Carbohydrates: Facts to Know Concept 7

Pop Quiz True or False? You don’t need to eat carbohydrates. Plants are our only source of carbohydrates. Popcorn is a whole grain. People who are lactose intolerant need to avoid all dairy products. Insulin is a type of sugar found in the blood. ANSWER ANSWER ANSWER ANSWER ANSWER

What Are Carbohydrates and Why Do You Need Them? A diet staple found mainly in plant-based foods Examples: grains, fruits, vegetables, nuts, and legumes Also found in dairy foods The primary sugar in high-carbohydrate foods is glucose. Photosynthesis: the process by which green plants create carbohydrates using energy from the sun Chlorophyll: the green pigment in plants that absorbs the energy from sunlight to start the process

Photosynthesis: How Glucose Is Made Figure 7.1

What Are Carbohydrates and Why Do You Need Them? Glucose is the most abundant carbohydrate in nature. Plants use glucose as energy or combine it with minerals from soil to make protein or vitamins. Plants link glucose units together and store them in the form of starch.

What Are Simple and Complex Carbohydrates? Monosaccharides and Disaccharides Are Simple Carbohydrates Polysaccharides Are Complex Carbohydrates Starch Is Stored in Plants Fiber Is Not Digestible, but Is Important Grains, Glorious Whole Grains Glycogen Is Stored in Animals

What Are Simple and Complex Carbohydrates? Simple carbohydrates include: Monosaccharides: one sugar unit Disaccharides: two sugar units combined Complex carbohydrates include: Polysaccharides: many sugar units combined

Monosaccharides and Disaccharides Are Simple Carbohydrates The monosaccharides: Glucose: produced by plants Fructose: found in fruit; sweetest of the simple sugars Galactose: simple sugar found in dairy foods The disaccharides are created by combining monosaccharides. Glucose + fructose = sucrose (table sugar) Glucose + glucose = maltose (sugar in grains) Glucose + galactose = lactose (milk sugar)

Monosaccharides and Disaccharides Figure 7.2 a,b

Polysaccharides Are Complex Carbohydrates Polysaccharides are long chains of monosaccharides linked together. Three groups: Starch Fiber Glycogen

Polysaccharides Polysaccharides are long chains of many glucose units joined together in a straight chain or with branches. Figure 7.2c

Polysaccharides Are Complex Carbohydrates Starch is stored in plants. Consists of many glucose units strung in a chain May be straight or branched chains Found in pasta, rice, bread, and potatoes

Polysaccharides Are Complex Carbohydrates Fiber is not digestible, but is important. Dietary fiber: found naturally in foods Functional fiber: added for a beneficial effect Soluble fiber: dissolves in water, viscous Found in fruits, vegetables, beans, and oats Fermented by bacteria in large intestine Moves slowly through intestinal tract; has laxative effect Insoluble fiber: does not dissolve in water Found in seeds, cereal fiber, whole-grain bran, and some fruits and vegetables Moves more quickly through intestinal tract

Grains, Glorious Whole Grains A whole grain is made up of three edible parts: Bran: indigestible outer shell Rich in fiber, B vitamins, phytochemicals, and minerals Germ: the seed Provides vitamin E, heart-healthy fats, phytochemicals, and B vitamins Endosperm: the starchy part of the grain Contains protein, B vitamins, and some fiber (in smaller amounts than the bran)

Grains, Glorious Whole Grains Two categories of grain products: Refined grains are grain kernels stripped of bran and germ, leaving only the endosperm. Enrichment: attempts to restore some of the nutrients lost in refinement by adding back folic acid, thiamin, niacin, riboflavin, and iron Whole grains include the entire edible grain kernel—the bran, the germ, and the endosperm. Consumption of whole grains may reduce risk of heart disease, stroke, and diabetes.

Polysaccharides Are Complex Carbohydrates Glycogen is stored in animals. The form of glucose stored in the liver and muscle cells of humans and animals Can be an important source of glucose for the cells of the body Breaks down when the animal dies and is not available in meat or poultry consumed

Some People Cannot Digest Milk Sugar Lactose Maldigestion Develops with Aging Severe Lactase Deficiency Produces Lactose Intolerance

Lactose Maldigestion Develops with Aging The inability to digest lactose in foods due to inadequate levels of the enzyme lactase A natural part of the aging process 25 percent of Americans affected 75 percent of adults worldwide affected People of some ethnic origins tolerate lactose better than others. Despite lactose maldigestion, many people can still enjoy milk, yogurt, and cheese.

Severe Lactose Deficiency Produces Lactose Intolerance Occurs when maldigestion of lactose results in nausea, cramps, bloating, flatulence, and diarrhea Not the same as a milk allergy Can be improved by: Consuming smaller amounts of dairy at a time Eating dairy foods with a meal or snack rather than by themselves Choosing lactose-reduced dairy products or items with lower lactose levels Taking lactase pills before lactose-containing meals

How Does Your Body Use Carbohydrates? Insulin Regulates Glucose in Your Blood Carbohydrates Fuel Your Body between Meals During Fasting, Your Body Breaks Down Fat and Protein

Insulin Regulates Glucose in Your Blood Hormones are chemical messengers that regulate important conditions in the body. Insulin: a hormone released by the pancreas that helps move glucose into your cells and determines whether it will be used immediately as energy or stored for later Carbohydrate-rich meals increase blood glucose. Elevated blood glucose triggers release of insulin. Glucose can be stored as glycogen in the liver and muscle cells or as fat.

Insulin Directs Excess Glucose into Storage Figure 7.3a

Carbohydrates Fuel Your Body between Meals When blood glucose levels drop, your body calls on its glycogen reserves. Glucagon: a hormone released by the pancreas when blood glucose drops Directs release of glucose from stored glycogen in the liver Signals the liver to manufacture glucose from noncarbohydrate sources such as protein Epinephrine (adrenaline): another hormone that can act on liver and muscle cells to stimulate breakdown of glucose “Fight-or-flight” hormone

The Pancreas Releases Glucagon When Blood Glucose Is Low Figure 7.3b

During Fasting, Your Body Breaks Down Fat and Protein Fasting depletes glycogen stores, which forces the body to rely on breakdown of fat and protein for fuel. Without glucose, fat breakdown is incomplete and creates by-products called ketone bodies. Ketone bodies accumulate in the blood, causing it to be slightly acidic. Leads to ketosis Ketosis often occurs in individuals who are fasting or following strict low-carbohydrate diets. Protein from muscles and organs is also broken down to make glucose during fasting. If fasting continues, death is inevitable.

The Top Five Points to Remember Glucose, fructose, and galactose are simple carbohydrates. Glucose is the preferred fuel for the brain and red blood cells. Two monosaccharides are joined to form disaccharides. Sucrose (table sugar), lactose (milk sugar), and maltose are examples of disaccharides. Many glucose units are joined together to form polysaccharides. Glycogen (found in animal tissue), starch (found in plants), and fiber are examples of polysaccharides.

The Top Five Points to Remember Lactose maldigestion is the inability to properly absorb the milk sugar lactose because of a reduced amount of the enzyme lactase. Blood glucose is maintained in a healthy range by hormones. Insulin directs glucose into your cells. Glucagon increases blood glucose. Ketone bodies are created when fat is incompletely broken down during fasting.

Answers to the Pop Quiz FALSE. You need a minimum amount of carbohydrates daily to fuel your brain. BACK TO QUIZ

Answers to the Pop Quiz FALSE. Dairy products also contain carbohydrates in the form of a sugar called lactose. BACK TO QUIZ

Answers to the Pop Quiz TRUE. Popcorn, along with brown rice, bulgur, and oatmeal, is a whole grain. BACK TO QUIZ

Answers to the Pop Quiz FALSE. Many people who are lactose intolerant are still able to enjoy some dairy products, especially if eaten with meals. BACK TO QUIZ

Answers to the Pop Quiz FALSE. Insulin is a hormone produced by the pancreas. It helps regulate glucose levels in your blood. BACK TO QUIZ