UNIT 3 - Macro nutrients (Carbohydrates)

Introduction

• Food is composed of three main constituents, namely, carbohydrates, proteins, fats and their derivatives.
• In addition these constituents , inorganic mineral elements and diverse organic compounds such as vitamins, pigments, enzymes and acids are also present.
• The variation in structure, texture, colour, flavor and nutritive value is because of the varying proportions and arrangement of these constituents.
• Knowledge of these constituents, their properties and reactions with other constituents is necessary for a person who processes, severs and stores food.

What are Carbohydrates?

• Carbohydrates are an important group of nutrients. It is present in various forms in the foods we cook, processed food which we purchase and forms the bulk of our diet.
• They are mainly present in food in the form of sugars, starches and fibers. They are organic compounds made up of C, H &. O
• They are called carbohydrates because H & O are present in the same proportion as found in water i.e. 2:1.
• They are processed in plants by the process of photosynthesis.
• Chlorophyll is a green pigment which absorbs energy from sunlight and enables plants to build up carbohydrates from CO2 and H20.
• Glucose cannot be stored on a large scale so it is converted to starch with the removal of water and is stored in various parts of the plant. E.g. in cereal grains and potatoes CHO is stored as  starch.
•  In bananas, mango and sugar beets it is stored as sugar.
• Tender green peas and maize contain carbohydrate in the form of sugar which is converted into starch as the seed matures.
•  However the reverse is seen in the fruits, immature fruits contain starch which is converted into sugar as the fruit ripens.
• The various parts of the plant where CHO is stored form the main source of CHO in diet.

Classification of DIETARY Carbohydrates

Carbohydrates, which are of importance in the diet, are classified on the basis of the number of sugar units present in them. They may also be classified as follows:

Available Carbohydrates - which are digested in the human body and yield energy when they are oxidized in the body.
Unavailable Carbohydrates – which cannot be digested because the human body does not contain the enzymes necessary for their breakdown. They do not provide any energy to the body but are necessary as they perform some important functions in the body such as regular elimination of faecal waste

Classification of Carbohydrates

Classification of Carbohydrates

Functions of Carbohydrates

Role of carbohydrates in the human diet is to supply energy. It should always be kept in mind that carbohydrates or calories alone cannot adequately supply our energy needs, for we must have our carbohydrates in combination with other needs, such as proteins, water, vitamins, minerals, fats, etc.

• Carbohydrates Supply Energy

The body uses carbohydrates directly from the monosaccharide glucose. Glucose is in the blood and extracellular fluids and can be made from glycogen. Glycogen is stored in the liver and muscles and in smaller amounts in the other organs and tissues of the body. Energy is derived from glucose by the splitting of the glucose molecules into smaller compounds and oxidizing these to form water, which frees quite a large amount of energy.

• Carbohydrates Provide Fuel for the Central Nervous System

Nerve cells are very dependent upon glucose for their functioning.
Carbohydrates Provide Fuel for the Muscular System
Carbohydrates provide the major fuel for muscular exercise. Fats and proteins can be used only indirectly—by first being converted into carbohydrates. For this reason, a proper diet should consist primarily of carbohydrates—not primarily of proteins

• Carbohydrates Supposedly Spare Proteins

 Carbohydrates also spare proteins from being broken down for energy so that they can perform their main role of building body.

• Carbohydrates Supposedly Supply “Dietary Fiber”

“Dietary fiber” is a fairly new term coined to describe the cellulose inside plant cells. Cellulose is known to be indigestible by humans, though it is digested and used for energy by herbivores. The claims made about “the beneficial role of dietary fiber in preventing diseases” are so popular and so widely made that they are practically accepted as fact.

Significance of Dietary fiber (Prevention/Treatment of Diseases)

• Dietary fiber refers to the total amount of naturally occurring material in plant foods, which is not digested.
• The terms roughage, bulk, and unavailable polysaccharides are synonymous with fiber.
• Fibers cannot be digested by human enzymes.
• Dietary fiber or roughage does not provide humans with but performs many important functions in the body.
• Fiber can absorb and hold water thereby increasing faecal bulk.
• This acts as a laxative and reduces intraluminal pressure in the colon preventing diverticulosis.
• Insoluble fiber prevents constipation by stimulating peristalsis in the large intestine.
• The contraction of muscular walls of the digestive tract is stimulated by fiber.
• Fiber increases water absorption, forming a larger, softer stool that rapidly passes through the colon.
• Soluble fiber binds bile acids and cholesterol and is beneficial to people suffering from coronary heart disease.
• Fiber reduces the triglyceride and cholesterol levels in blood.
• Fiber is beneficial to people on weight reduction regime. It helps in lowering blood sugar levels in diabetic individuals by slowing down carbohydrate absorption and lowers the insulin requirement. Regular intake of fiber may prevent cancers of the colon and rectum. Food such as whole grain cereals, fruits, and vegetables, especially when the peel and seeds are edible, are rich sources of fiber. The fiber content of the daily diet should be approximately 30-40 g/day.

Functions and sources of dietary fiber

Insoluble Fibers

Soluble fibers

Recommended Dietary/daily Allowance

Deficiency of carbohydrates

• The daily diet should not contain less than 100 grams of carbohydrates
• Carbohydrate deficiency is uncommon in our country as diets are cereal based.
• A deficiency in carbohydrates in the diet results in utilization of fats for energy.
• In severe deficiency, incomplete oxidation of fats causes ketone to accumulate in the blood.
• excess of carbohydrates

Excess of Carbohydrates

• Excessive consumption of refined sugars could be one of the causes of tooth decay.
• Excessive sugar depresses the appetite, provides hollow calories and could result in malnutrition.
• High intake of sugar and refined carbohydrates increases the blood triglyceride levels leading to heart diseases.
• When excessive carbohydrates are consumed they are converted into fat which are stored in the adipose tissue which could lead to obesity.
• Excessive fiber can irritate the intestinal lining causing cramps and bloating due o gas formation.
• Excessive fiber interferes with the absorption and availability of mineral elements such as iron and calcium.

Sources of Carbohydrates

CONCLUSION

• Carbohydrates are the nutrients that form the bulk of our diet.
• They include sugars, starch and fiber and occur abundantly in the plant kingdom.
• They are made up of carbon, hydrogen and oxygen.
• Carbohydrates are an essential nutrient and a minimum quantity should be consumed daily.
• The diet should not provide more than 70 % energy from carbohydrates and at least 25 – 30 g fiber should be consumed daily.
• Excess intake of carbohydrates should be avoided.