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Advanced Nutrition Carbohydrates MargiAnne Isaia, MD MPH CARBOHYDRATES CHO (CARBOHYDRATES) General formula Cn (H20)n CHO 1:2:1 exception: sugar alcohols (Sorbitol, Maltitol, Manitol, Galactitol,Lactitol) oligosaccharides & polysaccharides CHO classification - simple: monosaccharides, hexose: Glucose, Galactose, Fructose, pentose: Ribose; disaccharides: Maltose, Sucrose, Lactose - complex: oligosaccharides (3-10 monosaccharides) polysaccharides (>10 monosaccharides) starch/glycogen, pectines, cellulose, gums Physiologically important sugars: Glucose, Galactose, Fructose, Ribose CARBOHYDRATES CHO FUNCTIONS Energy 50% of dietary energy (polysaccharides) starch/glycogen Structure - connective tissue - plasma membrane Signal transduction - cell communications Gastro-intestinal health CARBOHYDRATES Simple SUGARS CHEMISTRY Complex STARCHES GLUCOSE ENERGY (1 g – 4 Kcal) + GLYCOGEN (glucose storage) Liver Skeletal muscle Heart Kidneys + FAT (excess glucose) CARBOHYDRATES DIETARY CHO w Grains, millet, roots, tubers - polysaccharides – starch Breakdown: starch – Maltose - Glucose Inulin (Fructosan) – starch from tubers - hydrolysis to Fructose w Legumes, soy Starch, oligosaccharides (Raffinose, Stachyose) w Beets, fruits, honey, high fructose corn syrup (HFCS) Sucrose = Fructose + Glucose w Dairy Lactose = Glucose + Galactose CARBOHYDRATES SOURCES Simple MONOSACCHARIDE (Hexose) SOURCES D - Glucose (older name “Dextrose”) SIGNIFICANCE Found naturally in few foods (corn syrup), fruit juices }} body “sugar” found in blood and tissue fluids Hydrolysis of maltose, cane sugars, lactose, starches }} cell fuel CARBOHYDRATES SOURCES Simple MONOSACCHARIDE (Hexose) SOURCES D - Fructose Honey, fruits, juices Hydrolysis of Sucrose from cane sugar SIGNIFICANCE }} changed to G in the liver, serves as basic body fuel CARBOHYDRATES SOURCES Simple MONOSACCHARIDE (Hexose) SOURCES D - Galactose Hydrolysis of Lactose (milk sugar) SIGNIFICANCE }} changed to G in the liver, cell fuel, synthesized in mammary gland to make lactose of milk CARBOHYDRATES SOURCES Simple DISACCHARIDE SOURCES Maltose Germinating cereals Malt products by hydrolysis of starch SIGNIFICANCE }} hydrolyzed to D Glucose. Basic body fuel CARBOHYDRATES SOURCES Simple DISACCHARIDE SOURCES Sucrose Cane, beet sugar, maple sugar, molasses, carrots, pineapple SIGNIFICANCE }} Hydrolyzed to G and F, body fuel CARBOHYDRATES SOURCES Simple DISACCHARIDE SOURCES Lactose Milk SIGNIFICANCE }} Hydrolyzed to G and Gal, body fuel, milk production during lactation CARBOHYDRATES SOURCES POLYSACCHARIDES SOURCES Starch Cereals, buckwheat, legumes, cassava, potatoes or other vegetables SIGNIFICANCE }} The storage form for CHOs in plant / Digested – soluble starch – Dextrin, Maltose – Glucose / Undigested – resistant starch – promote health CARBOHYDRATES SOURCES POLYSACCHARIDES SOURCES Dextrin Formed as intermediate products in the breakdown of starch SIGNIFICANCE }} Dextrin – hydrolyzed – Maltose, Glucose CARBOHYDRATES SOURCES POLYSACCHARIDES SOURCES Oligosaccharides Partially digested starch (size 3-10 G molecules) SIGNIFICANCE }} formed naturally through starch digestion Commercially used in special formula for infants, persons with GI problems, sport drinks Stachyose + Raffinose – in legumes (beans, soybeans) }} indigestible PREBIOTICS Fermentation by bacterial flora – Short Chain Fatty Acids, gas, GI tract health CARBOHYDRATES SOURCES POLYSACCHARIDES SOURCES Glycogen Meat SIGNIFICANCE }} The storage form of CHOs in animals CARBOHYDRATES POLYSACCHARIDES Classification (chemical): homo vs. hetero-polysaccharides (mucopolysaccharides) Storage: plant vs. animal Structure: - amylose (plant, linear structure) - amylopectine (plant, branched structure) - glycogen (animal, branched structure) - cellulose (linear, plant, undigested) - hemicelluloses (plant, branched, xylose) - pectin (plant, from fruit and jellies, non absorbable) Hetero-polysaccharide (Mucopolysaccharides) - chondroitin sulfate, heparin, hyalluronic acid CARBOHYDRATES DIGESTION Starch – the major CHO made of Glucose units=homopolysaccharide - linear a-1, 4 glycosidic branch, Amylose; - linear a-1,4 & branched, and a-1,6 glycosidic bonds: Amylopectin Salivary and pancreatic amylase act on interior a-1,4 glycosidic linkages Starch – after partial digestion g limit Dextrin (8-10 C) Limit Dextrin g Maltose + Isomaltose (enzyme: Dextrinase) Isomaltose g 3 Glucose (enzyme Isomaltase) Maltoseg 2 Glucose (Maltase = brush border disaccharidase) Sucrose g Glucose + Fructose (Sucrase = brush border disaccharidase) Lactose g Glucose + Galactose (Lactase = brush border disaccharidase) Isomaltase g the only enzyme that digests a-1,6 glycosidic bonds. CARBOHYDRATES DIGESTION a amylase active after first month following birth Cellulose: b-1,4 Glucose units – No human enzyme can break this bond; Undigested CHOs escape to large intestin Raffinose, Stachyose = Prebiotics Prebiotics = food ingredients - stimulate the growth and/or activity of Bifidobacteria and Lactic bacillus This group of bacteria –beneficial effects on the host Prebiotics = bifidogenic factor Prebiotics = typically are carbohydrates (oligosaccharides) Many forms of dietary fiber (soluble fiber) exhibit prebiotic effect. Health benefits: same with Bifidobacteria and Lactic bacillus : positive effects on Ca and other mineral absorption, immune system effectiveness and strength, bowel pH, -reduction of Inflammatory Bowel Diseases and Colo-rectal Cancer risk ( bifidogenic effect, plus production of SCFA) CARBOHYDRATES DIGESTION Starch – the most important polysaccharide (homopolysaccharide) Glucosan = GLUCAN - eaten after cooking (the heat of cooking gelatinizes the starch granules and increases their susceptibility to enzymatic digestion ( a amylase) Resistant starch – indigestible starch Sources: cereals, potatoes, legumes Gelatinization: heat applied to starch granules suspended in a liquid g the starch granules absorb water and swell. Smaller Amylose molecules diffuse out of the swollen starch granules and form a 3D network which trap additional water. CARBOHYDRATES DIGESTION Resistant starch (RS) - sum of starch and degradation products not absorbed in the small intestine of a healthy person. RS 1- physically enclosed Starch (partially milled grains) RS 2 - ungelatinized crystalline granules (banana, potatoes) RS 3 - retrograde amylose - formed during the cooling of starch gelatinized by moist heating RSs - escape digestion in the small intestine, enter the colon g respect RS-similar to dietary fiber) The end product of the fermentation of RS in colon SCFA (propionic, acetic and butiric acid) C02, H2, methane fermentation (in this CARBOHYDRATES DIETARY FIBERS are all from plant food - polysaccharides - non-polysaccharides, lignin resistant to digestive enzymes Insoluble fiber - cellulose (b-1,4 Glucose, cell-wall) - hemi-cellulose (polymer of pentose & hexose) - lignin (non CHO, woody wall of plants) Soluble fiber - pectin (gel forming, intracellular cement) - gum (viscous, from the seeds of fruits) - mucilage (plant seed, viscous, thickener) SUGARS CARBOHYDRATES Impact on human taste because they are sweet primarily Sucrose, Glucose, Fructose Degree of sweetness: - Sucrose = 100% sweetness (standard) - Glucose = 61-70% - Fructose = 130-180% - Maltose = 43-50% - Lactose 15-45% Functions of sugar in cooking: - provide sweetness, texture, bulk, preservation (by raising the osmotic pressure), fermentation (bread, alcoholic beverages.) Properties of sugar: - browning reaction - reducing sugar - sugar alcohol Non-caloric sweeteners: Saccharin, AceK, Aspartame, Splenda CARBOHYDRATES ABSORBTION - Facilitated transport - use carrier proteins, Glucose Transport Protein GLUT (integral protein), from high to low concentration, with gradient - allows Glucose to enter and exit - Active transport - against gradient, co-transport, ATP required - brush border cells and renal tubule Active transport of - Glucose - Galactose - Co-transport with Na+ - Na+/K+ ATP–ase dependent - GLUT-5 mediated CARBOHYDRATES GLUT TRANSPORTERS Human facilitated - diffusion Glucose transporter family (GLUT1-5) GLUT 1 Km for hexose uptake = 1-2 (red cells) (major expression sites: placenta, brain, kidney, colon) GLUT 2 Km for hexose uptake = 15-20 (hepatocytes) (liver, pancreatic b cell, kidney, small intestine) GLUT 3 Km =10 (brain, testis) GLUT 4 Km = 47 (muscle: skeletal and heart; brown & white fat) GLUT 5 Km = 6-11 (small intestine, specific for Fructose) Km, MICHAELIS- MENTEN constant Km - affinity of a protein for a particular substrate Km - small = high affinity CARBOHYDRATES GLUT TRANSPORTERS GLUT 1 (erythroid – brain carrier) - RBC, heart, kidney, adipose, brain - constituent of blood brain barrier - Km for uptake in RBC less than Km for exit, asymmetric transport - low Km enables uptake when blood Glucose is low (and intracellular demand is high) - Insulin independent in some cells GLUT 2 (liver Glucose transporter) Liver, kidney, small intestine, b-cells of pancreas - low affinity for Glucose, symmetric transport - rapid efflux following gluconeogenesis - useful during absorption of Glucose, Galactose - Insulin independent CARBOHYDRATES GLUT TRANSPORTERS GLUT 3 (brain Glucose transporter) - adult brain, kidney, placenta, spermatozoa - mainly expressed in neurons - low affinity for Glucose, but higher than GLUT 1 - Insulin independent GLUT 4 (Insulin responsive Glucose – transporter) - adipocyte, skeletal and cardiac muscle - increased maximum velocity for Glucose, Insulin dependent GLUT 5 (Fructose transporter) - mainly expressed by jejunum, kidney, skeletal muscle - transports Fructose better than Glucose - High in spermatozoa which uses Fructose as fuel GLUT 6-7 6 similar to 3 7 similar to 2 CARBOHYDRATES GALACTOSE - uses GLUT 2 proteins like Glucose - cleared by the liver rapidly, hence high blood Galactose is not common - most Galactose in the cell is used as structural CHO or connected to Glucose and stored as glycogen - body can convent Glucose to Galactose, hence not essential CARBOHYDRATES FRUCTOSE - Cleared rapidly by liver - Converted to glucose and used in glycolysis or stored as glycogen in a relatively small amount Uses GLUT 5 Larger amount contributes to weight gain, could exacerbate hyperlipidemia or insulin resistance induces protein fructosylation and/or oxidative damage CARBOHYDRATES METABOLIC REGULATION Normal Glucose in blood is 70-105 mg/dl Following a meal it increases and during fasting decreases Tightly regulated, so brain can always access Glucose (140g/day – minimum for brain working properly) Mono-saccharides from digested meal enter liver through portal circulation Glucose phosphorylated by hexokinase/glucokinase CARBOHYDRATES METABOLISM Hexokinase in a fasting state - subject to feed back inhibition - high affinity (low Km) Glucokinase - used in a well fed state - not regulated - has low affinity, high Km, high Vmax Fructose and Galactose converted to Glucose CARBOHYDRATES METABOLISM IN PHYSIOLOGIC STATE Well fed (Insulin released) - 30 -60 min following a meal, blood Glucose increases - size of meal, fiber content, influent this - Glucose uptake, glycolysis, Glycogen synthesis, and lipogenesis increases - muscle and liver Glycogen store replenished - within 2 hours blood Glucose and Insulin levels return to normal CARBOHYDRATES CARBOHYDRATES POST ABSORPTION STATE - Following over night fast or skipping meals - Gluconeogenesis is (+) - liver uses glucogenic amino acids, lactate and glycerol to synthesize Glucose - Brain continues to use Glucose - Liver Glycogen depleted CARBOHYDRATES GLUCOSE METABOLISM CARBOHYDRATES GLUCOSE METABOLISM 1. Glucose transported into cell 2. Conversion of Glucose into Glycogen Pancreas releases Insulin hBlood glucose Glucose – how CHOs circulate in the blood stream Normal Blood Glucose = 100 mg / dl (70-105 mg/dl) 1. Breakdown of Glycogen to Glucose 2. Increased synthesis of Glucose Pancreas releases Glucagon iBlood Glucose CARBOHYDRATES STARVATION - Available Glucose spared for brain and RBC - Glycogen breakdown 4-24 hours following fast - Gluconeogenesis starts 8-40 hrs following fast - Ketone synthesis occurs after 1-2 days and becomes an important fuel source CARBOHYDRATES BLOOD GLUCOSE LEVEL, HORMONES & TIME CARBOHYDRATES CHARACTERISTICS Simple SUGARS UNREFINED REFINED ABSORPTION Complex STARCHES UNREFINED REFINED longer quickly longer quickly VOLUME EATEN large small large small ENERGY DENSITY small large small large INSULIN RELEASE BLOOD SUGAR LEVEL (Calorie/ Volume) CARBOHYDRATES GLUCOSE METABOLISM DIETARY GLUCOSE hBLOOD GLUCOSE h GLYCOGENOLYSIS h GLUCONEOGENESIS h INSULIN h LIPOLYSIS h FFA h GLYCEROL i OXIDATION h G OXIDATION hLIPOGENESIS, g FFA h GLYCOGEN SYNTHESIS i INSULIN h SOMATOSTATIN h GLUCAGON ( GLUCONEOGENESIS iBLOOD GLUCOSE CARBOHYDRATES GLUCOSE METABOLISM Food intake & energy expenditure are under - long term signals (Insulin, Leptin, Ghrelin) - short term signal (Colecystokinine) Insulin (I) secreted by pancreatic b-cells Stimuli : - Glucose and Amino Acids circulating in the blood - Incretin hormons: - Glucose dependent insulino-tropic polypeptide (GIP) - Glucagon-Like Peptide 1 (GLP-1) Insulin indirectly stimulates Leptin production Leptin – secreted by adipose cells Insulin and Leptin act on CNS and (-) Food intake (+) energy expenditure Ghrelin - secreted by stomach endocrine cells, (+) food intake (-) fat oxidation -normally suppressed after meals CARBOHYDRATES FRUCTOSE METABOLISM – HEALTH IMPACT Differences in hepatic metabolism of Glucose and Fructose - Fructose more lipogenic than Glucose: TG levels increase postprandial, effect more pronounced in persons with existing hyperlipidemia or Insulin resistance - Fructose does not stimulate Insulin secretion It results in decreased level of circulating Leptin Fructose does not suppress Ghrelin secretion after meal Chronic consumption of a diet high in Fructose (sugar, high fructose corn syrup) associated with dietary fat and inactivity involved in increasing energy intake, weight gain and obesity CARBOHYDRATES RECOMMENDATIONS Glucose intake: Infants 0-6 months AI= 60 g/day 7-12 months AI=95 g/day Children <18 years AI=130 g/day Adults at least AI=140 g/day in order to provide adequate CHO for brain, CNS ; need not to depend on ketones or TAG Recommendation = 45-65% energy coming from CHO CARBOHYDRATES DAILY AMOUNT Calories per day CARBOHYDRATES 60% PROTEINS 15% FATS 25% Glucose equivalents: 100 g whole wheat bread 100 g potatoes- cooked 100 g banana 100 g grapes 100 g fruit 100 g vegetables 100 g table sugar 100 g honey Example: A person of 150 lb (70 kg) Needs 1,260 Calories from glucose 1,260 /4 = 315 grams glucose/day 50 g glucose 20 g glucose 20 g glucose 20 g glucose 5-10 g glucose </=5 g glucose 100 g glucose 100 g fructose CARBOHYDRATES RIGHT DECISION Eat more! 100 g wheat bread 100 g potatoes- cooked 100 g banana 100 g grapes 100 g fruit 100 g vegetables 50 g Glucose 20 g Glucose 20 g Glucose 20 g Glucose 5-10 g Glucose </=5 g Glucose Eat less! 100 g table sugar 100 g honey 100 g Glucose 100 g Fructose CARBOHYDRATES 90 g l u c o s e 85 80 P l a s m a l e v e l GLYCEMIC INDEX (how G rises after a meal) 65 Depends on: - type of CHOs, cooking methods, commercial food processing 75 Apple 70 Apple Sauce Apple Juice 60 55 30 60 M i n u t e s 90 a f t e r 120 m e a l 150 180 CARBOHYDRATES RIGHT DECISION Glycemic Index (GI) (rate at which Glucose is absorbed and delivered to the blood) Low GI - Low rate = constant blood Glucose level after meal - Best food has low GI Examples: brown rice, barley, whole wheat bread, legumes High GI - Increased blood Glucose, increased Insulin delivery to the blood, decreased blood Glucose shortly after the meal Examples: white bread, potatoes, juices, processed foods: smaller particles (potatoes) CARBOHYDRATES COMPARISON 8 apples = 4 ounce chocolate, 1 ounce= 28 g 25 med carrots = 1 can soft drink 1 can = 240 ml CARBOHYDRATES A variety of plant – based foods help prevent wide fluctuation in blood glucose levels REFERENCES Modern Nutrition in Health and Disease, 10 th. Ed www. Pubmed.com http:// cme.medscape.com QUESTIONS? QUESTIONS? QUESTIONS? QUESTIONS? QUESTIONS? QUESTIONS? QUESTIONS? QUESTIONS? QUESTIONS? QUESTIONS? QUESTIONS?
