Chapter 4: The Carbohydrates

HSD 240 – ONLINE CHAPTER 4: THE CARBOHYDRATES: SUGAR STARCH, GLYCOGEN, AND FIBER Carbohydrates play a role in the global carbon cycle Plants CO2 + H2O + energy = glucose Humans Glucose= CO2 + H2O and used again by plants to make glucose GLUCOSE – PREFERRED FUEL FOR MOST BODY FUNCTIONS Preferred source of energy for the brain and sole source of energy for RBCs Starch Foods (complex carbohydrates) are the preferred source of glucose Carbohydrates (carbon + water) CHO- carbon, hydrogen, oxygen ●​ Compounds composed of simple or multiple sugars ●​ Long sugar units – complex carbohydrates – starch and fiber ●​ Small sugar units – simple sugars – not as useful in peoples diets – the source makes a difference Sugars Monosaccharides – single sugars ●​ Glucose – along with glucose the most common monosaccharide in nature ●​ Fructose – found in sugar, honey and part of table sugar ●​ Galactose – found in milk Disaccharides ●​ Sucrose = glucose + fructose; table sugar ●​ Lactose = glucose + galactose; milk sugar; predominant CHO in human milk ●​ Maltose = glucose + glucose Starch ●​ Strands of thousands of glucose units strung together - polysaccharides ●​ Plants storage form of glucose (e.g. corn stores starch in its corn kernels; starch, water insoluble so it is not washed away and the starch can be used the next season to help a new plant grow – fascinating!!) ●​ Nutritive for human beings Glycogen ●​ Chains are longer and more highly branched; the way animals store glucose ●​ Store in the LIVER and MUSCLE tissue Fiber ●​ Provide supporting structures for leaves, stems, and seeds ●​ Most fibers are polysaccharides (polymers of glucose) ●​ Bonds cannot be digested by human enzymes ●​ Vulnerable to breakdown by human bacteria in our digestive tract ●​ Two types of fiber: soluble and insoluble The Need for Carbohydrates ●​ Glucose critical energy source for nervous system – brain ●​ Starchy whole foods are that supply complex carbohydrates – especially fiber rich ones – are the preferred sources of glucose in the diet. Avoid carbohydrates? ●​ Only 4 kcal/gram ●​ Avoid refined carbohydrates and added sugars – mostly sucrose and fructose – that provide few or no nutrients ●​ Whole grains, legumes, nuts, seeds, fruits, vegetables, lower the risk of many chronic diseases Why Recommend Fiber-rich-foods? 1.​ Lower cholesterol and heart disease risk 2.​ Blood glucose control – reduced risk of diabetes 1 3.​ Maintenance of a healthy digestive tract – reduced risk of constipation, hemorrhoids, appendicitis, diverticula 4.​ Digestive tract cancers – reduced risk of colon and rectum 5.​ Healthy weight management ●​ Figure 4-4: Characteristics, Sources, and Health Effects of Fiber ●​ Figure 4-5: Fiber Composition of Common Foods Recommendations and Intakes ●​ USDA Food Patterns o​ Increase intake of whole fruits and vegetables, ,make at least half the grain choices whole grains, and choose legumes several times per week, ●​ DRI​ 38 gms/day men ages 19-50 30 gms/day men ages 51 and up 25 grams/day women ages 19-50 21 grams/day women 51 and up Foods contain a mixture of fibers Consumer Corner: Finding Whole-Grain Foods Recommendation – half of day’s grains to be whole-grains ●​ Germ – especially rich in vitamins and minerals ●​ Endosperm – soft white part, contains starch and protein ●​ Bran – rich in nutrients and fiber ●​ Husk (chaff) – dry, inedible part – good for animal feed ●​ Figure 4-9. Nutrients in Whole-Grain, Enriched White, and Unenriched White Breads US Enrichment act passed by Congress in 1942 ​ Iron, niacin, thiamin, and riboflavin be added to refined grain products ​ 1996 folate was added to the list Table 4-4: Terms that Describe Grain Foods Figure 4-10: Grain Labels Compared From Carbohydrate to Glucose Mouth ●​ Fiber, polysaccharides, and monosaccharides ●​ Polysaccharides [enzyme – salivary amylase] disaccharides (maltose) and smaller polysaccharides Stomach ●​ Starch digestion ceases ●​ Enzymes which are made of protein are deactivated by gastric juices and HCL – except for the enzyme that digests proteins Small Intestine ●​ Polysaccharides [pancreatic enzyme – amylase] smaller polysaccharides and eventually to disaccharides ●​ Disaccharides – split by enzymes on surface of intestinal cell wall Maltose [maltase] glucose + glucose Sucrose [sucrase] glucose + fructose Lactose [lactase] glucose + galactose ●​ Monosaccharides enter capillaries and go to liver via portal vein Liver ●​ Takes galactose and converts it to glucose (or fat) ●​ Travels through the circulatory system to feed the cells ●​ Or stored as GLYCOGEN in the liver and muscles ●​ Essentially all CHO are delivered to the tissues in the form of glucose Colon ●​ Fiber ●​ Note: Resistant starch – barley, dried lentils, beans, oatmeal, underripe bananas o​ may be digested but slowly o​ bacteria of colon may break it down 2 o​ may support a healthy colon o​ humans missing alpha-galactosidase to break down polysaccharides of some foods (Beano) Why do some people have trouble digesting milk? Lactose intolerance – lose ability to produce lactase ●​ 75% of the world’s population ●​ 12% in the US ●​ Infants produce abundant lactase to digest human milk ●​ Milk (cheese, yogurt) tolerance and strategies o​ Different degrees of lactose intolerance o​ What can a person with lactose intolerance eat to get the AI for calcium? Lactose Intolerance vs. Milk Protein Allergy The Body’s use of Glucose ●​ Glucose fuels the work of most of the body’s cells ●​ It is ESSENTIAL ●​ Body handles its use of glucose carefully ●​ Uses what it needs and saves what it doesn’t Glycolysis – splitting glucose for energy ●​ A ready made sequence in cells that oxidize carbohydrates through the entire pathway from glucose or starch to H2O and CO2 ●​ Splits 6 carbon sugars (glucose) to 3 carbon units (eventually to pyruvate) which enters the mitochondria from the cytoplasm for further oxidation (Krebs cycle) ●​ In a series of reactions eventually the smaller products cannot reverse and reform glucose – instead they are used to yield energy in the form of ATP (Adenosine Triphosphate), CO2 and H20 ●​ Smaller units can be converted to body fat, but body fat can NEVER be converted to glucose ●​ Some smaller units will be converted into building blocks of proteins (amino acids) ●​ Liver converts extra glucose to fat, a more permanent and unlimited energy storage compounds (instead of glycogen) CHO deficit – 2 problems ●​ No glucose protein must be used for energy (now protein can’t be used for maintenance – including the immune system – and repair); protein-sparing action of CHO ●​ Using fat instead of CHO causes the body to go into ketosis in which unusual by-products of fat breakdown (ketone bodies) accumulate in the blood disturbing normal acid-base balance o​ Ketosis during pregnancy can cause brain damage of the fetus resulting in irreversible mental retardation after birth DRI Minimum ●​ 130 grams per day minimum for the average-sized adult to feed the brain and reduce ketosis o​ MyPlate – Grains, Vegetables, Fruits, Dairy – some naturally occurring sugars in dairy, Sweets – in moderation ●​ Nutrition Facts ❖​ “Sugar” reflects both added and naturally occurring sugars ❖​ Sugars listed among the ingredients are added sugars ●​ CHO energy yield = 4 kcal per gram How is Glucose Regulated in the Body? Storing Glucose as Glycogen ●​ Meal elevated blood glucose levels pancreas releases the hormone INSULIN glucose uptake into tissues muscle and adipose tissue use excess glucose and store it as polysaccharide glycogen (muscle) or as fat (fat cells); liver with the help of INSULIN also takes up excess glucose and makes glycogen Tissue Glycogen Stores ●​ Muscles hoard 2/3 of glycogen to use for physical activity ●​ Brain reserves some ●​ Liver stores remainder to use willingly (not selfish) when supply runs low 3 The Release of Glucose from Glycogen Blood glucose levels drop pancreas releases the hormone GLUCAGON break down glycogen [enzymes within the liver] FREE GLUCOSE Fight-or-Flight ●​ Epinepherine breaks down liver glycogen as part of body’s defense mechanism in times of danger Handling Excess Glucose ●​ Carbohydrate stored as fat o​ Enzymes convert excess glucose to fat o​ THINK FITNESS CHO and weight maintenance ●​ 45-65% of total kcal ●​ 4 kcal/gram ●​ Complex carbohydrates The Glycemic Index of Food ●​ Different foods effect the way insulin responds to food ●​ A measure of the extent to which a food raises blood glucose concentrations and elicits an insulin response to pure glucose ●​ Figure 4-13 Glycemic Load ●​ Takes into account typical amount of food eaten ●​ Helpful for individuals with diabetes and possibly for weight loss ●​ Low GL foods slowly raise blood sugar levels ●​ Often abundant in soluble fiber Limitations ●​ Eat a combination of foods Diabetes - Chronic condition characterized by elevated blood glucose concentrations; among top ten killers The Dangers of Diabetes ●​ Heart disease, stroke, permanent blindness, fatal kidney failure ●​ Excess glucose has toxic effects – alters metabolism of almost every cell ●​ Chronic inflammation of body tissues accompanies diabetes and may contribute to insulin resistance ●​ Poor circulation - gangrene, amputation Prediabetes – blood glucose elevated; tissue damage progresses silently ●​ Fasting plasma glucose test ●​ HgA1C Important to learn to manage: RD, CDE, endocrinologist 2 main forms: IDDM (Type 1) and NIDDM (Type 2) IDDM ●​ Autoimmune disorder influenced by genetic inheritance ●​ Pancreas no longer able to produce insulin ●​ Blood sugar levels rise to dangerous levels – HYPERGLYCEMIA ●​ Need to take exogenous form of insulin to control blood glucose concentrations ●​ Breastmilk may offer some protection to infants from developing IDDM; Artificial milk derived from cows given to an infant prior to six months of age may trigger the immune system to attack beta cells of the pancreas beta cells die IDDM ●​ Junior Diabetes Research Foundation NIDDM ●​ Insulin resistance ●​ About 90% of the cases ●​ Insulin present, but unable to stimulate cells to take up glucose ●​ Blood glucose AND blood insulin levels high ●​ Oral hypoglycemic agents ●​ Weight loss and exercise can improve glucose tolerance ●​ Preventable in most cases 4 Management of Diabetes ●​ Nutrition o​ Need to keep blood glucose in the normal range o​ Amount of CHO recommended is dependent upon glucose tolerance o​ Complex carbohydrates and low-fat milk o​ US Dietary Exchange System (Appendix B) o​ Timing- food should deliver the same amount of CHO at every meal o​ Want to prevent hypoglycemia o​ Sugar alcohols ok in moderation o​ Artificial sweeteners ●​ Physical Activity Summary: 1.​ Controlled total carbohydrate 2.​ Lower in saturated fat and trans fat 3.​ Adequate in nutrients from food 4.​ Adequate in fiber 5.​ Moderate in added sugars 6.​ Adequate but not too high in protein (kidneys) Hypoglycemia Postprandial hypoglycemia ●​ Rare medical condition in which blood glucose falls too low ●​ Can signal organ damage or disease (e.g. alcohol abuse; too much insulin) Fasting hypoglycemia ●​ What occurs after 8-14 hours of fasting 5