Introduction
Common sources
Types of carbohydrates
Common carbohydrate categories
Physiology
Energy Production

Carbohydrates are the predominant source of energy for man.   According to guidelines defined by the U.S. Department of Agriculture (USDA), approximately 60% of your diet should come from carbohydrates.  There are different types of carbohydrates, a fact which becomes important when planning diets for various lifestyles. 

They are produced in plants as their leaves capture rays of sunlight transforming them in a process called photosynthesis.   Thus, any plants bearing edible leaves, stems, fruits, or vegetables are suitable sources of carbohydrate intake.   Additionally, one can easily find carbohydrates in many processed foods such as potato chips, candy bars, and more.

There are two common classifications of carbohydrates, simple and complex.   In orderto fully understand what all this jargon means it is necessary to explain some of the terminology used it is necessary to explain some of the more common terms.   Sacharide literally means "sugar", a mono-saccharide is one sugar, a di-saccharide is two sugars, and a polysaccharide is a chain of sugars linked together.   The body ultimately wants to use the simplest form that it can because this form because this is the form which can most readily be converted into useable energy.   Since complex sugartake longer to become transformed into useable energy, a person who is hypoglycemic or who is undergoing a diabetic crisis will benefit more readily from a simple sugar than a complex one.

Simple Sugars

Monosaccharides: glucose, fructose, and galactose

Disaccharides:  sucrose, lactose, and maltose.   Each sucrose is made up of one glucose and one fructose molecule chemically linked together, each lactose is made up of one galactose and one glucose, and maltose is made up of two glucose molecules.

Complex Sugars

Polysaccharides:  starches, complex carbohydrates.   These include amylose in plants and glycogen in animals.

Dietary Fibers:  Dietary fibers are also polysaccharides but differ from other polysaccharides (such as starch) in that they cannot be broken down by human enzymes.   Though they do not serve as an energy source,  they still play vital bodily functions.   (see Fiber section).  

Once ingested, all carbohydrates, whether they come from potato chips or apples, are turned at least initially into glucose.   This is the easiest energy source for the body to utilize.    When carbohydrates, proteins or fats are present in normal ratios, the body will preferentially utilize carbohydrates.   When they are scarce, fats are burned first.   Lastly, and at the expense of muscles and connective tissues, the body will burn proteins for energy when even fats are scarce.   The thin wasted appearance of chronically starved individuals can be attributed to the removal of proteins from muscle and other connective tissue to supply energy for vital organs.  

When a person consumes more carbohydrates than is biologically needed, blood sugar levels rise, triggering insulin release from the pancreas.    Insulin is considered to be the body’s ‘storage enzyme’ and is responsible for the conversion of glucose to glycogen (the storage form of glucose) which occurs in the liver.   When energy is needed, glycogen can be readily mobilized and converted back to glucose by glucagon, and burned as fuel for the body.   Some of the carbohydrates you eat are utilized right away for energy while other are stored in the form of glycogen.   Since only 2,000 calories (a rough estimate) can be stored as glycogen in your body, excessive calories are stored as fat in adipocytes (fat cells).   

Typically, for each gram (1/28 ounce) of carbohydrate consumed, 4 kcal of energy (Calories) are derived.   Proteins and fats produce 4 and 9 kcal respectively.   Since excessive calories results in obesity (and its associated illnesses) this information is useful since it allows us to calculate our daily caloric intake and compare it to estimated values thought to help maintain proper weight and increase overall health.   To give an idea of what all this means for excessive calories take moderate bicycling.   A typical 114 lb (52 kg) female biking at a moderate pace will burn roughly 145 calories/hour.   With a contribution of 4 kcal/gm of food, it would take approximately 36 grams of carbohydrate to replenish what has been burned.   Above that value will contribute to weight gain.  Below it will contribute to weight loss. 

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