-essential amino acids Histidine Alanine Isoleucine Aspartate Leucine Cysteine Valine Glutamate Lysine Proline Methionine Glycine Threonine Serine Trуptophan Tyrosine Phenylalanine Ornithine Arginine Asparagine  Function of proteins: 1- They provide the body with nitrogen, sulfur, and some vitamins. 2- Formation of hemoglobin, enzymes, protein hormones and antibodies (immunoglobulins). 3- Formation of supporting structures in the body as bone, cartilage, skin, nails, hair and muscles. 4- They enter in the formation of buffer system of the blood. 5- They include plasma proteins, which carry hormones, minerals and lipids (in the form of lipoprotein complex).  The proteins divided into 3 major groups, based on their composition: simple, conjugated and derived. A. Simple Proteins: This group includes proteins containing only amino acids. B. Conjugated or Complex Proteins or Heteroproteins. These are composed of simple proteins in association with some non-protein substance as the prosthetic factor (non-protein portion). The prosthetic group may be either a metal or a compound. On decomposition with acids, these liberate the constituent amino acids as well as the prosthetic group. Their further classification is based on the nature of the prosthetic group present. C. Derived Proteins: These are derivatives of proteins resulting from the action of heat, enzymes or chemical reagents. This group also includes the artificially-produced polypeptides.  Fats (Lipids) Fats are large molecules made up of elements - Carbon, Hydrogen, Oxygen, providing 9 cal per one gram. Lipids are classified as follows: 1. Simple lipids: Esters of fatty acids with various alcohols. (a) Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state. (b) Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols. 2. Precursor and derived lipids: These are the substances derived from simple and compound lipids by hydrolysis. These include fatty acids, alcohols, mono- and diglycerides, steroids, terpenes and carotenoids. 3. Complex lipids: Esters of fatty acids containing groups in addition to an alcohol and a fatty acid. (a) Phospholipids: Lipids containing, in addition to fatty acids and an alcohol, a phosphoric acid residue. They frequently have nitrogen containing bases and other substituents, eg, in glycerophospholipids the alcohol is glycerol and in sphingophospholipids the alcohol is sphingosine. (b) Glycolipids: Lipids containing a fatty acid, sphingosine, and carbohydrate. (c) Other complex lipids: Lipids such as sulfolipids and aminolipids. Lipoproteins may also be placed in this category. Function of lipids: 1- Energy provision as ATP fat stored as fat- very efficient, making fat from carbohydrate and protein is not very efficient, energy source-can store huge quantities of fat 2- Thermal Insulator: Protective layer in body to help and keep heat losses down 3- Bone strength: Fat acts as support and cushioning for organs and cushioning for bones 4- Fat soluble vitamins cannot be absorbed without fat in the diet 5- Cholesterol and phospholipids are important in maintaining the structure and hence function of cell membrane. Recommended blood lipids Total cholesterol: