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Chapter 4 Carbohydrates: Sugars, Starches and Fibers Carbohydrates in our Foods • Unrefined foods: foods eaten either just the way they are found in nature or with minimal processing. • Refined: foods that have undergone processing to remove the coarse parts of the original food What is a Whole Grain? • Whole -grain product: include the entire kernel of the grain. • Germ: located at the base of the kernel; is the embryo where sprouting occurs. It is a source of oil and is rich in Vitamin E. • Bran: outermost la yers of the kernel; contain most of the fiber and are a good source of many vitamins and minerals. • Endosperm: makes up most of the kernel. It is primarily starch, but also contains protein along with some vitamins and minerals. • Enrichment: adds back some but not all nutrients lost during processing. Some nutrients added back are thiamin, riboflavin, niacin, iron and folic acid. What is a Refined Sugar? • Nutritionally and chemically identical to sugars that occur naturally in foods. • When separated from thei r plant source, they no longer come with fiber, vitamins, minerals and other substances found in plants. • Empty calories: energy with few additional nutrients. • Account for about 13 % of the calories consumed in a typical American diet. Types of Carbohydrates Simple carbohydrates • Monosaccharides: carbohydrates made up of only one sugar unit. Contain 6 carbon, 12 hydrogen, and 6 oxygen molecules. The three most common are glucose, fructose, and galactose. o Glucose: primary form of carbohydrate used to provide energy in the body; often called blood sugar o Fructose: found in fruits and vegetables. It makes up more than half the sugar in honey and in the high -fructose corn syrup used to sweeten many foods and beverages. o Galactose: part of milk sugar. • Di saccharides: carbohydrates made up of two sugar units. o Maltose: glucose + glucose. Formed whenever starch is broken down. o Sucrose: glucose + fructose. Table sugar. It is the only sweetener that can be called “sugar” on food labels in the US. o Lactose: glucose + galactose. Milk sugar. Complex carbohydrates • Polysaccharides: carbohydrates made up more than two sugar units. • Glycogen: storage form of glucose in humans and animals. Found in the liver and muscles. • Starch: storage form of glucose in plants. • Fiber: type of complex carbohydrate that cannot be digested by human digestive enzymes. o Soluble fiber: dissolves in water or absorbs water and can be bro ken down by intestinal microbiota . ▪ Pectins, gums, and some hemicelluloses ▪ Food sour ces: oats, apples, beans and seaweed. o Insoluble fiber: does not dissolve in water and cannot be broken down by bacteria in the large intestine so it adds bulk to fecal matter. ▪ Primarily the structural parts of plants. ▪ Cellulose, some hemicelluloses and lig nin. ▪ Food sources: wheat, rye bran, broccoli and celery. • Photosynthesis — the process by which plants use the sun’s energy to make carbohydrates from carbon dioxide and water o Plants often convert the glucose made during photosynthesis to starch. When it’s eaten the starch is converted back to glucose. Carbohydrate Digestion and Absorption Carbohydrate Digestion • Disaccharides and complex carbohydrates must be digested to monosaccharides before they can be absorbed into the body. • Digestion begins in the mouth; the enzyme salivary amylase starts breaking down starch into shorter polysaccharides. • In the stomach, salivary amylase is inactivated by acid so no carbohydrate digestion occurs. • In the small intestine, most starch digestion and breakdown of disacc harides occur. Pancreatic amylase completes the job of disaccharide breakdown. • Enzymes attached to the brush border of the small intestinal villi complete the digestion of d isaccharides and oligosaccharides into monosaccharides. • In the large intestine, fib er and other indigestible carbohydrates are partially broken down by bacteria to form short chain fatty acids and gas. Some fiber is excreted in the feces. Lactose Intolerance • The inability to digest lactose due to a reduction in the levels of the enzyme lactase. • Produces gas and abdominal distension, cramping and diarrhea. • Incidence varies among populations. Indigestible carbohydrates • Oligosaccharides: short carbohydrate containing 3 -10 sugar units. o Not digested because they cannot be broken down by human enzymes. • Resistant starch: not digested beca use of the structure of the pla nt or because cooking and processing alter their digestibility. o Examples: legumes, unripe bananas, and cold cooked potatoes, rice and pasta. • Fiber s low s the rate at which nutr ients are absorbed. • Fiber can bind to certain minerals, preventing their absorption. • Speed transit through the intestine by increasing the amount of water and the volume of material in the intestine. Carbohydrate Absorption • The monosaccharides from carboh ydrate digestion enter the portal circulation and travel to the liver. • The liver uses fructose and galactose for energy. • Glucose can be used for energy, stored as liver glycogen, or delivered via circulation to other body tissues, causing the blood glucose levels to rise. • Glycemic response: the rate, magnitude, and duration of the rise in blood glucose that occurs after food is consumed. What a Scientist Sees • Glycemic index: ranking of how a food affects blood glucose relative to the effect of an equivalen t of carbohydrate from a reference food. o Contains a set amount of carbohydrate: 50 grams. o On a glycemic index scale, white bread is 100, potatoes are 90, and kidney beans are 25. • Glycemic load: this compare s the effect of a typical portion of food on blood glucose . Carbohydrate Functions • Main function of carbohydrate is to provide energy. • Other roles in the body: o Galactose is needed by nerve tissue. o In breast -feeding women, galactose combines with glucose to produce lactose. o The monosaccharides ribose and deoxyribose play non -energy roles as components of RNA and DNA. o Ribose is compound of the B vitamin riboflavin. o Oligosaccharides are associated with cell membranes. o Large polysaccharides found in connective tissue provide cushion ing and lubrication. Getting Enough Glucose to Cells • Glucose is an important fuel for body cells. o Brain cells, red blood cells must have glucose to stay alive. • The concentration of glucose in the blood is regulated by the liver and hormones secreted by th e pancreas. • Insulin: hormone made in the pancreas that allows glucose to enter cells and stimulates the synthesis of protein, fat, and liver and muscle glycogen. • Glucagon: hormone made in the pancreas that raises blood glucose levels by stimulating the bre akdown of liver glycogen and the synthesis of glucose. Glucose as a Source of Energy • Cells use glucose to provide energy via cellular respiration. • Uses oxygen to converts glucose to carbon dioxide and water and provide energy in the form of ATP. • Glycolysis: an anaerobic metabolic pathway that splits glucose into two three -carbon pyruvate molecules; the energy released from one glucose molecule is used to make two molecules of ATP. The first step in cellular respiration. • Anaerobic metabolism: metab olism in the absence of oxygen. • Aerobic metabolism: metabolism in the presence of oxygen. It can completely breakdown glucose to yield carbon dioxide, water, and energy in the form of ATP. Carbohydrate and protein breakdown • In the absence of adequate carb ohydrate, amino acids can supply three -carbon molecules that can be broken and used to synthesize glucose. • Body proteins used for glucose synthesis are no longer available to do their job. • Fatty acids break down to two -carbon molecules and cannot be used to synthesize glucose. • Spare protein: sufficient carbohydrate is ensures that protein is not used for glucose synthesis. Carbohydrate and fat breakdown • Ketones or ketone bodies: acidic molecules formed when there is not sufficient carbohydrate to completely metabolize the acetyl -CoA produced from fatty acid breakdown. o Can be used for energy by the heart, muscle, kidney and brain. o Ketones not used for energy are excreted in the urine. • Ketosis: high levels of ketones in the blood. o Occurs during starvation or when consuming a low -carbohydrate weight -loss diet. o Symptoms: reduced appetite, headaches, dry mouth, and odd -smelling breath. o Can increase the blood’s acidity so much that normal body processes are disrupt ed. o Severe ketosis can occur with untreated diabetes and can cause coma and death. Carbohydrates in Health and Disease Diabetes • Diabetes mellitus: disease characterized by elevated blood glucose due to either insufficient production of insulin or decreased sensitivity of cells to insulin. • Damages the heart, blood vessels, kidneys, eyes, and nerves. • Leading cause of adult blindness. • Accounts for over 40% of new cases of kidney failure. • Accounts for more than 60% of non -traumatic lower -limb amputatio ns. • 29.1 million people in the US diagnosed with diabetes. • Another 8.1 million have undiagnosed diabetes. • The incidence of diabetes is greater in minority populations. • Glucose levels in diabetes: o Normal blood glucose: less than 100 mg/100 ml blood after an eight -hour fast. o Prediabetes: fasting blood level between 100 -125 mg/100 ml o Diabetes: fasting blood level at or above 126 mg/100 ml Types of diabetes • Type 1 diabetes: is an autoimmune disease in which insulin -secreting pancreatic cells are destroyed by the body’s immune system. o Accounts for 5 -10% of diagnosed cases. o Usual diagnosis is before age 30. o Must inject insulin to keep blood glucose levels in the normal range. • Type 2 diabetes: characterized by insulin resistance and relative (rather than absolute) insulin deficiency. o Accounts for 90 -95% of all cases. o Insulin resistance: body cells lose their sensitivity ; or amount of insulin secreted is reduced . o Due to genetic and lifestyle factors. • Prediabetes: condition in which glucose levels are above normal but not high enough to be diagnosed as diabetes. o Adjustments in diet and lifestyle can keep prediabetes from progressing to type 2 diabetes. • There are many risk factors for type 2 diabetes including consuming a poor diet that is high in refin ed carbohydrates. • Gestational diabetes: an elevation of blood sugar that is diagnosed during pregnancy. o High levels of glucose in the mother’s blood are passed to the fetus, frequently resulting in a baby who is large for gestational age and at increased risk of complications. o Women with gestational diabetes are at increased risk of developing type 2 diabetes later in life. Symptoms and Complications of diabetes • Early symptoms: frequent urination, excessive thirst, blurred vision, and weight loss. • Long -term complications: damage to heart, blood vessels, kidneys, eyes, and nerves. o Increased risk of heart attack and stroke. o Blindness, kidney failure, and nerve dysfunction. o Infections may lead to amputations of toes, feet, and legs . Mana ging blood glucose • Diet: carbohydrate must be coordinated with exercise and medication o Limit amount of carbohydrates at each meal o Unrefined carbohydrates o Limit satur ated fat and trans fat o Weight management • Exercise: helps achieve and maintain a healthy bod y weight. o Increases cells sensitivity to insulin. • Medication o Type 1 requires insulin by injection. o Type 2 and gestational: may require oral medications or insulin injections. Hypoglycemia • Abnormally low blood glucose levels. o below 70 mg glucose/100 ml blood o Symptoms: irritability, sweating, shakiness, anxiety, rapid heartbeat, headache, hunger, weakness, and sometimes seizures and coma. o Occurs most frequently in people with diabetes as a result of overmedication. • Fasting hypoglycemia: occ urs when an individual has not eaten. o Often related to underlying condition: excess alcohol consumption, hormonal deficiencies or tumors. o Treatment: identify and treat underlying disease. • Reactive hypoglycemia: occurs in response to the consumption of high -carbohydrate foods. o Treatment: small, frequent meals that are low in carbohydrate and high in protein and fiber. Weight Management Carbohydrates and weight loss • Type of carbohydrates consumed can affect hunger and whether weight is gained or lost. • Diet high in unrefined carbohydrates: high in fiber and filling. o Can help promote weight loss. o May be problematic for children who become satiated before meeting nutrient requirements. • Diets high in refined carbohydrate: cause a rapid rise in blood glucose and stimulate release of insulin. o May shift metabolism toward fat storage. • Low carbohydrate diets: lead to weight loss because they reduce insulin levels and raise blood ketone levels, both of which suppress appetite. o Limit food choices le ading to monotony and resulting in reduction of calorie intake. Debate: Is sugar making us sick ? • Issue: Is sugar “toxic”? Few would argue that the sugar calories we consume would be better spent on healthier foods. Sugar has been implicated as a cause of not only dental problems but obesity, diabetes, heart disease, and even cancer. Do the current levels of sugar consumption pose a serious health risk? Heart Disease • A diet high in sugar can raise blood lipid levels and thereby increase the risk of heart disease. • Diets high in fiber from grains, vegetables, and fruits have been found to reduce the risk of heart disease. o Soluble fibers may lower blood cholesterol levels. o May help lower blood pressure, normalize blood glucose levels, and prevent obesity. Dental Caries • Best documented health problem associated with carbohydrate intake. • Occur when bacteria on teeth metabolize carbohydrates, producing tooth -damaging acids. • Prevention: limit intake of sweet or sticky foods and proper dental hygiene. Bowel Hea lth • Fiber and other indigestible carbohydrates add bulk and absorb water in the GI tract. o Make feces larger and softer and reducing the pressure needed for defecation. • Hemorrhoids: swelling of veins in the rectal or anal area. • Diverticulosis: condition in which outpouches form i n the wall of the colon . o Treatment: high fiber diet. • Diverticulitis: inflammation, irritation and pain. o May lead to infection. o Treatment: antibiotics and low -fiber diet. Meeting Carbohydrate Needs Carbohydrate Recommendations • RDA : 130 g/day • Acceptable Macronutrient Distribution Range: 45 – 65% of total calorie intake. • Adequate Intake for fiber: 38 g/day for men and 25 g/day for women. • No Upper Limit has been established for total carbohydrate, fiber or added sugar intake. • Dietary Guidelines 201 5-2020 : limit added sugars to less than 10% of calories . Choosing Carbohydrates Wisely • Use Dietary Guidelines 2015 -2020 and MyP late to make healthy choices • Pros and Cons of Nonnutritive sweeteners o Artificial sweeteners which provide no calories. o FDA has approved acesulfame K, advantame, aspartame, Luo Han Guo, neotame , saccharin, stevia , and sucralose . o When sweeteners are used instead of sugar, calorie intake is reduced. o Can help reduce the incidence of dental caries and manage blood sugar levels. • Interpret food labels o Find foods that are good sources of fiber. o Identify whole -grain products and sources of added sugar. What Should I Eat? Carbohydrates • Make half your grains whole. • Increase your fruits and vegetables. • Limit added sugars