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Transcript
HUMAN NUTRITION The basic nutritional needs Supply energy and raw materials for activities and processes in the body Macronutrients - required in large amounts: • carbohydrates • proteins • fats Micronutrients - required in small amounts: • vitamins • minerals Uses of macronutrients Carbohydrates and fats used as a source of energy (protein can also be used for this) Proteins provide the raw materials, or building blocks, required for the synthesis of essential metabolites, growth, and tissue maintenance - to make human proteins Carbohydrates and proteins: 4 calories/gram Fat: 9 calories/gram Carbohydrates Monosaccharides • Simple sugars • Building block of more complex carbohydrates • Glucose - the most abundant Disaccharides Polysaccharides • starch, glycogen • cellulose Glucose During digestion other carbohydrates are broken down or converted to glucose Transported by the blood to all the cells in the body Within cells, respiration breaks down glucose to produce energy necessary to sustain life Other monosaccharides Fructose and galactose have the same chemical make up as glucose, C6H12O6, differing only in the arrangement of the atoms Converted into glucose and metabolized High fructose corn syrup, often preferred because sweeter than sucrose Disaccharides Two monosaccharides chemically joined Sucrose - most common (glucose and fructose) • Table sugar at least 97% pure sucrose • Supplies only calories - no other nutritional value • During digestion broken into glucose and fructose Other disaccharides • Lactose - milk sugar (glucose and galactose) • Maltose (2 glucose molecules) - germinating grains Polysaccharides Also known as complex carbohydrates Hundreds to thousands of sugar units Glucose is the only monosaccharide Distinguished by the way in which the glucose units are joined together, their arrangement, and their number Starch Storage form of glucose found in plants • Seeds, some fruits, tubers, and tap roots • Starch in foods can be traced directly to plant origin: starch in bread or pasta from wheat Starch in the human diet • Grains (wheat, rice, and corn) • Underground crops (potato, sweet potato, & cassava) • Legumes (beans and peas) Broken down into glucose by enzymes Glycogen Body's storage form of glucose in liver and skeletal muscles Excess glucose is stored as glycogen Only a day’s worth of glycogen is stored Carbohydrate loading: eat lots of starchy foods to build glycogen reserves Excess glucose beyond this is generally converted to fat Fiber - other polysaccharides From plant sources Not digestible - provides bulk and other benefits Fruits, vegetables, seeds and whole grains supply most of the fiber in the human diet. Types of dietary fiber Cellulose Lignin Hemicellulose Pectin Gums Mucilages Others Cellulose Principal component of plant cell walls Composed of glucose Humans do not have the enzymes to break the bonds connecting the glucose molecules in cellulose Passes through the digestive tract as roughage Other fibers Pectins and hemicelluloses - also cell wall polysaccharides Pectins also occur in the middle lamella Gums and mucilages are exudates from plants that are used commercially as thickening agents Polysaccharides from red and brown algae are also dietary fiber Dietary fiber grouped into two types Soluble and insoluble - relates to their solubility in water Insoluble fiber includes cellulose and lignin and some hemicelluloses Soluble fiber includes other hemicelluloses, pectins, gums, mucilages, and algal polysaccharides Soluble fiber & Insoluble fiber Gum in oat bran Pectin in apples Believed to lower cholesterol levels in the blood Wheat bran Largely cellulose No cholesterol lowering ability Effective in speeding passage of food through the large intestines May reduce the risk of colon cancer Proteins and essential amino acids Proteins are large complex molecules composed of amino acids 20 naturally occurring amino acids Thousands of different types of proteins During digestion proteins in our food are broken down into the component amino acids by enzymes in the digestive tract and transported in the blood stream Functions of Proteins Type Protein Function Structural Enzymes Hormones Transport Storage Contractile Defensive Support Catalysts Regulation Transport substances Storage of amino acids Movement Protection Examples Collagen and keratin Digestive enzymes Insulin Hemoglobin Ovalbumin in egg white Casein in milk Actin, myosin - muscles Antibodies Essential Amino Acids Role of dietary protein is to supply amino acids for the body to make human proteins All 20 amino acids are necessary for protein synthesis Human body can synthesize 11 amino acids Other nine cannot be made by the body and must come from the diet These nine are called essential amino acids Essential Amino Acids Cannot be stored by the body at all They must be present simultaneously in the diet It is critical to receive all the essential amino acids in each meal Persistent lack of these essential amino acids results in protein deficiency Complete proteins Complete proteins contain all the essential amino acids and in the right proportions Almost all proteins derived from animals are complete proteins Proteins derived from plants are usually incomplete, deficient in one or more essential amino acids Complementary plant proteins Combining complementary plant proteins can supply all essential amino acid Traditional diet of the Mexican Indians, beans and corn, contains complementary proteins • The beans are low in methionine but adequate in tryptophan and lysine • Corn is poor in tryptophan and lysine but contains adequate amounts of methionine Essential and Nonessential Amino Acids Essential Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Nonessential Alanine Asparagine Aspartic Acid Arginine Cysteine Glutamic Acid Glutamine Glycine Proline Serine Tyrosine How much protein do we need? Nutritional recommendations can be based on two criteria • 12% of the total calories consumed should be from proteins (1500 calories diet - 45 grams of protein; 1800 calories - 54 g; 2000 cal - 60 g) • 0.8 g/kg body weight (person weighing 150 lbs -54 g protein; person weighing 100 lbs - 36 g protein; 200 lbs - 72 g protein How much protein in our food? 1 ounce meat - 7 grams protein • 4 ounces turkey - 28 grams protein 1 ounce cheese - 7 grams protein 1 glass milk - 8 grams protein 1/2 cup beans - 6 grams protein 1 slice whole wheat bread- 4 grams protein 1 egg - 8 grams protein 2 TBSP peanut butter - 8 grams protein 1 serving oatmeal - 5 grams protein Malnutrition Chronic hunger and malnutrition are problems in many developing nations Estimates: 15% to 20% of the world's population (around one billion people) suffer from undernutrition or malnutrition Approximately 20 million deaths each year Undernutrition is defined as an insufficient number of calories to maintain daily energy requirements Malnutrition is a quality deficiency in which one or more essential nutrients is lacking even though enough calories Kwashiorkor Protein deficient but sufficient calories Prevalent after weaning when a child no longer receives protein-rich breast milk and is switched to a starchy diet low in protein Symptoms of kwashiorkor • • • • puffy skin swollen belly due to edema reddish-orange cast to the hair dermatitis and listlessness. Marasmus Results from starvation Diet is low in calories and protein Sufferers extremely thin and shriveled (literally skin and bones) Muscles of the body, even the heart muscle, are wasted away as muscle protein is used to supply energy needs Treatment Symptoms of both marasmus and kwashiorkor can be reversed if treated in time In infants and young children, mild mental retardation and stunted growth may be permanent results Vegetarian Diets Ovo-lacto vegetarian Lacto vegetarians Vegans Major difficulty is getting sufficient protein Balance amino acids to avoid protein deficiency Fats One category of lipid Lipids are a diverse group of compounds with a common characteristic of insolubility in water Some fat is necessary in the diet - several vital functions Functions of Lipids Type of Lipid Function Examples Triglyceride Steroid Energy storage Insulation Structural Regulation Phospholipid Structural Animal fat Vegetable oils Subcutaneous fat Cholesterol in membranes Cortisol, Estrogen, Testosterone Phosphatidylcholine in cell membranes Triglycerides Fats and oils 95% of lipids in foods Formed from glycerol and 3 fatty acids Fatty acids Simplest type of lipid Building blocks for triglycerides and phospholipids Body can synthesize most fatty acids Three must be supplied in the diet • Linoleic acid • Linolenic acid • Arachidonic acid Fatty acid Carbon chain with hydrogen attached Different fatty acids vary in the number of carbon and hydrogen atoms Saturated or unsaturated • Saturated fatty acids have all single bonds between carbon atoms • Unsaturated fatty acids have one or more double bonds Saturated Fatty Acid H H H H H H H H H H H H H H H l l l l l l l l l l l l l l l O H - C - C - C - C - C - C - C - C - C - C - C - C - C - C - C - C-OH l l l l l l l l l l l l l l l H H H H H H H H H H H H H H H Monounsaturated Fatty Acid H H H H H H H H H H H H H H H l l l l l l l l l l l l l l l O H - C - C - C - C - C - C = C - C - C - C - C - C - C - C - C - C-OH l l l l l l l l l l l l l H H H H H H H H H H H H H Polyunsaturated Fatty Acid H H H H H H H H H H H H H H H l l l l l l l l l l l l l l l O H - C - C - C - C - C = C - C - C - C - C = C - C - C - C - C - C-OH l l l l l l l l l l l H H H H H H H H H H H Triglycerides Glycerol backbone is common to all Many types of fatty acids occur Nature of the fatty acids determines the properties of the triglyceride Saturated Fat C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C l C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C l C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C Monounsaturated Fat C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C l C-O-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-C l C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C Polyunsaturated Fat C-O-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-C l C-O-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-C l C-O-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-C Fats in Foods Contain a mixture of both saturated and unsaturated fatty acids Saturated fats - contain mostly saturated fatty acids • solid at room temperature - animal fats such as lard, butter, and beef fat Vegetable oils - generally composed of unsaturated fatty acids • liquid at room temperature Vegetable Oils Oils with monounsaturated fatty acids • olive oil, peanut oil, and canola oil Oils with polyunsaturated fatty acids • corn oil, soybean oil, and safflower oil Saturated fats in plants • coconut oil, palm oil, and cocoa butter • consist mostly of saturated fatty acids Hydrogenation In prepared foods with vegetable oils Unsaturated oil has been chemically modified by hydrogenation Adds hydrogen making an unsaturated oil, a saturated fat Converts a liquid oil into a solid fat margarine Saturated vs. unsaturated fats Diets high in saturated fats have been implicated in colon, breast, and prostate cancers Saturated fats increase blood cholesterol levels and are linked to cardiovascular disease Unsaturated fats lower the risk of cardiovascular disease by lowering blood cholesterol levels Cholesterol Type of lipid known as steroid • lipid containing four carbon rings Vital component of cell membranes • therefore needed by all cells Used in the synthesis of sex hormones and several other hormones Cholesterol Synthesized in liver from saturated fatty acids and absorbed from animal foods • If the diet is high in saturated fats, even if it is low in cholesterol, the liver responds by increased cholesterol synthesis Lipoproteins: HDL and LDL LDL - bad cholesterol causing deposits in arteries and leading to heart attacks and strokes Cholesterol Diets high in cholesterol and/or saturated fat contribute to high blood cholesterol levels especially LDLs Unsaturated fats lower blood cholesterol levels • Polyunsaturated fats lower all cholesterol levels including HDLs • Monounsaturated fats lowering total and LDL levels Micronutrients Essential for proper nutrition Required in very small amounts Deficiency symptoms develop when nutrient is lacking Comprise only 1 to 2% of the dry weight There are two categories • organic compounds - vitamins • inorganic compounds - minerals Dietary guidelines 1. Consume only as much energy (kcal) as is expended 2. Increase consumption of complex carbohydrates and "naturally occurring" sugars from 28% of energy intake to 48% 3. Reduce consumption of refined and processed sugars to account for about 10% of total energy intake Dietary guidelines (cont’d) 4. Reduce fat consumption from approximately 40% to about 30% 5. Reduce saturated fat consumption to about 10% of energy intake; polyunsaturated and monounsaturated fats, should each account for 10% 6. Reduce cholesterol consumption to about 300 mg a day 7. Limit sodium intake to about 5 g a day Nutrition Facts Serving Size 1/2 (127 g) Servings Per Container About 3.5 Amount per Serving Calories 100 Calories from Fat 0 % Daily Value* Total Fat 0g Saturated Fat 0g Cholesterol 0mg Sodium 580mg Total Carbohydrates 19g Dietary Fiber 5g Sugars 3g Protein 6 g 0% 0% 0% 24% 6% 20% 12% Vitamin A 0% * Vitamin C 0% Calcium 2% * Iron 8%