The amount of energy to be provided by a balanced diet for any person will depend on several factors: age, sex, body size, lifestyle, occupation, and the climate of the area he is in. The proportion of the various food classes in a diet is also not the same for different persons, due to varying physical and physiological requirements..
A balanced diet is an optimal combination of all the basis classes of foods – carbohydrates, proteins, fats, vitamins, minerals, fibers and water – taken in sufficient quantities and in the correct proportion.
It has the following functions: a) provide sufficient energy to maintain the basic metabolic rate (BMR) – heart beat, circulation of blood, maintenance of body temperature, breathing, etc., and to sustain additional activities of the person b) enables to growth processes and assimilation to take place by providing the necessary basic materials c) sustains the health, by providing protection against diseases and raw materials for the production of secretions such as hormones and enzymes.
The amount of energy to be provided by a balanced diet for any person will depend on several factors: age, sex, body size, lifestyle, occupation, and the climate of the area he is in.
The proportion of the various food classes in a diet is also not the same for different persons, due to varying physical and physiological requirements.
The energy value of food and the energy requirements in human can be calculated in terms of heat energy. In the past, heat energy has been measured in calories which are defined as:
1 calorie is the heat required to raise the temperature of 1 g of water by 1° C.
With the introduction of the S.I units, the unit of heat used now is the joule, which is defined in terms of the work done. Mechanical work can be converted into an equivalent amount of heat, and therefore both can be measured in the same units. The relationships between these two units are as follows:
1 calorie (cal) = 4.2 joules (J)
1 kilocalorie (kcal) = 4200 joules
= 4.2 kilojoules (kJ)
The energy value of food is defined as the total amount of heat released when one gram of food is oxidized completely. It is measured in the units’ joules per gram (Jg-1). The following diagram shows the apparatus that can be used to measure to heat produced by the burning of food.
Vitamins are complex organic compounds. They are required in very small quantities to maintain our health. They play an important role as co-enzymes in various enzymatic reactions and for building and maintaining body tissues in healthy conditions. Various organisms do not need similar enzymes, e.g. humans need vitamin C but other animals do not. Plants are able to synthesis the vitamins required. Animals are unable to do so and have to obtain them from plants.
Vitamins are divided into two groups: a) fat-soluble vitamins (A, D, E, and K), and b) water-soluble vitamins (B and C). Fat-soluble vitamins are absorbed in the ileum with fat from the diet and stored in the body, especially in the liver. Water-soluble vitamins dissolve in body fluids. Excess water-soluble vitamins cannot be stored and are removed from the body in the urine.
The skins can synthesis vitamin D using sunlight. Other vitamins have to be taken in regularly, even though in very small quantities. Failure to do so can cause a lack of vitamins and cause deficiency diseases. A summary of the main vitamins essential in our diet, their sources, functions and deficiency symptoms is shown in the following table.
Our body needs about 20 minerals in very small quantities, just like vitamins, to maintain the health and a variety of functions in our body. The minerals can be grouped into (a) macro-minerals, and (b) micro-minerals. Macro-minerals are those needed in a bigger quantity (> 100mg / day) by our body. They include calcium, magnesium, potassium, phosphorus, sodium and chlorine.
Micro-minerals are those needed in really small quantities (< 100 mg / day) by our body. The more important ones include iodine, iron, copper, fluorine, manganese, selenium, cobalt, molybdenum, chromium, and zinc. A summary of the main vitamins essential in our diet, their sources, functions and deficiency symptoms is shown below:
Roughage is that part of the diet which cannot be digested. It consists largely of cellulose in plant cell walls. The human alimentary canal has no enzyme cellulose to digest the cellulose fibers. It add bulk to the food and enables the muscles of the alimentary canal to grip it and keep it moving by peristalsis, particularly in the large intestine. It helps to retain water, absorb poisonous substances from the gut and soften faces. Absence of roughage can lead to constipation and increase the risk of colon cancer. Examples of high fiber foods are cereals, fruits, vegetables, beans, and peas.
Water makes up a high proportion of all the tissues in the body and is essential constituent of normal protoplasm. Although it is not a nutrient, it plays an important role in many processes in the body.