Chapter 4: Carbohydrates
Chapter 4: Carbohydrates NTRI 2000-002
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This 6 page Class Notes was uploaded by Kaylen Taylor on Thursday March 3, 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 66 views. For similar materials see Nutrition and Health in Nutrition and Food Sciences at Auburn University.
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Date Created: 03/03/16
Chapter 4: Carbohydrates Monday, February 8, 2016 10:59 AM Carbohydrates o Main fuel source for: Brain Nerve cells Red blood cells (glucose) Exercising muscle o Form of Carbohydrates: Blood glucose Glycogen o Ultimate Source for Carbohydrates Sun o Carbon Cycle in Animals Metabolism: CHO + O 2→ CO 2 H O2+ Energy Simple Carbohydrates Simple Sugars Monosaccharides : The basic unit for carbohydrate structure Glucose (Dextrose): The major monosaccharide found in the body. Also called the "blood sugar" Derived mainly from the digestion of starches and disaccharides. Using glucose spares body proteins. Helps maintain Acid-Base balance. Prevents ketosis Buildup of ketone bodies in blood from fat breakdown. Fructose: Converted to glucose and other compounds. Also known as the "fruit sugar." A bit sweeter than glucose One dietary source is high-fructose corn syrup In soft drinks, 55% fructose and 45% glucose Fructose metabolism is different from glucose. Galactose : Part of a disaccharide known as lactose. Disaccharides: Chemical bonding of two monosaccharides. Maltose: Glucose-Glucose Sucrose: Glucose-Fructose Lactose: Glucose-Galactose Complex Carbohydrates o Starches and fiber o Called polysaccharides or starch o May contain 1000 or more glucose units o Found in grains, veggies, and fruits o Food labels -"Other Carbohydrates" refers to starch content. Starches found in Plants o Digestible by humans Amylose (20%) Amylopectin (80%) o Enzymes break down starch at its ends. o Starches Stored in Humans: Glycogen: Identified in 1858 Highly branched, resulting in quick energy. 1800 kcal present in humans Major Storage Sites: Muscle 1400 kcal stored, but can be depleted (Muscle fatigue) Liver 400 kcal, can be depleted in 18 hours. Also stored in the fat and brain. Carbohydrate Availability o Cooking Softens fibrous parts of plants Starch granules swell with water making it easier to digest. o Mouth Salivary amylase: helps start digestive process o Stomach Stomach acid deactivates amylase, which means no further starch digestion. o Small intestine Alkaline environment promotes carbohydrate digestion Enzymes: Suffix "-ase" is used in biochemistry for enzymes. Pancreatic amylase Breaks starches into disaccharides and trisaccharides. Maltase, Sucrase, Lactase, Dextranase (Disaccharides) Located in the brush border of the cells that line the inside of the small intestine. Each enzyme is very specific o Lactose Intolerance Caused by a decrease in lactase production Lactase is high in infants Reduced in adults If not reduced: lactase persistence, due to a mutation Often develops early in childhood. Symptoms: Abdominal pain Gas Cramps Diarrhea after consuming an amount of lactose How much lactose is consumed is key Milk is nutrient dense Carbohydrate Absorption o Monosaccharides are absorbed through intestinal cells Transporter proteins bring sugar into the cells o Absorbed by capillaries to make it to the liver Via the portal vein o In the liver, fructose and galactose are converted into glucose Glucose is stored as glycogen or fat or passed on into the blood Liver is a major producer of glucose Blood Glucose Concentrations o Primary control of blood glucose is in the liver and pancreas o Secondary Control: Brain Muscle Adrenal glands (on top of the kidneys) o Pancreas: High Blood Glucose: Pancreas releases the hormone insulin into the blood in response to the high blood glucose condition. Low Blood Glucose: Pancreas release the hormone glucagon into the blood from alpha cells to restore blood glucose. o Discovery of Insulin (1921) Experiment 1: Removed the pancreas from a dog, which resulted in a rise in blood glucose. Also resulted in extreme thirstiness, which resulted in frequent urination. The dog became weaker, and weaker, and eventually died. The dog developed diabetes. Experiment 2: Removed the pancreas from the dog, and tested it. It was sliced and frozen in a mixture of water and salt. When the pieces were half frozen, it was ground up and filtered. The resulting extract was injected into the dog, whom was cured of diabetes. Functions of Insulin o Net effect: Lowers blood glucose levels by: Promoting glycogen synthesis in the muscle, liver, and fat. Increasing glucose uptake within the cells, but only in the muscle and fat cells. Muscle cells take in a much greater amount though. Reduces gluconeogenesis Gluconeogenesis: Process of making glucose Happens in the liver, but also in the kidney. Functions of Glucagon o Acts in the liver to breakdown glycogen. Is released back into the blood (glycogenolysis) Causes the liver to synthesis glucose from non-carbohydrate precursors (gluconeogenesis) Blood Glucose: The Adrenal Glands o Lies on the kidneys. o Releases a hormone, epinephrine. Causes quick conversion of glycogen to glucose in the liver. Improper Regulation of Blood Glucose o Hyperglycemia: High blood glucose Diabetes - Type 1, Type 2, Gestational o Hypoglycemia: Low blood glucose Reactive hypoglycemia, fasting hypoglycemia. o Type 1 Diabetes Often begins in late childhood. Generally associated with a decreased release of insulin from pancreas. Is an immune system disorder, resulting in the destruction of the insulin-producing cells. Treated primarily by insulin therapy. o Type 2 Diabetes Most common form of diabetes, accounting for 90-95% of all cases. Affects about 9% of the U.S. population. 12.7% of Alabama population has type 2 diabetes. Development: Is associated with obesity, ethnicity and also has a genetic component. Pre-Diabetes: Body begins to become resistant to the effects of insulin Results in pancreas making more insulin, then pancreas starts to make less insulin, resulting in high blood glucose. Treatment: Insulin, oral medication, diet and exercise. Complications: CVD, Kidney disease, nerve damage, blindness, and infections Carbohydrate Need o Recommendation vary widely. o RDA: 130 grams per day for adults o Food and Nutrition Board: 45-65% of calories o Carbs In food groups: High: Grains - 15 grams per serving Fruits - 18 grams per serving Milk - 12 grams per serving Low: Nuts: 4 grams per serving Meat and Eggs: 0 grams per serving Veggies: 5 grams per serving Glycemic Index o Ratio of the blood glucose response to a given food compared to a standard. o Based on 50 grams of carbohydrate. o Influenced by a number of factors: Starch structure Fiber content Food processing and physical structure Other macronutrients in food. Glycemic Load o Glycemic index time the amount of carbohydrate in a serving divided by 100. o Can better predict blood glucose response. o More useful than the glycemic index. Problems with High glycemic index/load foods o Very high glucose levels. o Chronically increased insulin levels o Leads to high triglyceride levels, increased fat production. o Amore rapid return of hunger after a meal, increased tendency for blood to clot. Sweeteners o Nutritive sweeteners: Sugar, high-fructose corn syrup, honey o Sugar Alcohol - Sorbitol, Xylitol 2.6 kcal/gram Slow to metabolism to glucose o High-Fructose Corn Syrup: Made with 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 Yields no kcals Examples: Saccharin- Sweet 'N Low (pink) Aspartame- Equal (blue) Sucralose- Splenda (yellow) Alternative sweeteners are sweeter than sucrose o GRAS: Generally Regarded As Safe Extensive scientific research has demonstrated the safety of the 5 low-calorie sweeteners o Aspartame: Complaints of sensitivity Headaches, dizziness, seizures, nausea, etc. Acceptable daily intake: 50 mg per kg body weight. Warning label for Phenylketonuria (PKU) How Much Fiber Do We Need? o A.I. is 25 g/day for women o A.I. is 38g/day for men o A.I. has been set to reduce the risk of cardiovascular disease and possibly diabetes. o DV is 25 grams for 2000 kcal diet o Average U.S. Intake: 14 grams per day for women 17 grams per day for men o Too Much Fiber Greater than 60 grams per day. Extra fluids are needed May increase availability of some vitamins and minerals. Dietary Fiber o Starches are digestible. o Fiber is NOT digestible. Arrives at the colon intact. We don’t have the correct enzymes to break the bonds in the fiber. o Dietary fiber is a group of complex polysaccharides. They have similar characteristics, mostly made up of indigestible plant polysaccharides. Types of Fiber o Insoluble or non-fermentable fiber Cellulose Hemicellulose Lignins o Soluble or Viscous fiber Pectins, Gums, Mucilage Fruits, veggies, rice bran, psyllium seed o Functional Fiber Insulin, oligofructose Added to food Is resistant to digestion but fermentable Stimulates the growth of good bacteria. Evidence based for designation Whole Grains o 9 out of 10 people don't meet the whole grain recommendations of three servings per day. o Look beyond front label to list of ingredients Food Labels o Doesn't separate insoluble and soluble fiber. o Total Fiber = dietary + functional fiber Health Benefits of Adequate Fiber o Insoluble fiber adds mass to the feces, preventing constipation o Constipation can increase the risk of developing Hemorrhoids Diverticula o Soluble fiber Attracts water Delays stomach emptying Promotes feeling of satiety Slows down glucose absorption from the small intestine, lowering the need for insulin. Inhibits the absorption of cholesterol and bile acids in bile, lowering blood cholesterol o Both Soluble and Insoluble Fiber Aids in weight control Reduced risk of colon cancer
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