Part 1: Carbohydrates - Kind and Sources

Except for lactose and a small amount of glycogen from animal origin, plants provide the carbohydrate source in human diet.

Monosaccharides
1) Glucose - forms naturally in food or in the body through digestion of more complex carbohydrates. The liver can also make glucose from amino acids etc.

2) Fructose - occurs in fruits and honey. Converts to glucose in the liver.

3) Galactose - does not exist freely in nature; it combines with glucose to form milk sugar in mammary glands.

Oligosaccharides
2-10 monosaccharides form together and bond chemically.

1) Sucrose - (glucose+fructose) or table sugar. Occurs in sugar cane, honey, maple syrup & brown sugar.

2) Lactose - (glucose+galactose). Found in milk and milk sugar

3) Maltose - (glucose+glucose). Found in beer, breakfast cereals and germinating seeds.


Polysaccharides

Linkage of 3 to thousands of sugar molecules. Formed by dehydration. Commonly reffered to as complex carbohydrate it is the most important dietary source of carbohydrate (accounts for 50% of carbo intake).

PLANT SOURCES
1)Starch - storage form of carbohydrates in plants, occurs in seeds, rice, corn and various grains of bread, cereal, pasta and pastries. Large amount also in peas, beans, potatoes and roots.

2) Fiber - nonstarch, structural polyssacharide. Fiber resist breakdown by human digestive enzymes although a small portion ferments by action of intestinal bacteria. Fiber exist exclusively in plants; they make up the structure of leaves, stems, roots, seeds and fruit coverings.
-Water soluble fiber (lowers cholesterol) - psyllium husk, B-glucan, pectin & guar gum present in oats, beans, brown rice, peas, carrot, corn husk and many fruits.
-Water insoluble (scrapes and cleans intestine)- cellulose, hemicellulose and lignin and cellulose-rich products (wheat bran).

ANIMAL POLYSACCHARIDE
Glycogen, the storage carbohydrate peculiar to mammalian muscles and liver. It is stored by binding many glucose molecules together by a process called glucogenesis.

Note: a well-nourished 80kg person stores approximately 500grams of carbohydrate. Of this, muscles glycogen accounts for 400 grams, followed by 90-110 grams as liver glycogen with 2-3grams in blood as glucose.

Each gram of either glycogen or glucose contains 4 calories(Kcal) of energy, the person stores 1500-2000 kcal as carbohydrate - enough energy to power a 20 mile run at high intensity.

During exercise, the glycogen in the muscles (intramuscular glycogen) provide most of the energy for active muscles. The glycogen in the liver breaks down into glucose for other extramuscular metabolic functions.