CARBOHYDRATES

The term “carbohydrate” refers to a group of molecules composed of carbon, hydrogen, and oxygen. There are two groups: Simple carbohydrates (also called “sugars”) Complex carbohydrates

The term “carbohydrate” refers to a group of molecules composed of carbon, hydrogen, and oxygen. There are two groups: Simple carbohydrates (also called “sugars”) Complex carbohydrates In fact, they are related: The complex carbohydrates are formed by linking together many simple carbohyrates and The simple carbohydrates can be formed by breaking apart the complex carbohydrates We get carbohydrates in our diets from eating plants and, to smaller degree from milk and meat.

Simple Carbohydrates: The simple carbohydrates are the monosaccharides and the disaccharides

Simple Carbohydrates: The simple carbohydrates are the monosaccharides and the disaccharides Although there are dozens of known monosaccharides and disaccharides, only a small number are important nutritionally because they are found in our food. Monosaccharides: All have formula C6H12O6

Simple Carbohydrates: Monosaccharides Glucose (also called “dextrose”) is the most abundant and most important monosaccharide.

Simple Carbohydrates: Monosaccharides Glucose (also called “dextrose”) is the most abundant and most important monosaccharide. All green plants produce glucose from carbon dioxide, water, and sunlight (energy) Gives food a sweet taste Glucose is the primary “fuel molecule” our cells use to produce energy so It is the sugar carried around the body in the blood

Simple Carbohydrates: Monosaccharides Fructose (also called “levulose” or “fruit sugar”) is also very sweet

Simple Carbohydrates: Monosaccharides Fructose (also called “levulose” or “fruit sugar”) is also very sweet Occurs naturally in fruits, vegetables, honey, and corn syrup. Some cells can use fructose as a fuel molecule, but most cells convert it to glucose instead

Simple Carbohydrates: Monosaccharides Galactose - rarely found alone in nature Usually combined with glucose

Simple Carbohydrates: Monosaccharides Galactose - rarely found alone in nature Usually combined with glucose Found in milk Cells convert galactose to glucose for energy May be part of cell membranes

Simple Carbohydrates: Disaccharides Disaccharides are two monosaccharides linked together

Simple Carbohydrates: Disaccharides Disaccharides are two monosaccharides linked together Three disaccharides are dietarily important: Sucrose Lactose Maltose All have formula C12H22O11

Simple Carbohydrates: Disaccharides Sucrose = glucose + fructose Found in sugarcane, sugarbeets “Table Sugar” – only sweetener that can be called “sugar” on food labels in United States

Simple Carbohydrates: Disaccharides Lactose = glucose + galactose “Milk Sugar”

Simple Carbohydrates: Disaccharides Maltose = glucose + glucose Found in partially digested starch and in germinating cereal grains

Complex Carbohydrates Chains of two or more monosaccharides Oligosaccharides = shorter chains Polysaccharides = longer chains 17

Complex Carbohydrates: Oligosaccharides Consist of 3-10 monosaccharides Found in legumes, milk Forms receptors on many cell membranes Not digestible by humans = fiber May be added to food: inulin oligofructose raffinose maltotriose 18

Complex Carbohydrates: Polysaccharides Starch: How plants store energy Found in grains, legumes, and tubers Long chains of glucose units: Amylose—straight chains Amylopectin—branched chains 19

Complex Carbohydrates: Polysaccharides Glycogen How animals (including humans) store energy Found in meat, liver Long, branching chains of glucose units: Formed in liver and muscle when blood glucose levels are high Can be broken down to provide glucose when blood glucose levels get low 20

Complex Carbohydrates: Polysaccharides Cellulose Indigestible chains of monosaccharides = “fiber” - speeds up gastrointestinal movement - increases fecal mass - slows breakdown of starch - slows absorption of glucose Found in all plants, “Functional” fiber: isolated and added to foods Can be use as a supplement 21

Complex Carbohydrates: Polysaccharides Other forms of fiber = Indigestible chains of monosaccharides Pectins Gums Lignans Beta glucans Chitins Found in all plants, “Functional” fiber: isolated and added to foods Can be use as a supplement 22

Complex Carbohydrates 23

Complex Carbohydrates: Dietary fiber: Possible role in weight control Better control of blood glucose Reduced risk of heart disease Healthier gastrointestinal functioning Negative effects of excess fiber Increased water consumption Can bind small amounts of minerals 24

Carbohydrate Digestion: Complex carbohydrates (amylose, amylopectin) broken down to form disaccharides and monosaccharides: Mouth: Salivary amylase begins digestion Stomach: No carbohydrate digestion Small intestine: Pancreatic amylase finishes digestion 25

Carbohydrate Digestion: Disaccharides (sucrose, maltose, lactose) broken down to form monosaccharides: Small intestine: Pancreatic enzymes Enzymes from intestinal cells (sucrase, maltase, lactase) 26

Carbohydrate Digestion: These enzymes are highly specific For example: - Amylase digests amylose but not amylopectin - Lactase digests lactose but not maltose or sucrose - Maltase digests maltose but not lactose or sucrose - Sucrase digests sucrose but not maltose or lactose Remember: Some carbohydrates can not be digested; fiber & “resistant” starch 27

Carbohydrate Absorption: Monosaccharides are absorbed from the small intestine 28

Carbohydrate Absorption: Monosaccharides are absorbed from the small intestine and carried by the blood to the liver 29

Carbohydrate Absorption: Monosaccharides are absorbed from the small intestine and carried by the blood to the liver Liver: Converts other monsaccharides to glucose Stores excess glucose as glycogen 30

Carbohydrate Absorption: Monosaccharides are absorbed from the small intestine and carried by the blood to the liver Liver: Converts other monsaccharides to glucose Stores excess glucose as glycogen Liver: Breaks down glycogen to release glucose back into the blood when needed. 31

Carbohydrate Metabolism: Glucose is our primary fuel source so It is important to maintain normal blood glucose levels and It is important for glucose to get from the blood into cells 32

Carbohydrate Metabolism: Glucose is our primary fuel source so It is important to maintain normal blood glucose levels and It is important for glucose to get from the blood into cells These processes are primarily regulated by two hormones Insulin Glucagon Both are secreted by the pancreatic islets 33

Carbohydrate Metabolism: 34

Carbohydrate Metabolism: Insulin promotes: (i) Energy storage glucose glycogen (glycogenesis) (ii) Protein synthesis glucose amino acids protein (iii) Fat synthesis glucose fatty acids triglycerides(fat) 35

Carbohydrate Metabolism: Disorders Normal Blood Glucose: 70-110 mg/100 ml of blood 36

Carbohydrate Metabolism: Disorders Normal Blood Glucose: 70-110 mg/100 ml of blood Persistent high blood glucose levels = Hyperglycemia Insufficient insulin >125 mg/100 ml Too much glucagon Most common cause = diabetes mellitus 37

Carbohydrate Metabolism: Disorders Normal Blood Glucose: 70-110 mg/100 ml of blood Persistent high blood glucose levels = Hyperglycemia Insufficient insulin >125 mg/100 ml Too much glucagon Most common cause = diabetes mellitus Persistent low blood glucose levels = Hypoglycemia Too much insulin <50 mg/100 ml Insufficient glucagon Most common causes = insulin overdose in diabetes starvation strenuous exercise 38

Carbohydrate Metabolism: Disorders Diabetes Mellitus: Glucose unable to enter cells so Blood glucose levels rise (hyperglycemia) Complications: Hypertension Heart damage Kidney damage Nerve damage Blood vessel damage Eye damage 39

Carbohydrate Metabolism: Disorders Diabetes mellitus: Type 1 or “insulin dependent” diabetes: Lack of insulin production Type 2 or “insulin independent” diabetes: Cells are resistant to insulin 40

Carbohydrate Metabolism: Disorders Diabetes mellitus: Type 1 or “insulin dependent” diabetes: Lack of insulin production Type 2 or “insulin independent” diabetes: Cells are resistant to insulin Usually present as “prediabetes” first Gestational diabetes: occurs during pregnancy 41

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Carbohydrate Metabolism: Disorders Diabetes mellitus: Best prevention: Healthful diet Regular exercise Healthy weight Don’t smoke Monitor blood sugar if you have genetic predisposition 43

Carbohydrates: Recommended carbohydrate intake: Recommended Daily Allowance = 130 grams per day Acceptable Macronutrient Distribution Range = 45–65% of calories 44

Carbohydrates: Recommended carbohydrate intake: Recommended Daily Allowance = 130 grams per day Acceptable Macronutrient Distribution Range = 45–65% of calories Choose carbohydrates wisely: fiber-rich fruits vegetables whole grains high-fiber cereal Because: Not all carbohydrate sources have the same effect on blood glucose levels 45

Carbohydrates: Each type of food has a glycemic index which measures its effects on blood sugar levels.

Carbohydrates: Each type of food has a glycemic index which measures its effects on blood sugar levels. Carbohydrates that break down quickly during digestion and release glucose rapidly for absorption into the bloodstream have a high glycemic index

Carbohydrates: Each type of food has a glycemic index which measures its effects on blood sugar levels. Carbohydrates that break down quickly during digestion and release glucose rapidly for absorption into the bloodstream have a high glycemic index Carbohydrates that break down more slowly, releasing glucose more gradually for absorption into the bloodstream, have a low glycemic index.

Carbohydrates: Low glycemic index: Most vegetables, fruits, legumes, (55 or less) whole grains, nuts, milk, citrus juices, foods low in carbohydrates Moderate glycemic index: Whole wheat products, honey, (56 to 69) brown or basmati rice, bran, baked potato, sweet potato High glycemic index: White bread, white rice, breakfast (70 and above) cereals, waffles, chips, candy, table sugar (Pure glucose: glycemic index = 100) 49

Carbohydrates: Moderating sugar intake: Choose food with lower glycemic index Use less added sugar Limit soft drinks, sugary cereals, and candy Choose fresh fruits or those canned in water or juice 50

Carbohydrates: Natural and Artificial Sweeteners Nutritive sweeteners Natural sugars Sugar alcohols Non-nutritive sweeteners Saccharin Aspartame Acesulfame K Sucralose 51

Let’s move on to the lipids next