Chapter 5

Carbohydrates: The Preferred Body Fuel

Carbohydrates

Essential nutrientBody’s main source of energySugar, Starches, FiberNearly all sources are plant sourcesCarbon, 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