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Balanced Diet for Humans - Sources and Functions

Published on Aug 18, 2022 and last reviewed on Feb 06, 2023   -  7 min read


A balanced diet includes all the essential nutrients required by human beings. Read this article to learn about its sources and utilization in the body.

What Is a Balanced Diet?

Food is one of the most vital requirements for any living organism, and humans are no exception. Every body cell, tissue, and organ needs food to maintain a healthy state. Fair amounts of the right food types should be consumed to remain healthy, which is considered a balanced diet.

What Is the Function of Food in Our Body?

Human beings need food for growth, maintenance, and repair. And various nutrients are used by body cells for the following functions:

  1. Growth and repair of body tissues, muscles, bones, teeth, and skin.

  2. Energy for cell metabolism.

  3. Protection from disease and infection.

  4. Maintenance of chemical composition of cells.

A person who eats too little may become weak and thin as his tissues are used as a source of energy; growth and repair processes slow down so that wounds fail to heal correctly, and the body loses its ability to fight diseases.

On the other hand, if a person overeats, his body is inflated with stored food. This state is called obesity and may result in damage to the heart and the circulatory system.

Finally, if someone eats only a moderate amount of food but of the wrong type to suit body requirements, he may suffer from deficiency diseases such as anemia, scurvy, beriberi, etc.

What Are the Essential Components of a Balanced Diet?

The essential components of a balanced diet include -

  • Sufficient amount of energy.

  • Correct proportions of carbohydrates, proteins, and fats.

  • Mineral salts.

  • Vitamins.

  • Water.

  • Roughage.

What Are Carbohydrates and Their Types?

The principal carbohydrate for the human body is glucose. Glycogen and blood sugar glucose are carbohydrates of animal origin. Cellulose is a less familiar carbohydrate that herbivores can only digest and is available to carnivores and omnivores only when they eat herbivores.

The most familiar carbohydrates are sucrose and starch.

  • Sucrose-containing foods include sweet fruits, honey, jam, and treacle.

  • Starchy foods include bread, potatoes, rice, and spaghetti.

There are three types of carbohydrates -

  1. Monosaccharides.

  2. Disaccharides.

  3. Polysaccharides.


The simple sugar unit with the variation of carbon from three to seven is known as monosaccharides. There are five types of monosaccharides -

  1. Triose (glyceraldehyde).

  2. Tetrose.

  3. Pentose (ribose - C5H10O5 and deoxyribose - C5H10O4).

  4. Hexose (glucose and fructose).

  5. Heptose.

All monosaccharides are reducing sugars and are readily soluble in water.


The combination of two monosaccharides by a glycosidic bond is known as disaccharides. Some disaccharides are reducing sugars and are soluble in water (maltose), and some are non-reducing sugars and are insoluble in water (sucrose).

The three significant disaccharides are -

  1. Maltose = glucose + glucose (digestive enzyme - maltase).

  2. Lactose = glucose + galactose (digestive enzyme - lactase [deficient in the old]).

  3. Sucrose = glucose + fructose (digestive enzyme - sucrase).

When two glucose units are linked, maltose is formed by releasing one water molecule.


The combination of numerous glucose units by glycosidic bonds is known as a polysaccharide. The three main polysaccharides are starch, glycogen, and cellulose. All polysaccharides are non-reducing sugars, and they are rarely soluble in water.

  • Starch: This is the form of carbohydrate stored in the plant kingdom. The starch molecule contains the main chain (amylose) and the branching chain (amylopectin). During digestion, starch is hydrolyzed by amylase enzymes into maltose and dextrose, which are then converted into glucose by maltase and dextrose enzymes, respectively.

  • Glycogen: This is the form of carbohydrate stored in the human body. Glycogen has only amylopectin and no amylose.

  • Cellulose: Cellulose is the most abundant organic compound in the biosphere. It is the polymer of thousands of glucose units and can only be digested by herbivores. Cellulose has only amylose and no amylopectin.

What Are the Functions of Carbohydrates?

  • Carbohydrates serve as sources of energy and act as metabolic intermediates.

  • Starch in plants and glycogen in animals are polysaccharides that can be rapidly mobilized to yield glucose.

  • One gram of carbohydrate can produce up to 17 kJ of energy. Most carbohydrates are converted into glucose before being used for metabolism. ATP (adenosine triphosphate), the universal currency of free energy, is a phosphorylated glucose sugar derivative.

  • Carbohydrates are essential food reserves. Excess carbohydrates can be converted into glycogen and stored in the liver and muscles. The body can store only a limited amount of carbohydrates in this way. When this limit has been reached, any more carbohydrate is converted into fats and oils and stored in particular tissues.

  • Ribose and deoxyribose sugars are the partial structural framework of DNA & RNA.

  • Polysaccharides are the structural elements in the cell wall of bacteria and plants and the exoskeleton of arthropods. Cellulose is the main constituent of plant cell walls and is the most abundant organic compound in the biosphere.

  • Carbohydrates are linked with many proteins (glycoproteins) and lipids (glycolipids).

Although, a high daily sucrose intake can cause tooth decay, heart disease, and obesity. A rise in blood sugar above its normal limit can also cause diabetes.

What Are Lipids and Their Functions?

Fats and oils are together known as lipids. Oils are fatty acids that are liquids at 20 °C, while fats are in solid or semi-solid form at that temperature.

Lipids are also known as triglycerides. They have three glyceraldehydes (CH2OH) that can link with three fatty acids. Lipids can be of animal origin (butter, lard, meat, and fish) or plant origin (nuts, seeds, margarine, and cooking oils). Lipids are obtained mainly from plant sources. They contain essential fatty acids that cannot be made in the human body and play an important part in metabolism.

Lipids are an essential source of energy. Sunflower, soya bean, and cooking oils are rich in essential fatty acids. One gram of fat or oil can produce up to 38 kJ of energy.

Functions of Lipids -

Lipids are essential components of the body. They are present in 10 % to 15 % of the body weight and form part of the lipoprotein cell membrane or plasmalemma. The main functions of lipids are stated below -

  • Lipids are concentrated energy reserves and are needed for the growth, maintenance, and reproductive efficiency of the body.

  • The skin fat depot is responsible for the insulation of body heat.

  • Lipids protect specific organs (such as kidneys) by surrounding them.

  • Vitamins A, D, E, and K are associated with lipid-containing foods.

  • Lipids can be used to add extra flavor to foods.

Irrespective of that, animal origin lipids contain cholesterol, which is not present in plant origin lipids. Cholesterol is formed in the human liver and circulates in the bloodstream. Excess cholesterol is deposited in the blood vessels, and these deposits may block the coronary artery.

What Are Proteins and Their Functions?

Proteins are combinations of many amino acids linked by peptide bonds. In total, there are around 10000 proteins that are formed by synthesizing around 26 amino acids. There are dipeptide, tripeptide, and polypeptide proteins.

The human body is composed of 12 % to 18 % of proteins. Proteins are present mainly in the muscles, bones, and skin. They also form part of the lipoprotein of cell membranes and the nucleoprotein of cell nuclei. And the deficiency of proteins in malnourished small children can lead to a disorder known as Kwashiorkor. This causes a distended stomach, muscle wasting, anemia, and liver and pancreas degeneration.

Proteins differ in various living organisms. For example, plant proteins differ from animal proteins, and human proteins differ from cow proteins.

Animal origin proteins include:

  • Meat

  • Fish.

  • Eggs.

  • Milk.

  • Cheese.

Plant origin proteins include:

  • Bread.

  • Cereals.

  • Potatoes.

  • Beans.

  • Peas.

Animal proteins can supply all the essential amino acids known as high biological value (HBV) or first-class proteins. Plant proteins do not have all the essential amino acids, which is why they are known as low biological value (LBV) or second-class proteins.

Plants can make all their essential proteins themselves. A human being can make their proteins and must have certain essential amino acids in his cells, which will come from the protein foods he eats. The essential amino acids necessary for humans are:

  • Arginine.

  • Cysteine.

  • Isoleucine.

  • Leucine.

  • Histidine.

  • Lysine.

  • Methionine.

  • Phenylalanine.

  • Threonine.

  • Tryptophan.

  • Tyrosine.

  • Valine.

Functions of Proteins -

  • Proteins are essential for growth, repair, and replacement. They are necessary for growing children, pregnant mothers, and people recovering from sickness.

  • Structural proteins are needed to build new, repair, and replace damaged muscles, bones, and skin tissues.

  • Functional proteins, enzymes, hormones, and blood components are essential for cell metabolism.

  • Proteins are not essentially used as energy sources, although they can produce up to 17 kJ per gram.


A balanced diet and a healthy lifestyle are essential for good health and well being. A balanced diet ensures a healthy immune system thereby protecting the body from various acquired diseases. Thus incorporating healthy changes in diet would not only enhance the nutritional value but also prevent illness.

Last reviewed at:
06 Feb 2023  -  7 min read




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