Nutrients are organic and inorganic substances found in food. There are about 50 different nutrients which are normally supplied through the foods we eat. Each nutrient has specific functions in the body. Most natural foods contain more than one nutrient which may be divided into macronutrients, comprising of proteins, fats and carbohydrates and micro nutrients including vitamins and minerals.
Carbohydrates are major components of food and are the main source of energy for the body. Carbohydrates are also essential for the oxidation of fats and for the synthesis of certain non-essential amino acids. They are divided into two types:
Simple Carbohydrates: They are also known as simple sugars including fructose, sucrose and lactose.
Complex carbohydrates: They comprise of a wide variety of fruits as natural sources. They are also comprised of sugars, but the sugar molecules are bound together to form long, more complex chains. They include fiber and starches.
Sources of carbs:
The three main sources of carbohydrates are sugar, starches and cellulose.
Sugars: They comprise of monosaccharides (glucose, fructose and galactose) and disaccharides (sucrose, lactose and maltose). These free sugars are highly water soluble and are easily accumulated. Free sugar along with starches is the key source of energy for the body.
Glucose: It is the most abundantly found sugar in the human body. It is the major source of energy and is present in the blood.
Fructose: It is a major constituent of honey. Average composition of honey is 40% fructose, 30% glucose and 10% sucrose.
Galactose: The term galactose is derived from the Greek word gala meaning milk. Galactose is a constituent of lactose (Milk Sugar) and glycoproteins. Galactose is epimerized to glucose in the liver and is then utilized as fuel.
Sucrose: It is the sweetening agent known as cane sugar. It is found in sugarcane and various fruits. The enzyme producing hydrolysis of sucrose is called sucrase or invertase. Honey contains invert sugar which is sweeter than sucrose.
Lactose: It is the sugar present in milk. It is a reducing disaccharide.
Maltose: It is a reducing disaccharide and is a product of the action of amylase (saliva or pancreatic juice upon salt).
Starch: It is the reserved carbohydrate of the plant kingdom and is present abundantly in potatoes, tapioca, rice, wheat and other foods.
Cellulose: It is the indigestible component of carbohydrates with little nutritional value and contributes to dietary fiber. It is the chief carbohydrate in plants and constitutes 90% of cotton, 50 % of wood and 40 % of straw. It is the most abundant organic material in nature. It cannot be digested in the human body and is used in a variety of commercial applications in the form of raw material used in the production of synthetic fibers, celluloids, nitrocellulose and plastics.
Glycogen: It is a reserve carbohydrate in animals. It is stored in the liver and muscles. About 5% of the total weight of the liver is made up of glycogen. If the dietary carbohydrates are unable to meet the energy needs of the body, protein and glycerol from dietary and endogenous sources are used by the body to maintain glucose homeostasis.
Dietary Fiber: This non-starch polysaccharide is a physiologically important component of the diet. It is found in vegetables, fruits and greens. It can be divided into cellulose and non-cellulose polysaccharides like insulin, plant gums and mucilages. The role of dietary fiber has attracted considerable attention during the last few years. Fiber absorbs water, reduces constipation and encourages bowel movements. It is also known for its cholesterol-lowering effect on the human body. Fiber also plays a crucial role in the process of weight reduction. Certain studies also indicate that it helps in the elimination of gall stones, diabetes, hypertension, coronary heart disease, bowel disease and cancer.
Carbohydrates are the most important energy source of the body for most tissues. Brain cells derive their energy mainly from glucose. In strenuous exercise, when muscle tissue is unable to get enough oxygen, anaerobic glycolysis forms the major source of energy for muscles.
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