Nutrients and Metabolism (Presentation1) PDF

Part 1—Nutrients Nutrient: substance in food needed for growth, maintenance, repair Five categories ▪ Three macronutrients that make up most of our diet Carbohydrates, lipids, and proteins ▪ Two micronutrients that are equally important, but requiremen...

Part 1—Nutrients Nutrient: substance in food needed for growth, maintenance, repair Five categories ▪ Three macronutrients that make up most of our diet Carbohydrates, lipids, and proteins ▪ Two micronutrients that are equally important, but requirements are small Vitamins and minerals Most nutrients used for metabolic fuel, some for building molecules and cells Water also needed; accounts for ~ 60% by volume of the food we eat Essential nutrients: ~ 40 molecules must be provided by diet We can’t synthesize them in adequate amounts, like the hundreds of other nonessential nutrients we require ▪ Cells (especially liver cells) have ability to convert one type of molecule to another; interconversions allow us to adjust to varying food intakes Part 1—Nutrients Energy value of nutrients measured in kilocalories (kcal) One kcal is amount of heat needed to raise temperature of 1 kg H2O by 1C ▪ 1 kcal = one calorie (C) Carbohydrates and proteins have 4 kcal/g, but lipids have almost 9 kcal/g USDA’s MyPlate: guidelines represented as portions on a dinner plate Food groups represented: ▪ Fruits ▪ Vegetables ▪ Grains ▪ Protein ▪ Dairy Basic dietary principles: Eat only what you need Eat plenty of fruits, vegetables, and whole grains Avoid junk food Carbohydrates Dietary sources Mostly plants, except for milk sugar (lactose) and small amounts of glycogen Sugars (mono- and disaccharides): fruits, sugarcane, sugar beets, honey, milk Starch (polysaccharide): grains and vegetables Insoluble fiber (the cellulose we can’t digest in vegetables) provides roughage that increases bulk of stool and facilitates defecation Soluble fiber (like pectin in apples and citrus) reduces blood cholesterol levels Carbohydrates Uses in the body Glucose is the carbohydrate molecule used by cells to make ATP ▪ Fructose and galactose converted to glucose by liver before entering circulation ▪ Many cells also use fats for energy, but neurons and RB Cs rely almost entirely on glucose (neurons die quickly without it) ▪ Excess glucose converted to glycogen or fat (for later use) Other uses: building nucleic acids (with pentose sugars) and cell’s glycocalyx (with short chain sugars) Carbohydrates Dietary requirements Recommended daily intake is 45–65% of total calories ▪ Typical American adult at  46% Should consist mostly of complex carbohydrates (whole grains and vegetables) rather than simple (monosaccharides and disaccharides) ▪ Eating large amounts of refined, sugary foods (“empty calories”) can lead to obesity, as well as nutritional deficiencies Starchy foods (rice, pasta, breads) cost less than high-protein foods (like meat), so carbohydrates often make up greater percentage of diet in low-income groups Lipids Dietary sources Primarily triglycerides (neutral fats) in the form of: ▪ Saturated fats in meat, dairy, some tropical plants (e.g., coconut) ▪ Trans fats in hydrogenated oils (e.g., margarine and shortening) ▪ Unsaturated fats in seeds, nuts, olive oil, and most vegetable oils Cholesterol found in egg yolk, meats, organ meats, shellfish, and milk products ▪ Liver makes  85% of blood cholesterol Two essential fatty acids liver can’t synthesize (but found in most vegetable oils) ▪ Linoleic acid—an omega-6 fatty acid (component of lecithin) ▪ Linolenic acid—an omega-3 fatty acid  Lipids Uses in the body Adipose tissue provides protective cushioning, insulation, energy storage Phospholipids essential part of myelin sheaths (neurons) and cell membranes Cholesterol stabilizes cell membranes; precursor of bile salts and steroid hormones Prostaglandins (regulatory molecules made from linoleic acid) ▪ Role in smooth muscle contraction, regulation of B P, and inflammation Triglycerides provide a major energy source for skeletal muscle and liver cells Help body absorb fat-soluble vitamins Dietary requirements Fats should represent 20–35% of total caloric intake (> 40% in typical American diet) ▪ Limit saturated fats to 10% or less of total fat intake Cholesterol can be synthesized to meet needs (not required in diet) ▪ Many recommend intake as low as possible, especially for those with high blood cholesterol levels, which is associated with cardiovascular (CV) disease Proteins Dietary sources Animal products (eggs, milk, fish, most meats) and soybeans provide complete proteins—meeting all amino acid requirements Legumes, nuts, and cereal grains contain incomplete proteins—low in one or more essential amino acids ▪ Ingested together, cereal grains and legumes provide all essential amino acids Essential Amino Acids Figure 24.2 Essential amino acids Proteins Nitrogen balance Homeostatic state where rate of protein synthesis equals rate of breakdown and loss; amount of nitrogen ingested (via protein) equals amount excreted Positive nitrogen balance: synthesis exceeds breakdown ▪ Normal in growing children, pregnant women, tissue repair Negative nitrogen balance: breakdown for energy exceeds synthesis ▪ Occurs during stress, burns, infection, injury, low quality or quantity of dietary proteins, starvation Dietary requirements Needed to supply essential amino acids (and make nonessential ones) Amount needed depends on age, size, metabolic rate, current nitrogen balance ▪ Rule of thumb: daily intake of 0.8 g per kg body weight Vitamins Vitamins are organic compounds body requires in minute amounts Not an energy source themselves, but needed to use macronutrients that are—dietary carbohydrates, proteins, fats would be useless without vitamins Most are coenzymes (or parts of), which act with an enzyme to carry out a particular reaction; e.g., B vitamins act as coenzymes when glucose is used to make ATP Most must be ingested, except vitamin: D (made in skin) B and K (synthesized by intestinal bacteria) Also, body can convert beta-carotene (orange pigment in carrots) to vitamin A Balanced diet best way to avoid deficiencies No one major food group contains all vitamins Vitamins Two types of vitamins based on solubility Water-soluble vitamins ▪ B complex and C are absorbed with water ▪ B12 absorption requires intrinsic factor (secreted from stomach glands) ▪ No significant storage in body; absorbed vitamins not used by cells are excreted in urine (so problems from excessive intake are rare) Fat-soluble vitamins A, D, E, and K are absorbed with lipids in gut ▪ Problems with lipid absorption can interfere with uptake of fat-soluble vitamins ▪ Stored in body (except for K); excessive intake can cause health problems Free radicals (molecules with unpaired electron) generated during normal metabolism Vitamins A, C, E, and mineral selenium are antioxidants—participants in antioxidant reactions that neutralize dangerous free radicals Megadoses of vitamins not beneficial, and may cause serious health problems (especially fat-soluble vitamins) Vitamins Table 24.2 [cont.] inue d Fat-Soluble Vitamins Vitamin Major Dietary Sources Major Functions In The Symptoms Of Deficiency Or Body Extreme Excess Vitamin A (retinol) Provitamin A (beta-carotene) in Component of visual Blindness, skin disorders, deep green and orange pigments; maintenance of impaired immunity Headache, vegetables and fruits; retinol in epithelial tissues; irritability, vomiting, hair loss, dairy products antioxidant blurred vision, liver and bone damage Vitamin D Dairy products, egg yolk; also Aids in absorption and use Rickets (bone deformities) in made in human skin in presence of calcium and phosphorus children, bone softening in adults of sunlight Brain, cardiovascular, and kidney damage Vitamin E Vegetable oils, nuts, seeds Antioxidant; helps prevent Degeneration of the nervous (tocopherol) damage to cell membranes system Vitamin K Green vegetables, tea; also made Important in blood clotting Defective blood clotting Liver (phylloquinone) by colon bacteria damage and anemia Modified from: Urry et al., Campbell Biology, 12th Edition, © 2021. Reprinted by permission of Pearson Education, I nc., Upper Saddle River, N.J. Minerals Seven minerals required in moderate amounts (plus trace amounts of others): Calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium Like vitamins, work with nutrients for proper body functioning Incorporating minerals into structures makes them stronger ▪ Calcium, phosphorus, and magnesium salts harden teeth and strengthen bone Most ionized in body fluids or bound to organic compounds to form phospholipids, hormones, and various proteins ▪ Iron is essential part of oxygen-binding heme of hemoglobin ▪ Sodium and chloride are major electrolytes in blood ▪ Iodine is necessary for thyroid hormone synthesis Uptake and excretion balanced to prevent toxic overload Natural sodium in foods poses little-to-no health risk; the large amounts added to processed foods and sprinkled on food may cause fluid retention and high BP Mineral-rich foods: legumes and other vegetables, milk, some meats Table 24.3 Minerals in the Body Table 24.3 [cont.] inue d Trace Amounts Required Mineral Major Dietary Sources Major Functions In The Body Symptoms Of Deficiency* Iron (Fe) Meats, eggs, legumes, whole grains, Component of hemoglobin and of electron Iron-deficiency anemia, green leafy vegetables carriers in energy metabolism; enzyme weakness, impaired immunity cofactor Fluorine (F) Drinking water, tea, seafood Maintenance of tooth (and probably bone) Higher frequency of tooth decay structure Zinc (Zn) Meats, seafood, grains Component of certain digestive enzymes Growth failure, skin abnormalities, and other proteins reproductive failure, impaired immunity Copper (Cu) Seafood, nuts, legumes, organ Enzyme cofactor in iron metabolism, Anemia, cardiovascular meats melanin synthesis, electron transport abnormalities Manganese (Mn) Nuts, grains, vegetables, fruits, tea Enzyme cofactor Abnormal bone and cartilage Iodine (I) Seafood, iodized salt Component of thyroid hormones Goiter (enlarged thyroid) Cobalt (Co) Meats and dairy products Component of vitamin BB12 su b12 None, except as B12deficiency Bsub1 2 Selenium (Se) Seafood, meats, whole grains Enzyme cofactor for antioxidant enzymes Muscle pain, possibly heart muscle deterioration Chromium (Cr) Brewers’ yeast, liver, seafood, Involved in glucose and energy metabolism Impaired glucose metabolism meats, some vegetables Molybdenum (Mo) Legumes, grains, some vegetables Enzyme cofactor Disorder in excretion of nitrogen- containing compounds *All of these minerals are also harmful when consumed in excess. Modified from: Urry et al., Campbell Biology, 12th Edition, © 2021. Reprinted by permission of Pearson Education, Inc., Upper Saddle River, N.J. Part 2—Metabolism Metabolism: sum of all biochemical reactions in the body, which involve nutrients Substances are constantly built up (anabolism) and broken down (catabolism) Even at rest, body uses lots of energy for essential activities (like breathing and absorbing nutrients from food)