In this article, we will discuss about the principles of nutrition and balance diet.
Principles of Nutrition:
Food may be defined as any solid or liquid substance which when taken by the body provides it with necessary materials to enable it to grow, replace the worn-out and damaged parts and provide energy to function normally. The daily food intake has a direct influence on the health and well-being of an individual. Food is composed of different chemical elements.
Nutrients are molecules which the body uses to function appropriately and stay in a healthy condition.
It is the study of nutrients and their relationship with food and living beings.
The food that a person normally takes everyday.
Malnutrition means an incorrect or imbalanced intake of nutrients.
Means insufficient total intake of nutrients.
Basic dietary components:
There are five classes of basic components or nutrients:
(5) Minerals and trace elements.
The components under 1 to 3 are known as macronutrients, those under 4 and 5 are known as micronutrients.
Carbohydrates are not at all required in the diet. Yet, we consume large amounts of carbohydrates every day because they are the cheapest source of energy and easily available dietary sources. Carbohydrates are the main sources of energy to the body which provide about 70% of the daily calorie requirements. Carbohydrates, in addition to the supply of energy also serve as the components of cell membrane and receptors. Carbohydrates are very well synthesized in our body from non-carbohydrate sources.
Cellulose and stretch reflex:
Cellulose (polysaccharide) materials present in the diet form the bulk (fiber) of the food and cannot be digested by human beings because of the absence of the enzyme cellulase. The cellulose helps in the movement of the food through the G.I tract. The cellulose material of the diet absorbs the waste from large intestine and while doing so it stretches the wall of the large intestine and as a result, defecation takes place. This is called stretch reflex.
There is a metabolic disorder called diabetes mellitus wherein there is an increased level of glucose in the blood (hyperglycemia). Hyperglycemia affects the normal functioning of the kidney and brain leading to hypertension and other abnormalities. Hence, in diabetes mellitus patients, the blood glucose level should be kept under control, for which the carbohydrates should be restricted in the diet.
The energy requirements can be met with proteins and to a little extent by fats. But as human beings first and the foremost food i.e. milk tastes sweet due to the presence of a carbohydrate lactose, he has a craving for sweet and hence he should be supplied with some non-carbohydrate sweeteners.
Some of the non-carbohydrate sweeteners are saccharin, sodium cyclamate, monallin and aspartame. These sweeteners are also used in the milk powder supplied to children with lactose intolerance, wherein the milk is free from lactose but contains one of these sweeteners.
It is 400 times sweeter than table sugar. Saccharin is commercially used in large scales though it is banned scientifically at present. It is used as sweetener in diabetes and obesity. But it is harmful to human beings. When saccharin is given in large quantities in drinks and food it causes cancer. However as the risk is too low it is still used as an artificial non-calorie sweetener in the diet drinks specially of those who are diabetes.
It is 30 times sweeter than table sugar. It is a carcinogenic agent and has been banned from prepared foods.
It is 180 times sweeter than table sugar. It is a methyl ester of a dipeptide of two amino acids that normally occur in protein (i.e., aspartate and phenylalanine). As it is non-toxic, it is used as a sugar substitute in many foods. The sugar free tablets available in the market are all made up of aspartame.
It is a protein with a molecular weight of 11,000. It is 2100 times sweeter than table sugar. Its sweetness is due to the three dimensional conformation of the polypeptide. But this cannot be used in prepared foods because it looses its sweetness on heating or denaturation.
Fats are also not needed in our diet. But we consume it because of its high calorific values (1 g gives 9 Kcal) and also it can be easily stored with less amount of water and therefore occupy less space. These fats are also taken because of their essential fatty acid content. Essential fatty acids are those which cannot be synthesized in our body, hence they should be supplied through the diet.
They are ‘linoleic acid’ and ‘linolenic acids’. Arachidonic acid is also an essential fatty acid but it can be synthesized from linolenic acid. They are also a good source of fat soluble vitamins viz., A, D, E & K. Plant fats are superior to animal fats because they contain more of polyunsaturated fatty acids i.e. essential fatty acids and less of cholesterol. The cholesterol in the diet should be restricted because excess intake of cholesterol leads to its deposition in the tissues thereby causing atherosclerosis.
Proteins are needed for their content of certain amino acids that are essential to human body for the biosynthesis of proteins, body repair in adult and for body building and body repair in children. Human body proteins are made up of only 20 standard amino acids out of which nearly 10 amino acids can be synthesized in the body but the remaining 10 cannot be synthesized in the body hence they have to be supplied through the diet. Therefore they are known as essential amino acids.
The essential amino acids are:
M — Methionine (semi essential)
V — Valine
P — Phenylalanine
A — Arginine (semi essential)
I — Isoleucine
H — Histidine
T — Tryptophan
L — Leucine
Ly — Lysine
T — Threonine
The nutritional value of a protein depends on two factors:
(1) Its content of the essential amino acids
(2) Its digestibility.
The amino acid content of all the proteins is not the same. One will be deficient in one amino acid and the other in another type of amino acid. Some proteins are not completely digested to liberate all the amino acid contents, ex. the protein rich portions of wheat grains are not completely digestible.
It is a condition in which the intake of protein nitrogen (AA) exactly balances the loss of nitrogen in the urine and faeces. If the intake is more than the output due to nitrogen retention as tissue protein then the subject is said to be in positive nitrogen balance. If the intake is less than the output (as in old age and illness) then the subject is said to be in negative nitrogen balance.
Biological value of protein:
The biological value of a protein is a factor that is inversely proportional to the amount of a given protein source that must be consumed to keep an adult human in nitrogen balance. If the protein taken in the diet has all the essential amino acids in good proportions, is completely digested and is completely absorbed then that protein is said to be a good protein or it is said to have 100% biological value.
A protein of cent percent biological value should also completely replace the nitrogen lost in the urine. Generally animal proteins have higher biological value than plant proteins, because the animal proteins are much alike the human proteins and hence they have more digestibility and absorbability, for example egg and milk portions have their biological values near 100% (94% & 96% respectively).
Most of the plant proteins have low biological values and are said to be poor proteins. If two vegetable proteins are taken in combination, called succotash, then this mixture of proteins will have good biological value (though not 100%). Ex. the corn proteins are low in lysine but contain adequate amounts of tryptophan whereas bean proteins contain adequate amounts of lysine but are low in tryptophan.
Neither is a good protein. But a mixture of the two is a good source of having balanced amino acids. If beans are taken in the breakfast and corn in the lunch (i.e. after 5-6 hours) then it will be of no biological value because amino acids cannot be stored. Therefore the biological value of vegetable proteins can be improved if taken along with animal proteins for the daily protein supply. It is recommended that 1/3rd to 1/2 of the proteins may be derived from animal proteins like egg, meat and milk.
Protein sparing action of carbohydrates and fats:
Carbohydrates and fats spare the proteins and make then available for anabolic or constructive purpose. Carbohydrates and fats supply the required energy and so proteins will not take part in energy metabolism, especially in patients needing tissue repair, this action is seen.
A balanced diet can be defined as the nutrients required for sustaining and keeping the human body in metabolic health. It can also be defined as nourishment (food) required for maintaining normal life. Balanced diet is one which contains all the food constitutes in proper proportion to meet the energy and nutritional requirements of the individual. The components of a well-balanced diet will vary depending on age, sex, physiological needs such as pregnancy and lactation and nature of physical activity.
While designing the quality and quantity of a balanced diet the total calories are distributed among 3 classes of food in the following proportion:
i. Carbohydrates- 50-70%
ii. Fats- 20-30%
iii. Proteins 10-15%
Proximate principles of diet:
The proximate principles of diet are:
i. Carbohydrates: the energy yielding substances.
ii. Fats: yield energy and act as insulating materials.
iii. Proteins: act as building materials and bear the wear and tear of the body.
Construction of a diet-the spectrum of food:
The food is divided into four basic food groups:
1. Milk group:
Two glasses of milk or servings of cheese, cottage cheese, ice creams, or other dairy products.
2. Meat group:
Two servings of meat, fish, poultry or eggs, peas, beans or nuts.
3. Vegetable and fruit groups:
Four servings of green or yellow vegetables, tomatoes, citrus fruits.
4. Bread and cereal group:
Four servings of whole grains or fortified cereal products. There is no single perfect food that provides all nutritional needs for everyone. The 40 different required nutrients occur in very different proportions in different foods. Therefore a variety, within each group is essential.
Functions of food:
1. Milk, egg and meat:
They provide the essential amino acids and have high nutritional values ranging from 98-100%. Butter supplies the fat soluble vitamins A, D and E.
Cereals supply vitamin B, and roughage (fibrous or cellulose material).
3. Essential fatty acids:
Prevents atherogenic disorders. Vegetables contain phytosterol which helps in reducing serum total cholesterol.
Citrus fruits like orange prevent diseases like scurvy, constipation etc. Fruits supply potassium required by the body to prevent diabetic coma.
Green leafy vegetables will help in the synthesis of Hb and provide some vitamins like vitamin A, folic acid, etc. Vegetables including green leafy vegetables prevent constipation by acting as roughage (cellulose materials).
Recommended dietary allowances (RDA):
The food and nutritional board of National Academy of Sciences, National Research Council has developed a table of recommended daily dietary allowances (RDA) of various nutrients for optimum nutrition of infants, children, adults, pregnant & lactating women and various conditions of health and diseases to provide an ample safety margin of life.
Formulation of a diet:
A correct diet must provide for maintenance of the body as well as energy requirements, for growth and reproduction. The essential elements lost by the body by excretion must be replaced.
The important factors are:
1. Energy value:
The average caloric requirement of an adult male and female should be met by the food provided daily.
2. Quality and quantity of the constituents of food:
(a) Primary foods (proteins, fats and carbohydrates):
Proteins, fats and carbohydrates are consumed in the ratio of 1: 1: 4. 3000 calories are provided by 100 grams of protein, 100 grams of fat and 400 grams of carbohydrates. It is advisable that 10-15% of the total calories should be obtained from protein, 20-30% from fat and 50-70% from carbohydrate.
(b) Secondary foods (vitamins and minerals):
These are essential in the diet but in very minute quantities to enable utilization of primary foods.
Although water is not a food, it is ordinarily consumed in the diet and serves a prime role in the health of the body. Hence it is one of the components of food.
3. Variation in the diet:
There is a risk of missing some essential elements or vitamins in a varied diet. Eskimos live mainly on fish and meat and poor Orientals chiefly live on rice with small amounts of fish and meat.
4. Digestibility of the food:
The food is of no use if it is not digested in the alimentary canal. Digestibility is more concerned with absorbability. When fats and starch are largely used, vegetables and animal proteins are not absorbed. Absorption is enhanced with a mixed diet than when the substance is taken alone.
Food consistency is considerably changed on cooking. Harmful organisms are destroyed. Cooking breaks down the connective tissue fibres of meat and makes meat easier to masticate and helps in digestion. Overcooking shrinks the coagulated protein and decreases the digestibility.
Cooking increases the water content and digestibility of vegetables. Cellulose frame work is loosened and starch from starch grains is liberated. Fats are not changed much upon cooking. Cooking enhances the flavour of the food. However, vitamins B and C are destroyed when vegetables are cooked.
6. Psychological factors:
Appetite is reduced by worry and anxiety. Digestion is also upset due to imperfect mastication and secretion of digestive juices. Consumption of food is increased while taken in pleasant surroundings and good company with different items.
Dietary food is much influenced by family income. When the income is good, consumption is high with all the protective foods. A poor income has poor protective foods. Lowest income group having low protective foods suffer form rickets and nutritional anemia. They are less resistant to infectious diseases.
Based upon the above it can be concluded that a balanced diet should contain proteins (70 gms), fats (50 gms), carbohydrates (440 gms), calcium (0.8 gms), phosphorus (1.4 gms), Iron (40 mg), vitamin A (1300 I.U.), Vitamin B1 (1.8 mg) and vitamin C (200 mg). In addition to this 2-3 liters of water and other elements must be included in the daily diet.