Carbohydrates

Chapter

4

Carbohydrates

• Carbohydrates are organic compounds that contain carbon (C), hydrogen (H), and Oxygen (O) in the ratio of 1 carbon atom and 1 oxygen atom for every 2 hydrogen atoms.

• The sugar glucose contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.• C6H12O6

Carbohydrates

• Two or more sugar molecules can be assembled to form increasingly complex carbohydrates.

• The two main carbohydrates found in food are simple carbohydrates (sugars) and complex carbohydrates (starches and dietary fiber).

Simple Sugars: Monosaccharides and Disaccharides

• Simple carbohydrates are naturally present as simple sugars in fruits, milk, and other foods.

• Plant carbohydrates can be refined to produce sugar products like table sugar and corn syrup.

Simple Sugars: Monosaccharides and Disaccharides

• The two main types of sugars are monosaccharides and disaccharides.

• Monosaccharides consist of a single sugar molecule (“mono” meaning one and “saccharide” meaning sugar).

• Disaccharides consist of two sugars chemically joined (“di” meaning two).

Monosaccharides

• The most common monosaccharides in the human diet are glucose, galactose, and fructose.

Monosaccharides: The Single Sugars

• Glucose• Found in fruits, vegetables, honey• “Blood sugar”—used for energy• Virtually the only fuel used by the brain.• It is the most abundant simple carbohydrate

found in nature.• It makes up at least 1 of the 2 sugar molecules

in every disacharide.

Monosaccharides: The Single Sugars

• Fructose• Found in fruits, honey, corn syrup• Also called levulose or “Fruit sugar”• Fructose tastes the sweetest of all sugars• Used as a sweetener in foods

Monosaccharides: The Single Sugars

• Galactose• Found as part of lactose in milk• Rarely occurs as a monosaccharide in food• Chemically bonded to glucose to make lactose

Disaccharides: The Double Sugars

• Disaccharides—two linked sugar units• Sucrose: glucose + fructose

• “Table sugar”• Made from sugar cane and sugar beets• When a label lists sugar as an ingredient, it is referring

to sucrose.

Disaccharides: The Double Sugars

• Lactose: glucose + galactose• “Milk sugar”• Found in milk and dairy products

Disaccharides: The Double Sugars

• Maltose: glucose + glucose• Found in germinating cereal grains• Product of starch breakdown• Maltose is fermented in the production of beer

Joining and Cleaving Sugar Molecules

Complex Carbohydrates

• Complex carbohydrates are chains of more than two sugar molecules.

• Short chains may have as few as three monosaccharide molecules.

• Long chains (polysaccharides) can have hundreds or even thousands.

Complex Carbohydrates

• Starch• Long chains of glucose units

• Amylose–straight chains• Amylopectin–branched chains

• Found in grains, vegetables, legumes

Complex Carbohydrates

• Glycogen• Highly branched chains of glucose units• Body’s storage form of carbohydrate

Oligosaccharides

• Oligosaccharides are short carbohydrate chains of 3 to 10 sugar molecules.

• Dried beans, peas, and lentils contain the two most common ones: raffinose and stachyose.

Oligosaccharides

• Human milk contains more than 100 different oligosaccharides.

• Some bind to bacteria to help them pass.• Some serve as dietary fiber.• Some assist in brain development.

Polysaccharides

• Polysaccharides are long carbohydrate chains.

Polysaccharides

• Some form straight chains, while others branch off in all directions.

• Their configuration makes them either digestible (starch) or indigestible (dietary fiber).

Starch

• Plants store energy as starch.

• Dietary sources of starch:• Grains such as wheat, rice, corn, oats,

millet, and barley.• Legumes such as peas, beans, and lentils.• Tubers such as potatoes, yams, and

cassava.

Glycogen

• Animals store carbohydrates in the form of glycogen.

• It is also called animal starch.

Glycogen

• Glycogen consists of highly branched chains of glucose.

• Glycogen is stored largely in the skeletal muscle and liver.

Complex Carbohydrates: Fiber• Dietary + Functional = Total Fiber• Indigestible chains of monosaccharides

• Nonstarch polysaccharides: long chains• Cellulose, hemicellulose, pectins, gums, mucilages• Lignins

• Found in fruits, vegetables,

grains, legumes

Dietary Fiber

• Soluble fibers dissolve in water.

• Insoluble fibers do not dissolve in water.

• Soluble fiber from psyllium and oats has been shown to lower blood cholesterol levels.

Sources of Dietary Fiber

• Only plant foods contain dietary fiber.

• Soluble fiber is found in oat bran, legumes, soybean, and some fruits and vegetables.

• Insoluble fiber is found in wheat bran and most whole grains.

Carbohydrate Digestion and Absorption

• Mouth• Salivary amylase begins digestion of starch

• Small intestine• Pancreatic amylase completes starch digestion• Brush border enzymes digest disaccharides

• End products of carbohydrate digestion• Glucose, fructose, galactose• Absorbed into bloodstream

• Fibers are not digested, are excreted in feces

Carbohydrates in the Body

• Functions of glucose• Energy source• Spares body protein• Prevents ketosis• Excess stored as glycogen

• In liver and muscle

Carbohydrates in the Body: Regulating Blood Glucose

Carbohydrates in the Diet

• Recommended carbohydrate intake• AMDR = 45–65% of calories• Daily Value (for 2,000 kcal) = 300 grams• Dietary Guidelines

• Variety of grains, fruits, vegetables• Moderate sugar intake

• Current consumption

Carbohydrates in the Diet

• Increasing complex carbohydrate intake• Grains,

especially whole grains

• Legumes• Vegetables

Whole Kernels

• Germ – the innermost part. Can grow into a new plant. Rich in protein, oils, vitamins, and minerals.

• Endosperm – largest middle portion. High in starch.

Whole Kernels

• Bran – protective coating. Dietary fibers.

• Husk – inedible covering. Also called chaff.

Refined Grains

• When grains are refined, the process removes the outer husk and bran layers. It sometimes also removes the inner germ of the grain kernel.

Refined Grains

• This is done when making white flour from wheat and making white rice from brown.

Carbohydrates in the Diet

• Moderating sugar intake• Use less added sugar• Limit soft drinks, sugary cereals,

candy• Choose fresh fruits or those canned

in water or juice

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Carbohydrates in the Diet

• Nutritive Sweeteners• Natural v. refined• Sugar alcohols

• Artificial Sweeteners• Saccharin• Aspartame• Acesulfame K• Sucralose

Carbohydrates and Health

• High sugar intake• Low-nutrient content• Contributes to tooth decay• If excess kcal, contributes to obesity

• High fiber intake• Better control of blood glucose• Possible reduced cancer risk• Reduced risk of heart disease• Healthier gastrointestinal functioning

An Apple a Day…

• The old adage, “An apple a day keeps the doctor away” has persisted over time due to actual health benefits from apples.

• Apples have a high pectin content, a soluble fiber known to be an effective GI regulator.

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Cellulose

• Cellulose forms the nondigestible, fibrous component of plants.

• It is part of grasses, trees, fruits, and vegetables.

Increasing Fiber Intake

• To increase your fiber intake, eat more breads, cereals, pasta, rice, fruits, vegetables, and legumes.

• Eat fruits and vegetables with the peel, if possible, as this is high in fiber.

• Add fruit to muffins and pancakes.• Add legumes, such as lentils and pinto, navy,

kidney, and black beans to casseroles.

ADA Position on Nutritive and Non-Nutritive Sweeteners

• It is the position of the American Dietetic Association that consumers can safely enjoy a range of nutritive and non-nutritive sweeteners when consumed in a diet that is guided by current federal nutrition recommendations, such as the Dietary Guidelines for Americans, and the Dietary References Intakes, as well as individual health goals.

Sugar and Children’s Behavior

• In a study designed to determine whether or not sugar truly affects a child’s behavior, the results indicated that dietary sugar does not cause adverse behavior.

Photo © Eric Gevaert/ShutterStock, Inc.

Dental Health

• Good dental hygiene, adequate fluoride, and proper nutrition help maintain healthy teeth.

• A well-balanced diet contains vitamins and minerals crucial for healthy bones and teeth.

• To help prevent dental caries, avoid continuous snacking on high-sugar foods.

ADA Position on Health Implications of Dietary Fiber

• It is the position of the American Dietetic Association (ADA) that the public should consume adequate amounts of dietary fiber in the form of plant foods.

Effects of Excess Fiber

• With all of its health advantages, high fiber intake can cause problems, especially in those who drastically increase their fiber intake in a short period of time.

• A sudden increase in fiber can cause increased intestinal gas and bloating.

• If you increase your fiber intake, you should also increase your water intake to prevent constipation.

Total Fiber

• Dietary fiber consists of nondigestible carbohydrates and lignin that are intact and intrinsic in plants.

• Functional fiber refers to isolated, nondigestible carbohydrates that have beneficial physiological effects in humans.

• Total fiber is the sum of dietary fiber and functional fiber.

Babies and Honey

• Because honey and Karo syrup may contain spores of the bacterium Clostridium botulinum (botulism), they should never be fed to infants younger than one year of age.

• Infants do not produce as much stomach acid as older children and adults, which can allow the spores to germinate in the GI tract.

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