Chapter 4 - Carbohydrates

In absence of carbs, protein and fats are used for energy. When no carbs available, liver cannot break down fat completely, it instead produces small ketone bodies. May enter ketosis.

What are the consequences of eating too little carbs?

amylopectin

A branched-chain polysaccharide composed of glucose units.

disaccharides

Carbohydrates composed of two monosaccharide units linked by a glycosidic bond. They include sucrose (common table sugar), lactose (milk sugar), and maltose.

enzymes

Carbs are digested by ___ from the mouth, pancreas and small intestine and absorbed as monosaccharides.

starch, fiber and sugar

Carbs are found mainly in plant foods and ___, ___ and ___.

complex carbs

Chains of more than two monosaccharides. May be oligosaccharides or polysaccharides.

alpha (α) bonds

Chemical bonds linking two monosaccharides (glycosidic bonds) that can be broken by human intestinal enzymes, releasing the individual monosaccharides. Maltose and sucrose contain ___.

beta (β) bonds

Chemical bonds linking two monosaccharides (glycosidic bonds) that cannot be broken by human intestinal enzymes. Cellulose contains ___.

refined sweeteners

Composed of monosaccharides and disaccharides that have been extracted and processed from other foods.

sugar alcohols

Compounds formed from monosaccharides by replacing a hydrogen atom with a hydroxyl group (-OH); commonly used as nutritive sweeteners. Also called polyols.

benefits: • bowel regularity • reduced blood cholesterol • increased feeling of fullness • reduced risk of heart disease • improved nutrient intake if fiber intake was increased by consumption of fruits and vegetables too much: constipation or diarrhea, gas, bloating, calorie insufficiency, and decreased mineral absorption. too little: increased risk for constipation, diverticulitis, and heart disease.

List the benefits of eating more fiber. What are the consequences of eating too much? Too little?

polysaccharides

Long carbohydrate chains composed of more than 10 sugar molecules. ___ can be straight or branched.

thaumatin

Mixture of sweet-tasting proteins from a West African fruit. Approximately 2,000 times sweeter than sucrose and has a licorice aftertaste. Breaks down when heated to cooking temperatures.

The branched chain structure of glycogen provides many end units for enzymes to attack. Compared to a straight chain of glucose, this allows enzymes to break it down more quickly and rapidly release glucose.

What advantage does the branched-chain structure of glycogen provide compared with a straight chain of glucose?

aspartame

An artificial sweetener composed of two amino acids and methanol. It is 200 times sweeter than sucrose. Its trade name is NutraSweet.

d-tagatose

An artificial sweetener derived from lactose that has the same sweetness as sucrose with only half the calories

sucralose

An artificial sweetener made from sucrose; it was approved for use in the United States in 1998 and has been used in Canada since 1992. ___ is nonnutritive and about 600 times sweeter than sugar.

neotame

An artificial sweetener similar to aspartame, but one that is sweeter and does not require a warning label for phenylketonurics.

acesulfame K

An artificial sweetener that is 200 times sweeter than common table sugar (sucrose). Because it is not digested and absorbed by the body, ___ contributes no calories to the diet and yields no energy when consumed.

saccharin

An artificial sweetener that tastes about 300 to 700 times sweeter than sucrose.

phenylketonuria

An inherited disorder caused by a lack or deficiency of the enzyme that converts phenylalanine to tyrosine.

monosaccharides

Any sugars that are not broken down further during digestion and have the general formula CnH2n0n, where n = 3 to 7. The common ___ glucose, fructose, and galactose all have six carbon atoms (n = 6).

dietary fiber

Carbohydrates and lignins that are naturally in plants and are nondigestible; that is, they are not digested and absorbed in the human small intestine.

liver

The ___ converts the monosaccharides fructose and galactose to glucose.

blood glucose levels

The amount of glucose in the blood at any given time. Also known as blood sugar levels.

psyllium

The dried husk of the psyllium seed.

husk

The inedible covering of a grain kernel. Also known as the chaff.

germ

The innermost part of a grain, located at the base of the kernel, that can grow into a new plant. The ___ is rich in protein, oils, vitamins, and minerals.

endosperm

The largest, middle portion of a grain kernel. The ___ is high in starch to provide food for the growing plant embryo.

bran

The layers of protective coating around the grain kernel that are rich in dietary fiber and nutrients.

energy

The main function of carbs is to supply ___.

starch

The major storage form of carbohydrate in plants; ___ is composed of long chains of glucose molecules in a straight (amylose) or branching (amylopectin) arrangement.

total fiber

The sum of dietary fiber and functional fiber.

glucose, fructose, galactose

Three monosaccharides important in human nutrition...

diabetes mellitus

A chronic disease in which uptake of blood glucose by body cells is impaired, resulting in high glucose levels in the blood and urine. Type 1 is caused by decreased pancreatic release of insulin. In type 2, target cells (e.g., fat and muscle cells) lose the ability to respond normally to insulin.

fructose

A common monosaccharide containing six carbons that is naturally present in honey and many fruits; often added to foods in the form of high-fructose corn syrup. Also called levulose or fruit sugar.

glucose

A common monosaccharide containing six carbons that is present in the blood; also known as dextrose or blood sugar. It is a component of the disaccharides sucrose, lactose, and maltose and various complex carbohydrates.

stevioside (stevia)

A dietary supplement, not approved for use as a sweetener, that is extracted and refined from Stevia rebaudiana leaves.

lactose

A disaccharide composed of glucose and galactose; also called milk sugar because it is the major sugar in milk and dairy products.

sucrose

A disaccharide composed of one molecule of glucose and one molecule of fructose joined together. Also known as table sugar.

maltose

A disaccharide composed of two glucose molecules; sometimes called malt sugar. Maltose seldom occurs naturally in foods but is formed whenever long molecules of starch break down.

trehalose

A disaccharide of two glucose molecules, but with a linkage different from maltose. Used as a food additive and sweetener.

hemicelluloses

A group of large polysaccharides in dietary fiber that are fermented more easily than cellulose.

epinephrine

A hormone released in response to stress or sudden danger, epinephrine raises blood glucose levels to ready the body for "fight or flight." Also called adrenaline.

chitin

A long-chain structural polysaccharide of slightly modified glucose. Found in the hard exterior skeletons of insects, crustaceans, and other invertebrates; also occurs in the cell walls of fungi.

glycemic index

A measure of the effect of food on blood glucose levels. It is the ratio of the blood glucose value after eating a particular food to the value after eating the same amount of white bread or glucose.

galactose

A monosaccharide containing six carbons that can be converted into glucose in the body. In foods and living systems, galactose usually is joined with other monosaccharides.

resistant starch

A starch that is not digested.

amylose

A straight-chain polysaccharide composed of glucose units.

cellulose

A straight-chain polysaccharide composed of hundreds of glucose units linked by beta bonds. It is nondigestible by humans and a component of dietary fiber.

pectins

A type of dietary fiber found in fruits.

glycogen

A very large, highly branched polysaccharide composed of multiple glucose units. Sometimes called animal starch, ___ is the primary storage form of glucose in animals.

ketosis

Abnormally high concentration of ketone bodies in body tissues and fluids.

Both starch and fiber are long chains of glucose molecules, but we are unable to digest the bonds between the glucose units in fiber. Therefore, fiber moves through the small intestine undigested while starch is broken down into glucose and absorbed.

Describe the difference between starch and fiber.

A monosaccharide is a single sugar unit (e.g., glucose, fructose, and galactose). A disaccharide (e.g., maltose, sucrose, and lactose) is a molecule of two single sugar units. A polysaccharide (e.g., starch and fiber) is a long chain of sugar units.

Describe the structure of a monosaccharide, disaccharide, and polysaccharide.

dental caries

Destruction of the enamel surface of teeth caused by acids resulting from bacterial breakdown of sugars in the mouth.

gums

Dietary fibers, which contain galactose and other monosaccharides, found between plant cell walls.

complex

Diets high in ___ carbs, including fiber, have been linked to reduced risk of GI disorders, heart disease and cancer.

β-glucans

Functional fiber, consisting of branched polysaccharide chains of glucose, that helps lower blood cholesterol levels. Found in barley and oats.

mucilages

Gelatinous soluble fibers containing galactose, mannose, and other monosaccharides; found in seaweed.

An excessive amount of added sugar probably translates into an excessive amount of calories, and overconsumption of calories leads to weight gain. Overweight and obesity are, in turn, associated with increased risk of chronic disease. Excess sugar intake also increases risk for dental caries.

How does excess amount of carbs affect health?

225/1200 = 18.75% of total calories. 45/100 x 1200 = 540 calories 65/100 x 1200 = 780 calories

In an effort to lose weight, you decide to follow a diet of 1,200 calories with 225 grams of carbohydrate. Calculate the percentage of carbohydrate in this diet and compare this amount to the Daily Value recommendations. Daily Value recommendations for carbohydrate are 300 grams per day. Compare this amount to the recommendation for the overall percentage of carbohydrate, which is 45 to 65 percent of total calories.

condensation

In chemistry, a reaction in which a covalent bond is formed between two molecules by removal of a water molecule.

lignins

Insoluble fibers composed of multi-ring alcohol units that constitute the only noncarbohydrate component of dietary fiber.

functional fiber

Isolated nondigestible carbohydrates, including some manufactured carbohydrates, that have beneficial effects in humans.

ketone bodies

Molecules formed when insufficient carbohydrate is available to completely metabolize fat. Formation of ketone bodies is promoted by a low glucose level and high acetyl CoA level within cells. Acetone, acetoacetate, and beta-hydroxybutyrate are ketone bodies. Beta-hydroxybutyrate is sometimes improperly called a ketone.

sucrose, lactose and maltose

Monosaccharides combine to make disaccharides

glycyrrhizin

Nonnutritive sweetener derived from licorice root. Has a licorice flavor and is 50 to 100 times sweeter than sucrose.

dihydrochalcones (DHCs)

Nonnutritive sweeteners derived from bioflavonoids of citrus fruits. Approximately 300 to 2,000 times sweeter than sucrose and have a licorice aftertaste.

chitosan

Polysaccharide derived from chitin.

insulin

Produced by beta cells in the pancreas, this polypeptide hormone stimulates the uptake of blood glucose into muscle and adipose cells, the synthesis of glycogen in the liver, and various other processes.

oligosaccharides

Short carbohydrate chains composed of 3 to 10 sugar molecules.

pancreatic amylase

Starch-digesting enzyme secreted by the pancreas.

nutritive sweetener

Substances that impart sweetness to foods and that can be absorbed and yield energy in the body. Simple sugars, sugar alcohols, and high-fructose corn syrup are the most common ___ used in food products.

nonutritive sweeteners

Substances that impart sweetness to foods but supply little or no energy to the body; also called artificial sweeteners or alternative sweeteners. They include acesulfame, aspartame, saccharin, and sucralose.

pentoses

Sugar molecules containing five carbon atoms.

simple carbohydrate

Sugars composed of a single sugar molecule (a monosaccharide) or two joined sugar molecules (a disaccharide).

After we eat, our bodies secrete insulin that counteracts a rise in blood glucose by increasing the uptake of glucose by cells. When we have taken in no food for several hours, our bodies secrete glucagon. Glucagon helps maintain glucose levels by stimulating the breakdown of storage glycogen and the release of glucose to the blood.

Which blood glucose regulation hormone is secreted in the recently fed state? The fasting state?

Plant foods are our main dietary sources of carbohydrates. Grains, legumes, and vegetables provide starches and fibers. Fruits provide sugars and fiber. Milk and other dairy products provide sugar in the form of lactose. Sweets and soft drinks contain carbohydrates in the form of sugars.

Which foods contain carbohydrates?

blood glucose levels, rise, insulin & glucagon.

___ ___ ___ (rise/fall) after eating and fall between meals. Two pancreatic hormones, ___ & ___, regulate blood glucose levels, preventing extremely high or low levels.

starch, glycogen and fiber

___, ___ & ___ are long chains (polysaccharides) of glucose units.

Monosaccharides

____ are the building blocks of carbs.

polyols

sorbitol, xylitol, mannitol