5. DIETARY FIBRE
Carbohydrates form the main source of calories in the diet of all people. Composed of carbon, hydrogen and oxygen, carbohydrates include simple sugars and combinations of simple sugars such as starch and glycogen. Non-digestible, bulk-providing fibres are also carbohydrates but the human body lacks the enzymes necessary to turn these fibres into simple sugars.
The simple sugars in our diet include glucose, fructose and galactose. The sugars, sucrose (cane and beet sugar, honey, maple sugar), lactose (milk sugar) and maltose (malt sugar) are combinations of two simple sugars. Sucrose = glucose + fructose; lactose = glucose + galactose: maltose = glucose + glucose. Many glucose molecules hooked together (polymers), varying in size from a few glucose units (malts, dextrin) to thousands of glucose units (starch, glycogen, cellulose), are also important in nutrition.
Those that the human body can digest (starch and glycogen) are important sources of energy. Indigestible forms such as cellulose pass through the intestinal tract undigested, but provide bulk or “roughage”, that prevents constipation, keeps the intestinal tract from developing toxic materials, keeps digestive tract contents moving (enhances peristaltic activity) and keeps our bowls clean and healthy. Glycogen, a carbohydrate known as “animal starch”, is made and stored in our liver and skeletal muscles as a source of readily available energy to draw on during prolonged physical activity.
Glucose is the body’s most important energy-providing molecule — a clean burning fuel for all life
functions that require energy, from molecular biochemistry to athletic performance.
The blood continuously delivers glucose to all tissues. The brain uses glucose almost exclusively for its energy requirements. It cannot burn fats or proteins. A brain shortage of glucose results in the behavioural symptoms of low blood sugar (hypoglycaemia), which are really symptoms of low brain sugar.
Glucose and insulin
The hormone insulin regulates the metabolism of glucose, starch, glycogen, sucrose, lactose and maltose - the digestible carbohydrates that contain glucose. Insulin increases the rate at which glucose is transferred from the blood into cells. Through this action, insulin regulates all processes in which glucose plays a part. Insulin requires the minerals chromium and zinc to fulfill its functions. Zinc and chromium deficiency make insulin action inefficient, resulting in chronic high blood sugar (hyperglycemias) or diabetes.
Sugars such as fructose do not need insulin for transport into cells, nor for the initial steps of their
metabolism. Fructose may be preferable to glucose for certain purposes, although it has problems of its own.