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McMaster University
Danny M.Pincivero

89 LECTURE - CARBOHYDRATES Figure H4-1: Macronutrients available per capita over time WHAT IS A CARBOHYDRATE? • Is a “hydrate of carbon” • Manufactured by plants Ex: making a glucose molecule - Soluble fibre gives a fullness sensation b/c of gel form - Absorbs fatty acids within the digestive system and make those fatty acids less bioavailable and can’t be absorbed so the ability to absorb cholesterol will decrease as well so reduces cardiovasc disease? - Insoluble fibre speeds up gastric motility.. helps absorb water from digestive system into cardiovasc which , decreases absorption time, decrease chance of type 2 diabetes - Too much insoluble fiber in diet reduces the time for absorption since motility is so fsat that it can lead to nutritional deficiencies KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 90 Storage form of glucose • Animals: glycogen – resides in skeletal muscle • Plants: starch (amylopectin and amylose) & fibre • Liver cells store glucose as glycogen in a very dense form • Amylose – 25% of starch that we find in plant based foods • Amylopectin – glucose molecules are bound in a linear array but every 25-30 molecules there is a branch point where additional glucose moleules can be formed , glycogen branches are every 8-12 molecules so it’s more effective at packing in FIBRE Non-digestible carbohydrates (in plants) - Dietary fibre  naturally occurring fibre, can’t break it down into individual glucose units – don’t get the glucose absorbed into the cardiovasc system, reduces carbohydrate bioavailability - Functional fibre: refers to “added” fibre to food, occurs during manufacturing and food processing periods , could be natural or synthetic KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 91 Function of carbohydrates? 1) “Burned” for energy (glycolysis), cells in body constantly need to make ATP for survival – only make ATP if we provide fuel to do that, RBCs and brain neurons preferentially use glucose as an energy substrate to make their ATP 2) Ribose and deoxyribose sugars: RNA & DNA incorporate carbs as their backbone 3) Structure and strength of plants 4) Linked to proteins and lipids Glycoprotein: Covalent link between protein and a carbohydrate monomer… found on cell surfaces - Cell-cell adhesion Glycolipid: Forms myelin around neuron axons – myelin is an insulator, doesn’t allow charges to escape, speeds up conduction – carbs are important for forming glycolipids KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 92 FORMS OF CARBOHYDRATES Monosaccharides: simples form of CHO Contains 3 to 9 carbon atoms Smallest (3 carbons)……called a TRIOSE Examples: Dihydroxyacetone (ketose) and glyceraldehyde (aldose) • Important energy intermediates!….glycolysis and FA. Monosaccharides •Tetrose - 4 C •Pentose - 5 C •Hexose - 6 C •Heptose - 7 C Sugar alcohols • Derived from monosaccharides 3-9 carbon atoms • Used as a sweetener (sorbitol made from glucose)….sweetens “sugarless” gum Sugar alcohols contain very few calories as opposed to fructose used to sweeten KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 93 CHO DIGESTION KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 94 - Amylase is a protein enzyme – low pH, it gets denatured , small intestine and pancreas play bigger role in secreting enzymes – breakdown of disaccharides – lactase, maltase, surcrase - liver cells have a metabolic need – glucose supplies liver cells with energy, they take in monosaccharides and use it for their own energy Disaccharides: sucrose, lactose, maltose Oligosaccharides: 3-9 CHO monomers • Considered to be a complex carbohydrate Examples: 1) Raffinose: galactose, glucose, and fructose 2) Stachyose: 2 galactose, glucose, fructose • Found in dry beans, peas, lentils • Fermentation: (fiber breakdown) anaerobic breakdown of CHO by bacteria; SI is major absorptive organ, when chime reaches LI, gone psat the point of potential absorption POLYSACCHARIDES KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 95 Dietary form: starch • Vegetables and fruits • Grains: wheat, corn, oats, barley, rice • Legumes: peas, beans, lentils, soy • Tubers: potatoes, yams, cassava (toxic in raw form) EXAMPLES OF NUTRIENT VALUES OF PLANT-BASED FOOD: ITEM Energy Protein CHO (g) Fat (g) Fibre (g) (kcal) (g) 1. Iceberg lettuce (1 cup) – 55 7 1 1 <1 1 grams 2. Baked potato with skin (0.5 cup) – 57 1 13 <1 1 61 grams 3. Medium sized fresh tomato – 123 26 1 6 <1 1 grams 4. Medium sized apple with skin – 81 <1 21 <1 4 138 grams 5. Watermelon (1 cup) – 152 grams 49 1 11 1 1 LETTUCE (iceberg vs. leaf lettuce) – 1 cup Iceberg lettuce (55 grams) Leaf lettuce (56 grams) Energy (kcal) 7 10 Protein (g) 1 1 CHO (g) 1 2 Fibre (g) 1 1 Vitamin A (RE) 18 106 Folate (microgram) 31 28 Vitamin C (mg) 2 10 KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 96 Calcium (mg) 10 38 Iron (mg) 0.3 0.8 QUESTIONS: 1) Which one is “better” for you?……definitely, ____leaf lettuce___________________ 2) Which one is more expensive?…..depends on in-store specials of the week. Nutrient density – amt of energy per unit So what’s the main point? Chemical structure determines mono-, and disaccharides, but………not all CHO are the same. (this is a well-recognized term in the food/diet industry as “good carbs” and “bad carbs”). - Once we move to more compex carbs – clearly see not all carbs are the same, contrast carbs and fiber – still made of fiber units but will have diff effects on physiology SO, WHY DO WE NEED TO EAT CARBOHYDRATES? 1) ENERGY needs • Fuel source for neurons (only uses glucose except during starvation….can uptake protein. • Red blood cells only use glucose. • Need CHO to metabolize other fuels……”Fat burns in a flame of carbohydrates” • To metabolize fat, we have to simultaneous metabolize carbs – carbs not stored in abundance unlike fat?? • Glucose is the preferred unit, however during periods of starvation when carb supply is low, neurons don’t care – want energy, unique in that they can take up amino acids and use those maino acids for energy and convert them to enter krebs cycle and a ton of electrons  mitochondria can make ATP red blood cells only use glucose • Low carb diet low energy diet – skeletal muscle provides the amino acids, breakdown of muscle protein to make new glucose and liver cells do that • Liver can turn amino acids into glucose – they get amino acids from skeletal muscle protein KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 97 I norder to break down fatty aicds, glucose must be broken down at the same time KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 98 Ketone bodies • Major source of production is the liver (inside mitochondrion) • Heart and renal cortex cells: ketone bodies are used as fuel. • Accumulate as a byproduct of fat and protein metabolism Starvation and diabetes: • Brain neurons use ketone bodies (water soluble)…… …..converted to Acetyl CoA • Accumulation from / byproduct of both fat and protein metabolism • Diabetes mellitus – type 1 – ketone body accumulation is a problem – potential fatal acutely if a person goes into severe ketoacidosis – reduce pH of fluids in which they reside – ketone bodies get out into blood and tissues and reduce pH making them acidic • Type 1 DM  cells in pancreas do not produce insulin (no insulin production) • Insulin is a hormone that promotes storage meaning the macronutrients move from the cardiovascular system into cells , acts on glucose, regulates blood glucose levels, promotes fats storage by minimizing fat breakdown • In order to burn fat for energy, triglycerides have to be broken down in fat cells; when insulin is not available, fat breakdown is unregulated – people with type 1 DM are often underweight since burning up fat is unregulated; insulin prevents fat breakdown • If dietary energy is low esp from carbs, body will shift towards utilizing stored amino acids in muscle tissue to help generate ketone bodies to provide energy to neurons to convert them to acetyl coA which is the entry pathway into the kreb cycle which gets started and cells can make ATP to serve metabolic needs • High levels of ketone bodies in blood reduces adipocyte lipolysis (breakdown of stored fat), accumulation shuts down fat breakdown however type 1 DM natural production of insulin is non existent which overrides negative feedback loop • Carbs are readily available can be imported easily requires less chem reactions to get through them and break them down KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 99 SO, WHY DO WE NEED TO EAT CARBOHYDRATES? (cont’d) 2) Pregnancy: fetus and placenta “feed” on glucose Gestational diabetes: elevated blood glucose during pregnancy, reversible, body’s inability to regulate blood glucose, <10% of pregnant women develop this. Condition is eliminated following birth. 3) Spares muscle protein degradation for energy Glucose must be synthesized from muscle protein (amino acids have to be broken down) Amino acids converted to: (1) ketone bodies, (2) fatty acids, (3) glucose Ketone bodies – when carb levels are low which leads to an increase in protein metabolism Fatty acids – when dietary energy in carbs are sufficient, amino acids can be turned to fatty aicids – not preferred or easy Glucose – by liver cells Extra amino acids can be converted to fatty acids in the event that dietary energy is abundant with carbs (glucogenic – amino acid that can be converted to glucose) CARBOHYDRATES AND ENERGY How much glucose do we carry in our bodies? Concentration (mmol/kg ww) Energy (kJ/body) Muscle glycogen 80-100 6400-8000 Liver glycogen 300-500 1550-2600 Plasma glucose 5 mM 50 Tap into liver glycogen when muscle glycogen levels are low – when dietary intake is insufficient and during long term exercise eg .marathons Overall glucose content Blood glucose: 30 g Liver glycogen: 90 g KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 100 Muscle glycogen: 350 g Breakdown glucose : pyruvate portion in cytoplasm .. breakdown fatty acid gets imported to muscle cell outer surface of mitochondrion ….??????????????????// KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 101 CARBOHYDRATES AND ENERGY (cont’d) ATP yield for CHO and fats • 5.1 kcal/L of 2 (carbohydrates) • 4.8 kcal/L of 2 (fats) • Due to substrate level phosphorylation (direct production of ATP when glucose undergoes conversion , acetyl coA generated electrons .. is indirect, glycolysis makes 4 gross ATP.. don’t get anaerobic result when metabolizing fats because it requires O2) Glucose  pyruvate  acetyl coA  mitochondrion, bit more because of anaerobic component fatty acid  muscle cell ripped off 2C at a time into acety coA Get more energy out of carbs b/c of substrate level phosphorylation Minimum intake of CHO: 130 g/day for nervous system function 1 cup of dates = 131 g 1 mango = 35 g 1 soft pretzel = 84 g KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 102 - Cells in pancreas have the ability to bind glucose to the surface called beta cells which initiate a metabolic cascade inside the cell and beta cells secrete a hormone protein called insulin into cardiovascular system - Increase in insulin when you eat, general response of insulin is macronutrient storage - Glucagon will stimulate glycogenolysis in the liver if glucose levels drop too low to breakdown glycogen to beak glucose molecules off and individual units will enter the CV system , increases blood glucose levels Glycemic index (GI) • Is a measure (no units) of the potential of food to raise blood glucose levels. • 2 different standards: one slice of white bread or pure glucose (both taken as 100%) • Doesn’t indicate the amount of carbs, it’s reflective of how fast our bodies can break it down and absorb it Factors affecting the glycemic index of foods: 1) Proportion of CHO content of the ingested food • Increased %CHO, increased G.I. Examples (compared to pure glucose ingestion) Ice cream = 61 Baked potato = 85 Instant rice = 91 KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 103 - glycemic index indicates the chances of that food raising blood glucose levels quickly - High glycemic index high if its >= 70 - low glycemic index is <= 55 - fat in ice cream prevents quick absorption of glucose - french fries have a lower glycemic index than baked potato because of the extra fat content of food preparation in French fries which inhibits absorption 2) Type of carbohydrate Simple versus complex Complex carbs requires more enzyme action – more steps – more time – slower Role in fat storage.. insulin action High glycemic index food – bad carbs? Does it matter? The faster blood glucose goes up, the more insulin is released, insulin promotes fat storage Type !! – muscle cells don’t recognize insulin, they’re insulin-resistant Factors affecting the glycemic index of foods: (cont’d) 3) Cooking Heat helps to disrupt chemical bonds – faster digestion Example: Pasta GI (5 min boiled) = 34 Pasts GI (10 min boiled) =40 Putting pasta in boiling water – adding energy (heat), molecules don’t have ability to absorb energy so they break down Glycemic Load - glycemic index multipled by the amount of available carbohydrates in a food source /100 KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 104 - predictor of developing Type !! diabetes mellitus and cardiovascular disease - example: 1) corn muffin: GI = 102 (compared to glucose), 29 g carbs/serving, GL = 30 2) bran muffin: GI = 60 (compared to glucose), 24 g carbs/serving, GL = 15 Blood glucose response to feeding – GL reflected in total change of BG[ ] KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 89 KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 89 DIAGRAM – GLUCOSE ABSORPTION INTO MUSCLES - Skeletal muscle is location of most stored glucose as glycogen (more muscle tissue than liver cells) - GLUT = glucose transporter; protein grey purple things rep alpha helices , has th alpha helices within the membrane and outside are the amino acids (45 amino acid in sequence from amino end – asparagine 45 ) - GLUT 1 gets glucose out of cardiovasc into muscle tissue, Provide muscle tissue with important substrate to breakdown for energy and storage of carbs… - GLUT 1 is permanently embedded into the membrane of muscle cells, functions to pick a glucose molecule to bind to amino acid and when it binds the protein inverts that glucose molecule to the interior of the cell depending on the energetic needs of the cell the glucose molecule will move through glycolysis or glycogen synthesis - GLUT 1 transports glucose inside the cell and depending on energetic state, if energetic state is high (high demand of ATP) and need is high this glucose will be used for glycolysis - Massive influx of glucose molecules after a meal which stimulates pancreas to release insulin which binds to another protein on the membrane of muscle cells - Major function of insulin is to increase the uptake of glucose, decrease blood glucose levels - Insulin has to be released from pancreas for this to work, Type ! DM, pancreas can’t secrete insulin - Insulin affects the vesicle containing GLUT4 (same basic transporter/protein as GLUT1) - Diff btwn glut 1 and glu4 is that glut1 is permanently embedded, glut 4 exists in the cytoplasm - Glut 4 is useless since its job is to take extracellular glucose into the cell but its trapped in the vesicle in the cytoplasm it doesn’t do much unless we get vesicle to the membrane – action of insulin when it binds to the recetpr to activate a series of enzymes which causes translocation o Causes vesicle to fuse on the inside of the cytoplasm on the membrane which takes the glut4 and embeds it temporarily into the membrane (7-10 minutes) before cell reabsorbs it and repackages it into a vesicle o Recruits additional help to move a lot of glucose molecules, into the cell eg after a meal  glut 1 isnt enough so glut 4 recruits help from glut 4 by moving it to the membrane KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 90 - Type 2 DM lose ability from membrane down, cells don’t recognize insulin – have more than the avg concentration of insulin since the body’s response is to produce more insulin to decrease blood glucose concentration - Skeletal muscle in people with Type 2 DM lose ability from muscle down but if those same muscle fibers are electrically stimulated (they contract), the restoration of this normal process is very quick – shows that exercise is a very effective mechanism for regulating blood glucose levels – activating muscle fibers, nervous system recruitment, cells producing force will accomplish moving glut 4 PANCREATIC HORMONES Insulin • Produced by beta cells of the pancreas • Helps cells take in glucose from the blood • Stimulates the liver to take up glucose and convert it to glycogen • Overall effect of lowing blood glucose • 51 amino acid sequence, with 2 chains (A and B) • Disulfide brides between cysteine residues • Promotes fatty acid storage and amino acid storage Glucagon • Produced by alpha cells of the pancreas • 29 amino acid polypeptide • Signals a physiologically starved state • Stimulates the breakdown of glycogen to glucose • More glucose is available to cells of the body KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 91 • Stimulates gluconeogenesis – the production of glucose from amino acids • Overall effect of raising blood glucose • When blood glucose levels are low – signal for al • • pha cells to secrete glucagon • Target liver cells to reelease glucose units into cardiovasc system - Glycolysis starts when we have a glucose molecule and we run through complicated chemical pathway, glycogenolysis is breakdown of muscle glycogen and occurs in muscle cells as a result of glucagon to get glucose to cells that need it MIDTERM STOPS HERE CHO RELATED DISORDERS Diabetes mellitus “A disorder of carbohydrate metabolism, characterized by hyperglycemia (higher than normal blood glucose levels) and glycosuria (presence of greater than normal amount of glucose in the urine) and resulting from in adequate production or utilization of insulin” Tabers Cyclopedic Medical Dictionary • 2 million Canadians affected • 10% Type I diabetes (IDDM) (insulin dependent diabetes mellitus, dependent on some external/ exogenous source of insulin since they’ can’t produce it ) • 90% Type II diabetes (NIDDM) (non-insulin dependent DM, insulin is produced but cells don’t respond to the insulin, in more severe cases – insulin can be prescribed) KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 92 Gestational diabetes  3.7% of all pregnancies  8-18% of all pregnancies among Aboriginal women  Problem is resolved soon after birth  Women who do develop it have a greater risk of developing type II later on Diabetes  Greek derivative., “passing through”  A general term for diseases characterized by excessive urination Mellitus  Latin, “sweetened with honey”  Presence of sugar in the urine (glycosuria) Diabetes insipidus  Impaired water re-absorption in kidney (lack of ADH – hormone produced by posterior pituitary.. antidiaretic, stimulates kidneys to reabsorb water back into cardiovasc system)  Kidneys main function is to clean out blood, remove toxins etc and to help maintain plasma volume (certain amt of blood in cardiovasc system) – does so by initially filtering blood then reabsorbing many of those filtration products, one being water KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 93 TYPE I DIABETES MELLITUS  Auto-immune disorder (individual’s immune system is attacking their own cells, in many cases a virus can signal body to attack beta cells – no longer recoverable once ingested, and can no longer make insulin )  Beta-cell ingestion by the immune system 1) No production of insulin 2) Leads to hyperglycemia (abnormally high blood glucose) Normal range = 80-110 mg/dL (4.4-6.1 mmol/L) Meal: may rise to 140 mg/dL - Without insulin (which activates more glucose transporters), there’s no signal to bring glut4 to the membrane which leads to this hyperglycemic state - Litte bit of glucose uptake into the cells due to glut1 transporters (permanently embedded) 3) No insulin, no uptake of glucose into cells Consequences?? Muscle: No translocation of GLUT4 Liver: GLUT2 (same protein structure) not activated (insulin is an activator of GLUT2, embedded in liver cells, so without activation GLUT2 isn’t used) So what does the liver “see”? Glucose is not brought in.. (liver stores glucose very efficiently) therefore low blood glucose, blood glucose levels are high but body organs think its low since glucose transporters haven’t been activated  liver increases the rate of glycogenolysis (already storing glucose in the form of glycogen, takes glucose off liver glycogen so glucose units can get into cardiovasc system and circulate to tissues that have metabolic need for it.. makes hyperglycemia worse) Direct effect of hyperglycemia  high blood pressure KIN 1F03 – Human Nutrition in Exercise and Health D.M. Pincivero, 2012 94 So now what happens? Liver increases rate of glycogenolysis….makes hyperglycemia worse. High blood pressure leads to kidney problems High blood pressure adds more force to the inside of blood vessels; if you add more solutes, have to dissolve more substances into blood, more pressure on vessel walls  increased blood pressure  blood vessel rupture esp in kidney  kidney problems. 3) No insulin, no uptake of glucose into cells Consequences?? Renal threshold: ≈170-200 mg/dL (upper level that maximizes the amount of glucose that is recovered from the kidney.. kidneys main function is to filter.. reabsorbing items from filtrate is a key function) Blood glucose level in which glucose is not reabsorbed from the kidneys……glycosuria (glucose in the urine). Max capcity that we can reclaim glucose because of hyperglycemia, upper level is reached so glycosuria results – can’t reabsorb all glucose molecules initially filtered out so filtrate becomes urine so there’s an increase in amount of glucose in urine Exceeds the capacity of renal tubules for re-absorption urinary glucose will attract water molecules glucose molecules stay filtered out of blood but hold on to water molecules that were filtered out as well.. so we see increase in glucose and b/c of extra molecules that glucose s holding on to, we see e
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