Chapter 4 – Carbohydrates: Sugar, Starches, and Fiber

Carbohydrates
– A large class of nutrients, including sugars, starch, and fiber, that function as the body’s
primary source of energy.

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
} 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
} 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: (simple carbohydrate)
◦ 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. (combinations of
simple carbohydrate)
◦ Glucose + fructose = sucrose (table sugar)
◦ Glucose + glucose = maltose (sugar in grains)
◦ Glucose + galactose = lactose (milk sugar)

Polysaccharides Are Complex Carbohydrates

} Polysaccharides are long chains of monosaccharides linked together.
} Three groups:
◦ Starch
◦ Fiber
◦ Glycogen
} Polysaccharides are long chains of many glucose units joined together in a straight
chain or with branches.
} Starch is stored in plants.
o Consists of many glucose units strung in a chain
o May be straight or branched chains
o Found in pasta, rice, bread, and potatoes
} Fiber is not digestible, but is important.
o Dietary fiber: found naturally in foods
o Functional fiber: added for a beneficial effect
o 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
o 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
} Glycogen is stored in animals.
o The form of glucose stored in the liver and muscle cells of humans and
animals
o Can be an important source of glucose for the cells of the body
o Breaks down when the animal dies and is not available in meat or poultry
consumed

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)
} 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.

Some People Cannot Digest Milk Sugar

} Lactose Maldigestion Develops with Aging
} Severe Lactase Deficiency Produces Lactose Intolerance
Lactose Maldigestion Develops with Aging
} Lactose maldigestion
◦ 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
} 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

1. Insulin Regulates Glucose in Your Blood

– Hormones are chemical messengers that regulate important conditions in the body.
o 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
 o Carbohydrate-rich meals increase blood glucose.
o Elevated blood glucose triggers release of insulin.
o Glucose can be stored as glycogen in the liver and muscle cells or as fat.

2. Carbohydrates Fuel Your Body between Meals

} When blood glucose levels drop, your body calls on its glycogen reserves.
} Glucagon: a peptide 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 non-carbohydrate 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

3. 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.

IMPORTANT NOTES TO REMEMBER:

1. Glucose, fructose, and galactose are simple carbohydrates. Glucose is the preferred
fuel for the brain and red blood cells.
2. Two monosaccharides are joined to form disaccharides. Sucrose (table sugar), lactose
(milk sugar), and maltose are examples of disaccharides.
3. Many glucose units are joined together to form polysaccharides. Glycogen (found in
animal tissue), starch (found in plants), and fiber are examples of polysaccharides.
4. Lactose maldigestion is the inability to properly absorb the milk sugar lactose because
of a reduced amount of the enzyme lactase.
5. 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.