Dr. Greene Week 4 Notes
Dr. Greene Week 4 Notes NTRI 2000-002
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This 5 page Class Notes was uploaded by Rachel Ferrell on Sunday February 14, 2016. The Class Notes belongs to NTRI 2000-002 at Auburn University taught by Michael Winand Greene in Fall 2015. Since its upload, it has received 51 views. For similar materials see Nutrition and Health in Nutrition and Food Sciences at Auburn University.
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Date Created: 02/14/16
Rachel Ferrell NTRI 2000 2/8/16 Chapter 4: Carbohydrates: Carbs Basics: • Main fuel source for body o Brain, nerve cells, Red blood cells, exercising muscles o Also is for all cells • Form of carb in the blood→glucose o Glycogen= a form of glucose that is stored in the liver • Ultimate source of carbs?→sun through photosynthesis Carbon Cycle in Animals: • Metabolism= C (H n) 2 + n O →e2ergy +CO +H2O 2 • Simple carbs = sugars o Monosaccharide o Disaccharides • Complex Carbs=starches, fiber Simple Carbs: • Monosaccharide o Basic unit for all carb structure o Glucose(dextrose) § Major monosaccharide found in the body § Found in blood→blood sugar § Derived mainly from digestion of starches and disaccharides § Spares body proteins § Maintains acid-‐base balance § Prevents ketosis= buildup of ketones in blood from fat breakdown o Fructose § Converted to glucose and other compounds § Also called “fruit-‐sugar” § One dietary source is high-‐fructose corn syrup • In soft drinks→55% fructose and 45% glucose § Metabolism of fructose and glucose is different o Galactose § Part of disaccharide lactose (milk sugar) • Disaccharide o Chemical bonding of two monosaccharides o Maltose= glucose+glucose o Sucrose=glucose+fructose o Lactose=glucose+galactose Complex Carbs: • =polysaccharides or starch • may contain 1000 or more glucose units • storage form of glucose • found in grains, vegetables, fruits • food labels→ “other carbs”=starch content • starches found in plants o digestible o Amylose= 20% of digestible starch found in plants; long straight strand of glucose molecules o Amylopectin= 80% of digestible starch found in plants; highly branches chain of glucose molecules o Enzymes break down these starches at its ends • Starch stored in humans o Glycogen § Identified in 1858 § Structure=highly branched; therefore quick energy access § About 1800 kcal stored in body presently § Major storage sites: • Muscle→1400 kcal stored o Can be depleted→muscle fatigue • Liver→400 kcal stored o Can be depleted but takes longer (18 hrs) • Fat and Brain→only little stored here; not as accessible source of energy Carb Availability: • Cooking o Softens fibrous parts of plants o Starch granules swell with water→easier to digest • Mouth o Salivary Amylase=starts digestion of starch in mouth; but not much • Stomach o Acid inactivated amylase o No further starch digestion • Small intestine o Alkaline environment promotes starch digestion o Enzymes: § Pancreatic Amylase=breaks starches into disaccharides and trisaccharides § Maltase, Sucrase,Lactase, Dextrinase • Located in the brush border of cells that line the inside of the small intestine • All of these enzymes→substrate specific Lactose Intolerance: • Caused by a decrease in lactase production o Lactase high in infants o Reduced in adults o If not decreased→lactase persistence • Often develops early in childhood • Symptoms: stomach issues • How much consumed is key o Milk=nutrient dense; but must be balanced depending on needs Carb Absorption: • Monosaccharide→absorbed in intestinal cells o Transporter proteins • Absorbed by capillary→liver through portal vein • Liver→fructose and galactose convert to glucose • Glucose→ blood or stored as glycogen or converted into fat Rachel Ferrell NRTI 2000 2/10/16 Blood Glucose Concentration: • How does the body regulate blood glucose levels? o Primary control→liver and pancreas o Secondary control→brain, muscle, adrenal glands • Pancreas o High blood glucose→releases insulin into blood o Low blood glucose→releases glucagon into blood • Discovery of Insulin (1921) o Experiment 1: § Removed pancreas from a dog→ its blood glucose went up § Over urination § Weak until death § Developed diabetes o Experiment 2: § Removed pancreas from dog→then dissected pancreas in lab § Extract from pancreas injected into dog→reversed diabetes Functions of Insulin: • Net effect→lowers blood glucose levels • How? o 1) Promotes glycogen synthesis in muscle, liver, and fat o 2) Increases glucose uptake by the cells in muscle and fat (to take it out of bloodstream) o 3) Reduces gluconeogenesis=process by which glucose is made § in liver and kidney Glucagon Action in the Liver: • Opposite effects of insulin o 1) Causes liver to breakdown glycogen back to glucose § releases it back into the blood→glycogenolysis o 2) Causes liver to synthesize glucose from non-‐carb precursors (gluconeogenesis) § things like amino-‐acids Blood Glucose-‐Adrenal Glands: • located on kidneys • releases epinephrine= responsible for flight or flight response in times of stress o causes quick conversion of glycogen to glucose in the liver Improper Regulation of Blood Glucose: • Hyperglycemia= high blood glucose o Diabetes→Type ½ and gestational • Hypoglycemia= low blood glucose o Reactive hypoglycemia and fasting hypoglycemia • Type 1 Diabetes o Often begins in late childhood o Associated with decreased release of insulin from pancreas o Immune system disorder→destruction of insulin producing cells (thinks they are foreign cells) o Treated primarily by insulin therapy • Type 2 Diabetes o Most common→90-‐95% of all cases § Effects 9% of U.S. population o Associated with obesity o Can also have a genetic component o Pre-‐Diabetes= body becomes more resistant to effects of insulin; therefore, pancreas makes more insulin § Then, pancreas suddenly makes little to no insulin→hyperglycemia How do we Assess Glucose Clearance?: • Oral Glucose Tolerance Test o Drink a high glucose drink and measure blood glucose levels o >140mg/dL and <200mg/dL→pre-‐diabetes • Fasting Plasma Glucose o Fasting instead of drinking more glucose; levels will be lower o >100mg/dL and <126mg/dL→pre-‐diabetes Diabetes Outcomes: • increase risk of o cardiovascular disease o stroke o kidney disease o cancer • possible complications o adult blindness, lower limb amputation Diabetes Treatment: • if cause is obesity→lose weight • in general o diet, exercise, take medications o insulin therapy o bariatric surgery=stomach reduction surgery Carbohydrate Need • recommendations vary widely • RDA→130 grams/day for adults • Food and Nutrition Board: 45-‐65% of calories Carbs in Food Groups: • High carb content o Grains→15 g/serving o Fruits→18g/serving o Milk→12 g/serving • Low carb content o Nuts→ 4 g/serving o Meat and Eggs→ 0 g/serving (eggs < 1 gram) o Vegetables→ 5 g/serving • Are all carbs the same? o After eating 50 grams what happens to you blood glucose when eating beans vs. potatoes? Mashed potatoes makes blood glucose go up more • Glycemic Index o =ratio of the blood glucose response to a given food compared to a standard (used to be a piece of white bread, now it’s straight glucose o based on 50 grams of carbs o Influenced by § Starch structure § Fiber content § Food processing and physical structure § Other macronutrients in food • Glycemic Load o =glycemic index times amount of carbs in a serving divided by 100 o can better predict blood glucose response o not as commonly used as glycemic index • Problems with High Glycemic Index/Load foods o Very high glucose levels o Chronically increased insulin levels o Lead to high blood triglyceride levels, increased fat production o A more rapid return of hunger after a meal, increased tendency for blood to clot o Opposite of this would be consuming protein • Sweeteners o Nutritive sweeteners § Sugar, high fructose corn syrup, honey § Sugar alcohol→ sorbitol, xylitol • Approx. 2.6 kcal/gram • Slow metabolism to glucose § High Fructose corn syrup • Made from corn • 55% fructose and 45% glucose • cornstarch mixed with acid and enzymes • starch is broken down to glucose • some glucose is converted to fructose • improved shelf-‐stability and food properties • Average American consumes 60lbs a year o Alternative Sweeteners § Yield no calories § Ex. Saccharin→Sweet ‘n low, Aspartame→Equal; Sucralose→Splenda § Are there safety issues? § GRAS-‐ generally regarded as safe • Extensive scientific research has demonstrated the safety of the 5 low-‐calorie sweeteners currently approved for use in foods in the United States § But… • Other concerns § Aspartame (Equal, NutraSweet) • Complaints of sensitivity • Headaches, dizziness, seizures, nausea, etc. • Acceptable daily intake : 50 mg per kg body weight (FDA) (approx. 14 cans of diet soda for average adult per day) • Warning label for Phenylketonuria (PKU) § Why do consumers choose products with artificial sweeteners? § Surprisingly • Consumption of artificial sweeteners is not associated with weight loss • Why?
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