Factors of a Correct Diet for Human Body | Nutrition

The following points highlight the seven main factors of a correct diet for human body. The factors are: 1. Energy Value 2. Quality and Quantity of the Constituents of Food 3. Variation in the Diet 4. Digestibility of the Food 5. Cooking 6. Psychological Factors 7. Cost.

Factor # 1. Energy Value:

The average caloric requirement of the adult male is 3,000 daily.

The figures of the daily caloric requirement of York in 1900 are given below:

Factor # 2. Quality and Quantity of the Constituents of Food:

(A) Primary foods (Protein, Fat and Carbohydrate):

a. Protein, fat and carbohydrate are con­sumed in the ratio of 1 : 1 : 4 in this coun­try.

b. 3,000 calories are provided by 1,00 grams of proteins, 100 grams of fat and 400 grams of carbohydrate.

c. Although the 1:1:4 ratio is prevalent in this country still wide variations of carbo­hydrate and fat may occur without harm.

d. It is advisable that 10%-15% of the total calories should be obtained from protein, 20%-35% from fat and 50%-66% from car­bohydrate.

Proteins:

Although the expected amount of protein is 100 gm per day, less amount can also maintain health and nitrogen equilibrium. Even 1 gm. per kg body weight may be ample. Larger amounts are neces­sary for growth, pregnancy and lactation.

Increased amounts may be required in wasting diseases. The protein requirements vary with the net protein uti­lization (NPU) of the dietary proteins. If the NPU is low, the requirements are high and if the NPU is high, the requirements are low.

The requirement of protein in the diet is not only quantitative, the qualitative aspect is also important since the metabolism of protein is con­nected with that of its constituent amino acids. Certain amino acids are called ‘essential’ because they must be obtained preformed and cannot be synthesized by the animal organism.

The remain­der, the so-called non-essential, is also required by the organism since they are found in the protein of the tissues, but they can be synthesized from α-keto acids by amination. Histidine in the diet is also necessary to maintain growth during child­hood. Such amino acids are said to be relatively essential. The nutritive value of a protein depends on its content of essential amino acids.

Some proteins, if they are the sole source of nitrogen, will not support life, whereas others are sufficient. Hence, proteins are of two types—first class or good protein and second class or poor pro­tein. First class protein can support life in the ab­sence of other forms of protein.

Proteins of animal origin (meat, milk and eggs) are almost completely utilized if taken alone whereas, 10% to 40% of veg­etable proteins (peas, beans, potatoes) may remain unabsorbed and excreted in the feces.

The absorp­tion of vegetable proteins is improved if taken with other foodstuffs. Animal proteins are associated with fat, but very little carbohydrate (except milk), whereas vegetable proteins are almost associated with a large amount of carbohydrate.

It has been observed that the dietary require­ment for protein is influenced markedly by the level in the diet of fat and carbohydrate.

These latter food­stuffs have a “Protein-sparing” effect. Fat, prima­rily, functions as a fuel (9 cal/gm.), carbohydrate also serves as a fuel (4 cal/gm.), but is required for the synthesis of certain catalytic compounds of metabolic cycles (e.g., oxaloacetate in the TCA cy­cle) and provides the carbon skeletons for the syn­thesis of the nonessential amino acids.

At least 5 gm of carbohydrate per 100 calories must be sup­plied if nitrogen equilibrium is to be maintained. Protein has a more catalytic function in the form of enzymes. In the absence of fat and carbohydrate from the diet, protein is degraded to provide fuel (4 cal/gm.) and catalytic compounds of metabolic cycles.

Essential amino acids may be broken down to supply the materials for the synthesis of nones­sential amino acids. For these increased burdens, the protein intake is ultimately increased. The pro­tein requirement is decreased when fats and carbo­hydrates are taken along with.

Proteins differ in biologic value depending on their content of essential amino acids. The proteins of eggs, dairy products, kidney and liver have high biologic value since they contain all of the essen­tial amino acids.

Good quality proteins include soya beans, peanuts, potatoes and the muscle tis­sue of meats, poultry and fish. Fair proteins are ce­reals and most root vegetables. Poor biologic value includes nuts and legumes. The mixture of poor and fair can provide good biologic value.

Proteins are also the important sources of ni­trogen, sulphur, and phosphorus for the body. Many amino acids have specific functions in metabolism such as methionine as a methyl donor, cystine as a source of – SH groups, the dicarboxylic acids (aspartic acid, glutamic acid) in transamination, tryp­tophan as precursor of niacin, arginine in the urea cycle, etc.

The protective substances in a diet are those which are essential for specific purposes other than energy production, i.e., first class proteins, mineral elements, and vitamins.

Fats:

Fat has high fuel value. It increases the palatability of foods. It has got high capacity to be stored as energy in the body. Fat provides the essential fatty acids such as linoleic, linolenic and arachidonic acids. Fats are essential for the absorption of fat- soluble vitamins.

Excess of saturated fat and cho­lesterol consumption is associated with hypercholesterolemia and atherosclerosis. A lack of fat causes a feeling of hunger shortly after a meal due to rapid digestion in its absence. Fat reduces the bulk of the food. The consumption of fat usually is over 80 gm. per day. It may increase up to 150 gm. with an in­crease of family income.

As a source of energy there is little difference between animal and vegetable fats. Animal fats have a better biologic value because they contain vita­mins A and D in particular. Animal fats are most used when the incidence of sunlight is low.

Fats provide fat-soluble vitamins and the es­sential fatty acid linoleic acid which is required for the synthesis of arachidonic acid from which prostaglandins are synthesized in the body. The major symptoms of essential fatty acid deficiency are a scaly dermatitis, hair loss, and poor wound healing.

Linoleic acid is widely distributed in the lipid portion of both plant and animal foods; veg­etable seed oils are especially rich sources.

In societies where fat is the principal food for energy intake, the population tends to develop coronary heart disease, obesity, and cancer of the bowel and breast. Blood cholesterol level can be reduced sig­nificantly by changing the diet containing less satu­rated fatty acids or cholesterol. The serum choles­terol level is the major factor for the development of atherosclerosis.

Carbohydrates:

Carbohydrate is the cheapest source of food. It can be readily digested, absorbed and utilized for pro­ducing energy. It is most efficient source of energy for vital processes. It can furnish 60%-80% of the total caloric intake in the scarcity of proteins and fats. It is bulky and liable to undergo fermentation producing acid (e.g., lactic acid) if digestion is de­layed. Hence, it is not wise entirely to replace fat by carbohydrate.

In gluconeogenesis, carbohydrate can be sup­plied from most amino acids as well as from the glycerol moiety of fats. A minimum of 5 gm. of car­bohydrate per 100 kcal of total diet is necessary to prevent the development of ketosis. Sufficient car­bohydrate should be included in the diet to have complete oxidation of fat. The amount is near about 400 gm. per day.

The chief carbohydrates are starch and sugars (from milk, fruits and vegetables as well as sucrose). Glycogen is only consumed in living tissues such as oysters. Carbohydrates are almost entirely de­rived from vegetable sources, Cellulose stimulates peristalsis. Some cereals, e.g., oatmeal contains much phytin as to interfere with the absorption of cal­cium.

Galactose is synthesized in the body and lac­tose is also synthesized from galactose in the body. Hence, no need of giving lactose to lactating women. Pentose’s are absorbed and excreted un­changed except ribose or deoxyribose. Sugar is valuable for muscular work in mini­mizing fatigue.

Sucrose (common table sugar) is one of the major etiologic factors in dental caries. This sugar is not the cause of diabetes, heart disease, or obes­ity.

Within this century, decrease in fibre consump­tion in industrialized countries has been accom­panied by a high incidence of diverticulosis, colon cancer, cardiovascular disease, and diabetes.

A large amount of dietary fibre decreases bowel transit time, alters the composition on intestinal bacteria, re­duces enterohepatic circulation of cholesterol, de­lays intestinal sugar absorption, and reduces the absorption of certain minerals.

(B) Minerals:

Some minerals are always required since small amounts of inorganic salts are always excreted. Fruits, vegetables and cereals are the chief sources of the mineral elements in the diet. Milk products supply the majority of the calcium and phosphorus in the diet.

Calcium:

a. Increased amounts of calcium are required by children, pregnant and lactating women.

b. Children, whose normal intake is low, can absorb a higher percentage of calcium in­gested than those with a high intake.

c. In many eastern countries, where little milk is taken, the average consumption by adults is about 400 mg daily but this low intake does not show any signs of calcium deficiency.

d. The average intake should be about 800 mg per day.

e. The best sources are cheese and milk. Other sources are eggs, green vegetables, oranges, nuts, buttermilk, beans, and car­rots. Meat, fish and fruits are poor sources of calcium.

Hard water is a source of calcium.

Phosphorus:

a. This is taken in organic and inorganic form.

b. Children should intake 1 gm. per day, adults 1.3 gm. and a pregnant or lactating woman 1.9 gm.

c. The best sources of phosphorus are ani­mal foods such as meat, fish, milk, cheese and eggs. Considerable proportions of the total phosphorus are provided by the vegetable foods such as beans, rye, oat­meal and lentils. Cereals provide phos­phorus in the form of phytic acid which interferes with the absorption of calcium. Hence, animal sources of phosphorus are better.

Iron:

a. It is an important constituent of the diet and its deficiency leads to anemia.

b. The more concentration of iron is from bread, meat and potatoes. Good sources are liver, kidney, egg yolk, green peas, cabbage, carrots and qereals.

c. Only less than 10% of iron is absorbed. In iron-deficient subjects about 20% may be absorbed.

d. Milk is very poor in iron. The infant is born with a store of iron which maintains for six months. After this period, iron is given along with food. Human milk con­tains 1 -2 mg iron per litre, cow milk less.

e. Children up to 12 years require 15 mg to 20 mg iron daily, adults require 40 mg daily, and the daily requirement of iron during pregnancy and lactation is 50 mg.

Iodine:

a. The daily requirement of iodine is 0.05 mg and iodine is obtained from water, vegetables and fish.

b. In certain localities, where the soil and wa­ter lack this element, simple goitre results due to dietary deficiency.

c. Fish, cod liver oil and vegetables can sup­plement iodine deficient diet.

Magnesium:

a. The average daily consumption of about 0.2 gm. is sufficient.

b. Good sources are meat, green vegetables and bread.

Copper:

a. The daily adult requirement is 2 mg.

b. Good sources are liver, oysters, cocoa, nuts etc.

c. Human and cow milks only contain about 0.6 mg per litre.

Sodium Chloride:

a. Ordinarily 20 gm of the salt is consumed per day.

b. The intake of the salt is only required if abnormal quantities are lost in sweat dur­ing severe muscular exercise at high tem­perature.

c. Heat stroke is prevented by ingestion of salt solutions instead of water.

Vitamins:

a. Normal persons get sufficient vita­mins in their diets and hence supplemen­tation with vitamin is not required. Only in diseased state in which digestion and absorption are impaired, the supplemen­tation with vitamin is most essential.

b. Many of the vitamins are destroyed by cooking and storage. Hence, fresh fruits and vegetables should be taken daily.

c. Cereals, when refined, lose B vitamins. Therefore, food is improved by the addi­tion of vitamins.

d. Deficiency symptoms of water-soluble vi­tamins consist of dermatitis, anemia, di­gestive difficulties, and neurologic disor­ders.

e. Most of the water-soluble vitamins act as coenzymes in metabolism of substrates.

f. Vitamin B₁₂ is synthesized by microorgan­isms. It is present only in meat and dairy foods. Therefore, strict vegetarians may be at risk for Vitamin B₁₂ deficiency.

g. The fat-soluble vitamins are mainly present in fatty meats, liver, dairy fats, egg- yolks, vegetable seed oil and leafy green vegetables.

h. Fat-soluble hypervitaminosis produces symptom of toxicity.

i. Deficiencies of fat-soluble vitamins occur primarily in young children who lack ad­equate body stores. Deficiencies are rare in adults unless there is malabsorption, biliary obstruction, or other conditions that affect fat metabolism.

Water:

Although water is not a food, it is ordinarily con­sumed in the diet. Hence, it is one of the compo­nents of food.

Factor # 3. Variation in the Diet:

a. There is a risk of missing some essential element or vitamin in a varied diet.

b. Eskimos live mainly on fish and meat but the poor Orientals chiefly live on rice with small amounts of fish.

Factor # 4. Digestibility of the Food:

a. The food is of no use if it is not digested in the alimentary canal.

b. Digestibility is more concerned with ab­sorbability.

c. When fats and starch are largely used, veg­etables and animal proteins are not ab­sorbed.

d. Absorption is more enhanced with a mixed diet than the substance taken alone.

Factor # 5. Cooking:

a. In cooking, food is considerably changed. Harmful organisms are destroyed.

b. Cooking breaks down the connective fi­bres of meat and makes meat easier to masticate and helps digestion. Overcook­ing shrinks the coagulated protein and decreases the digestibility.

c. Cooking increases the water content and digestibility of vegetables, cellulose framework is loosened and starch from starch grains is liberated.

d. Fats are little changed in cooking. Cook­ing enhances the flavour of the food.

e. When vegetables are cooked, Vitamins B, and C are destroyed.

Factor # 6. Psychological Factors:

a. Appetite is reduced by worry and anxiety and digestion is also upset due to imper­fect mastication and secretion of diges­tive juices.

b. Consumption of food is increased while taken in pleasant surroundings and good company with different items.

Factor # 7. Cost:

a. Dietary food is much influenced by fam­ily income.

b. When the income is good, consumption is high with all the protective foods. A poor income has poor protective foods.

c. The lowest income groups having the low protective foods suffer from rickets and nutritional anemia. The lower groups are less resistant to infectious diseases such as whooping cough, measles, diphtheria and tuberculosis.