Chapter 5
Carbohydrates: The
Preferred Body Fuel
Carbohydrates
Essential nutrient
 Body’s main source of energy
 Sugar, Starches, Fiber
 Nearly all sources are plant sources
 Carbon, hydrogen and oxygen bonded to
form saccharides

TYPES OF CARBOHYDRATES
Monosaccharides, Disaccharides and
Polysaccharides
Monosaccharides – composed of single
sugar units
 - the smallest carbohydrate molecule
MONOSACCHARIDES

1. Glucose
- blood sugar
 - Circulates in the bloodstream
 - the body’s source of energy

MONOSACCARIDES

2. Fructose
- sweetest tasting of the sugars
 - occurs naturally in fruits and honey

MONOSACCHARIDES

3. Galactose
- doesn’t occur alone
 - bonded to glucose to form lactose; milk
sugar

DISACCHARIDES

-Made up of two sugar units; must be
split during digestion to form
monosaccharides

1. Sucrose – sugar as additives
(1 glucose+ 1 fructose)

Ex. Beet sugar, sugar cane, molasses,
maple syrup
DISACCHARIDES

2. Lactose – milk sugar

(1 glucose + 1 galactose bonded together)
3. Maltose – (2 glucose, bonded together)
- formed during digestion of starch;
-found in some grains such as malt
POLYSACCHARIDES

- Carbohydrates made up of many sugar
units that must be broken down during
digestion; starches and fiber
POLYSACCHARIDES
1.Starches
– the storage form of energy in plants
 - many glucose molecules bonded together
 - grain products

POLYSACCHARIDES

2. Dietary Fiber
-tough fibrous cell walls of plants
 - found only in plant foods
 - enzymes can’t digest fiber but bacteria in
the digestive track can break down some
fiber
 - little to no energy (calories) provided by
fiber


SIMPLE CARBOHYDRATES

- Mono and Disaccharides (sugars)
COMPLEX CARBOHYDRATES
- Polysaccharides due to complex molecular
structure (starches and fiber)
FUNCTIONS OF CARBS

1. Provide Energy – preferred source
because the body can use them most
efficiently

2. Spare Proteins – protein is used for
energy when carbs are unavailable but
used less efficiently; proteins primary
function is to build and maintain cells
FUNCTIONS OF CARBS

3. Break Down Fats – body can’t
completely break down fats if diet is too
low in carbs -ketone bodies blood
may become too acidic ketosis
(damages cells and organs, nausea,
weakness) coma and death
FUNCTIONS OF CARBS
4. Provides Bulk in the Diet – promotes
normal digestion and elimination of
wastes
 -feel full sooner
 -slower to leave the stomach so feel full
longer
 -usually lower in calories

FUNCTION OF CARBS

Dietary Fiber
- Soluble Fiber – can dissolve in water and
develops a gel-like consistency; ex. Oat
bran, legumes, apple and citrus pectin
 - Insoluble Fiber – does not dissolve in
water; associated with reducing cancer
risks; ex. wheat bran, whole grain
Functional Fiber – taken from plants,
developed in labs- added to processed
foods to provide health benefits

How Your Body Uses Carbs

- Carbs must be converted to glucose
for cells to use them as energy source

- Poly’s and Di’s are broken down into
Mono’s which are small enough to move
through the intestinal wall into the
bloodstream
Using Carbs

Mono’s travel to the liver where fructose
and galactose are converted into glucose
Using Carbs

Blood sugars rise hormone called
insulin is released to help lower glucose
levels by burning glucose for energy

Hormone – chemicals produced in the
body and released into the blood stream
to regulate specific body processes
Using Carbs
If there is no immediate energy needs
the glucose is stored as glycogen;
 2/3 of glycogen is stored in the muscles,
1/3 stored in the liver

-the liver can store limited amount;
excess is stored as fat
 -fat stores cannot be converted back to
glucose
