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Transcript
Chapter 4 Carbohydrates: Sugar, Starches and Fiber Carbohydrates in Our Diet Carbohydrates make up most of the energy in a healthy diet. Grains are sources of carbohydrates. Refined carbohydrates lack fiber and many rich nutrients. Unrefined carbohydrates are healthier to eat. Unrefined and Refined Foods Whole Grains Whole grains are made up of bran: containing fiber and vitamins germ: mainly protein and vitamins endosperm: starch, protein, vitamins, and minerals Empty Calories Many processed/ready to eat foods contain added sugar that reduces nutrient density (empty calories) Types of Carbohydrates Glucose, fructose and galactose are simple carbohydrates. Glucose is the blood sugar and found in cells. Sucrose is made up of a molecules of glucose and a molecule of fructose is a disaccharide. Maltose is made up of two glucose molecules. Lactose contains one glucose and one galactose. Monosaccharides Dissaccharides Simple carbohydrates have one or two molecules of single sugars. maltose, sucrose and lactose are simple carbohydrates. Glucose, galactose and fructose are single carbohydrates. Glucose is the blood sugar and source of energy from carbohydrates. Galactose is milk sugar important in producing milk in lactating women and animals. Dissaccharides Complex Carbohydrates Complex carbohydrates contain many molecules of glucose. Starch, glycogen and cellulose are complex carbohydrates. Starch and glycogen are synthesized by a chain of glucose molecules joined by alpha 1–4 and 1–6 bonds they also have branched chain attached. Fiber (cellulose) is a chain of glucose molecules joined by beta 1–4 bond that human intestine does not produce the enzyme to digest it. Complex Carbohydrates Glucose is Produced by Plants through Photosynthesis Chemistry of Carbohydrates Starch is stored in the grains, stems and root of the plant. Fiber is found in the bran of the grains, stem, leaf, and other structures of the plants. There are two types of fiber in the plant varieties: Soluble fiber in fruits, oats and legumes Insoluble fiber mostly in grains and vegetables Soluble and Insoluble Fiber Pectin Beans Fiber Humans do not produce enzyme to digest fiber—therefore, no calories from fiber. Fiber provides many health benefits to humans: Insoluble fiber: provides bulk in the intestine to ease elimination. prevents constipation, diverticulitis, appendicitis, and may prevent colon cancer. Soluble fiber: combines with bile, eliminate it, preventing elevated blood cholesterol Carbohydrate Digestion & Absorption Mouth Small intestine Absorption through the small intestinal villi Digestive enzymes from pancreas Active absorption Passive diffusion Large intestine Elimination of undigested starch and fiber Modification of intestinal microflora Role of the pancreas Carbohydrate Digestion Glycemic Index Different carbohydrate containing foods are absorbed at different rate. Simple carbohydrates and potato starch are absorbed fast and make a large spike in the blood sugar (a high glycemic index) causing a high insulin response. Beans, legumes and some mixed foods are absorbed slower and have lower glycemic index. Glycemic Index Carbohydrate Functions Getting glucose to the cells, role of insulin. Problems of glucose metabolism Type 1 diabetes, pancreases loss of insulin producing ability. Autoimmune problem Type 2 diabetes increased body fat cells causing resistance to insulin delivery of glucose to the cells Role of insulin in regulating blood glucose levels Functions of Monosaccharide Absorbed monosaccharids enter liver where galactose and fructose are converted to glucose. Glucose enters the blood and circulates. Insulin helps glucose enter the cells for energy, stimulate the synthesis of liver and muscle glycogen, protein, fat. Glucagon stimulates the breakdown of liver glycogen and synthesis of glucose Glucose also is a part of genetic DNA, RNA, ATP and other functional molecules in the body. Blood Glucose Regulation Cellular Carbohydrate Metabolism In cells, glucose is metabolized to produce energy. There are two pathways for producing energy: Anaerobic pathway (incomplete metabolism) with production of lactate. Happens in absence of oxygen. Resulting in lower energy production Aerobic pathway (complete metabolism) with end products of CO2 and H2O. Happens when oxygen is present. Produces lot more energy. Cellular Respiration Breakdown of Fat and Protein In the absence of carbohydrates body breaks down protein to form glucose to feed the brain. About ½ of amino acids skeletons can produce glucose Other amino acids produce ketone acidic molecules that changes the pH of body environment to acid. Body also breaks down the stored fat to provide energy for body needs Fat breakdown in the absence of carbohydrates results in ketone production. Ketone bodies are harmful to the body and are excreted through the urine. Severe ketosis can occur with untreated diabetes and can cause coma and even death. Ketone Formation Carbohydrates and Health Are carbohydrates good or bad for you? What kind of carbohydrates are beneficial to health? Whole grains, complex carbohydrates foods are healthy carbohydrates. What kind are not healthy carbohydrates to consume? Refined carbohydrates and food with added sugar are not healthy and may cause risk of chronic diseases. Diabetes Carbohydrates are generally blamed for diabetes. The interesting fact is again which kind of carbohydrates are to be blamed. Whole grain and complex carbohydrates prevent type 2 diabetes by preventing fat cells accumulation in the body. Refined carbohydrates increase empty calories in the diet may cause weight gain, increase resistance to insulin causing type 2 diabetes. Diabetes Type 1 diabetes is due to lack of production of insulin from pancreas causing blood glucose to elevate. It can be controlled by a diet very low on fast absorbing starches (potato) and refined sugars. A diet high in fiber and whole grains help slow absorption and prevent fast rise in blood sugar. In sever cases insulin must be injected to regulate blood sugar levels. Blood Glucose Levels in Diabetes Diabetes Incidences of diabetes in the US is on the rise. Certain racial groups are more susptible to diabetes than others. Lifestyle, dietary habits physical activity and environment also play a role. Managing diabetes with diet, exercise and medication. Symptoms and complications of diabetes. Incidence of Diabetes Other Health Problems Hypoglycemia: Dental caries: Reactive hypoglycemia Fasting hypoglycemia Dental hygiene Refined sugars Carbohydrates and weight management: Which kind to consume? Carbohydrates and Weight Management Carbohydrates & Body Weight Carbohydrates and weight management. Role of refined carbohydrates in storage of fat. Role of insulin in body fat accumulation. The consequence of low or no carbohydrate diets? Ketosis and ketogenic diets Role of ketones in weight loss Benefits and harms of nonnutritive sweeteners. Nonnutritive Sweeteners Carbohydrates and Heart Disease Carbohydrates and Heart Disease Consuming foods high in soluble fiber reduce cholesterol synthesis by liver. Soluble fiber in legumes, fruits, oats, brown rice, etc. bind with bile in the intestine, removing it from the body preventing bile reabsorption, and cholesterol re-synthesis. Soluble fiber may also reduce blood cholesterol by other means. Cholesterol and Soluble Fiber Carbohydrates and Heart Disease Diets with high insoluble help reduce risk of heart disease by: Reducing absorption of starch and sugars. Keeping blood glucose normal Reducing food intake by filling the stomach and reducing the appetite. Preventing obesity Reducing blood pressure. Preventing formation of diverticula Diverticula Intestinal Health and Fiber Insoluble fiber is not digested, absorbs water in the intestine and increase in volume conferring benefits: Softens the stool, making elimination easy. Preventing constipation, diverticulitis, appendicitis, hemorrhoids, and possibly colon cancer. Speed up the movement of waste materials from the bowl. Modify the bowl micro flora environment positively. Meeting Carbohydrate Needs Carbohydrates intake is to meet the needs of: Recommendations are: Adequate blood glucose levels to meet the brain, red blood cells and nerves energy requirements (about 130 grams/day). Minimum carbohydrate intake to prevent ketosis is 100 grams/day 45% – 65% of total daily calorie intake should come from complex carbohydrates. In the US diet, the right percentage of calories consumed from carbohydrates, but it is mostly refined or added sugars. Healthy Carbohydrate Choices Make at least half of your grains whole grains make half your plate fruits and vegetables. 2011 http://www.choosemyplate.gov/food-groups/ Choosing Carbohydrates Wisely End of Chapter 4 Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein.
