NUTRITION

• Human, science that deals with nutrients and other food substances, and with how the body assimilates them. The extremely complex processes that nutrients undergo in the body—how they affect one another, how they are broken down and released as energy, and how they are transported and used to rebuild countless specialized tissues and sustain the overall health of the individual—are understood only approximately. Nevertheless, important nutrition decisions need to be made for the health of individuals, of groups such as the very young and the aged, and of entire populations suffering from malnutrition.

Essential Nutrients

• Nutrients are classified into five major groups: proteins, carbohydrates, fats, vitamins, and minerals. These groups comprise between 45 and 50 substances that scientists have established, mostly through experiments with animals, as essential for maintaining normal growth and health. Besides water and oxygen, they include about eight amino acids from proteins, four fat-soluble and ten water-soluble vitamins, about ten minerals, and three electrolytes. Although carbohydrates are needed for the body’s energy, they are not considered absolutely essential, because protein can be converted for this purpose.

ENERGY

• The body uses energy to carry on vital activities and to maintain itself at a constant temperature. By using a calorimeter, scientists have been able to establish the energy amounts of the body’s fuels—carbohydrates, fats, and protein. About 4 calories each are yielded by 1 g (0.035 oz) of pure carbohydrate and 1 gram of pure protein; 1 gram of pure fat yields about 9 calories. (A kilogram calorie, used in nutrition, is defined as the heat energy needed to raise the temperature of 1 kilogram of water from 14.5° to 15.5° C (58.1° to 59.9° F).) Carbohydrates are the most abundant foods in the world, and fats are the most concentrated and easily stored fuel. If the body exhausts its available carbohydrates and fats, it can use proteins directly from the diet or break down its own protein tissue to make fuel. Alcohol is also a source of energy and yields 7 calories per gram. Alcohol cannot be oxidized by the body cells but must be processed by the liver into fat, which is then stored by the liver or in the adipose tissue.

FOOD TYPES

• The food can broadly be divided into following groups: -

  (1)   Energy yielding food Carbohydrate and fats.

  (2)   Body building food-Protein and minerals.

  (3)   Protective Food- Vitamin and minerals

Carbohydrates 

• More than 50 per cent of energy content of the common diet comes from carbohydrates. For a normal person about 70 g. of proteins and about 400 to 500 g. of carbohydrates are recommended. The requirements of a growing child, a nursing mother and during certain disease generally increase. A sportsman needs two and a half times more carbohydrates than a resting person.
• There are three groups of carbohydrates:

  Monosaccharides (C6H12O6): They are the simplest forms of carbohydrates, which cannot be further hydrolysed into basic units of carbohydrates, e.g. Glucose, Fructose, Calactose.

  (ii)   Disaccharides (C12H22O11): They give two molecules of Monosaccharides on hydrolysis eg. Sucrose, maltose and lactose.

         Sucrose                 Glucose+Frustose

         Maltose                 Glucose+Glucose

         Lactose                 Glucose+Galactose

  (iii)  Polysaccharides: They are made up of a large number of monosaccharides linked together in a straight or branching chain. Its general formula is C10(H2O)n. eg. starch, cellulose and glycogen where n is equavalent to 300 or more for starch and at least 300 or more for starch and at least 3000 for cellulose.

• Potatoes, bread, rice, sweet corn etc. contain high percentage of starch, which is a useful energy yielding substance. Sweet foods contain sugars. In animals and plants several other forms of carbohydrates like glucose, maltose and lactose are found. Glycogen is an insoluble carbohydrate found in the liver and muscles of animals. In the event of deficiency of energy, glycogen is rapidly converted into glucose, which is carried to the different parts of body by the blood. Cellulose is present in all plants since it is the main constituent of cell wall. Very few animals can digest it. Herbivores have special part in their gut where microorganisms act on cellulose and break it down but in most animals it remains unchanged and contributes to the roughage in the diet.
• Digestion and Absorption of Carbohydrates: In carbohydrate digestion the complex carbohydrate molecules are broken down into monosaccharides by the addition of water. This process is known as hydrolysis.
• The first step, in the digestion of starch is its conversion to maltose with the help of amylase; a large amount (40%) is digested in the mouth by salivary amylase. When the ‘chyme’ enters  the stomach, part of the undigested starch is hydrolysed by the HCl present in the gastric juice. The total digestion is accomplished in the intestine, where it is exposed both to pancreatic and intestinal amylase.
• The other carbohydrates that are the disaccharide sucrose, lactose, and maltose are digested in the intestine by the enzymes Invertase. b-glucosidose, and a-galactosidase respectively. Evidently glucose is the most abundant end product (80%) of carbohydrate digestion. The other are 10% galactose, and 10% fructose. The enzymes responsible for starch digestion are intracellular enzymes released when mucosal cells break apart.
• The digested carbohydrates are absorbed through the intestinal villi. There are two mechanisms of absorption in the intestine i.e. diffusion and active absorption. Fructose is transported by simple diffusion in response to a concentration gradient by the absorptive cells of the villi. Glucose and galactose are actively transported. Of the three monosaccharides, glucose is immediately transported throughout the body fluids. Fructose and galactose however are converted into glucose in the liver and then transported to different parts of the body, thus the end product of carbohydrate digestion is glucose. The concentration of glucose in blood is about 90-mg/100 ml. (optimum level).
• After the ingestion of heavy metal the glucose level in portal veins may raise two folds. Some of the excess glucose is taken up by tissues for oxidation, but most of its taken up by muscle and liver for storage as glycogen, this process is facilitated by the hormone Insulin. When blood glucose level falls, the glycogen is reconverted to glucose under the influence of hormone glucagons and transferred to blood, this is called glycogenolysis. Hence liver is an efficient buffer organ for blood glucose level as when glucose level rises, it is stored and when the glucose level falls it is again compensated.
• When the blood glucose level falls very low and is not adequately compensated by the liver glycogen, then glucose is synthesized from proteins and to some extent from fats. This is known as gluconeogenesis, and is a very important phenomenon as it provides glucose to the blood even during starvation, because the amount of glycogen present in liver is not sufficient to maintain the blood glucose for more than 24 hours. When glucose is not available cells are able to utilise fats for energy. The ganglion cells of the brain are unable to utilize fats, and without glucose they die quickly.

Fats and Oils

• It constitutes a major source of energy, about twice that of carbohydrates. It is advisable that the normal diet of 3000 K. Cal should contain at least 75 g of fats. This should always be raised when there is a significant increase in the energy expenditure of the body.
• Like carbohydrates, fats contain only carbon, hydrogen, and oxygen but in different proportion. They are compounds of glycerol with fatty acids.
• Fats remain solid at 20C but oils are liquid at high temperature. Butter, cooking oils etc. consist almost entirely of fat but milk, cheese, egg, some fishes, nuts and even meat contain considerable amount of fats. Fat can be stored in the body providing useful energy reserves. The layers of fatty tissues lying just below the skin have insulating function. During starvation, after fat reserves have been depleted, the body can use protein for energy.
• Digestion and Absorption of Fats: The digestion of fat is airs a hydrolytic process in which the lipids are broken into fatty acids, glycerol and glycerides. Fats are digested by the enzyme lipase secreted in the stomach, pancreas, and intestine. There is no bulk digestion of fat. Small part of the fat is digested in the stomach with the help of gastric lipase. But most of the fat digestion takes place in the small intestine. When the fat enters the small intestine they are acted upon by the brittle salts simultaneously released from liver. As the bile salts have a detergent action, they emulsify the fat into small globulins known as micelles which offer a greater surface area for lipases to act, and are further degraded by intestinal and pancreatic lipases into the product of fat digestion - fatty acid, glycerol and mono and diglycerides. In the fat digestion only 50% fat is completely digested to fatty acid and glycerol, the remaining 50% glycerides.

Protein

• It is the most significant constituent of the diet. The basic unit of protein in amino acids. Certain amino acids, though vital for the maintenance of the body are not synthesized by the body itself. These are called essential or indispensable amino acids. Conversely, non-essential and dispensable amino acids are those, which are synthesized, in the human body. Man requires in his diet eight of the twenty amino acids from which he can synthesize the other twelve. Animal foods such as milk meat or egg contain almost all the essential amino acids. They are referred to as low quality protein. Hence, when vegetable sources are to be relied upon for proteins. It becomes necessary that a combination of cereals and pulses be consumed in the proportion of 10:1 to meet the body requirement of the essential amino acids. The different amino acids are required:

  (1)   To form new tissues during the period of growth or pregnancy.

  (2)   To overcome wear and tear.

  (3)   To maintain the protoplasmic structure of the cell.

  (4)   To provide milk proteins during lactation.

  (5)   To furnish the raw materials for the manufacture of external secretions such as digestive enzymes and some protein hormones.

• The protein requirements per day of various age groups are: -

  Children between 2-8 years 22-3 g

  2.    Children between 13-17 years 43-53 g.

  3.    Moderately active males and females 45-56 g.

  4.    During pregnancy 65 g.

  5.    During lactation 70 g.

• Digestion and absorption of proteins: During digestion the proteins, first gets hydrolysed, the end products of protein digestion, are amino acids. Digestion of proteins in initiated in the stomach by the action of the enzyme pepsin. Pepsin is secreted by the chief cells of stomach is an inactive form, pepsinogen. Pepsinogen is converted into pepsin in the presence of H+ which is provided by HCl. HCl is secreted by the parietal cells. Pepsin attacks the peptide linkages adjacent to the aromatic amino acids and breaks the protein into proteoses, peptones, and polypeptides. The proteoses are the largest fragment. Peptones are smaller and polypeptides are smallest containing very few amino acids.
• The milk of the diet is clotted by another gastric enzyme known as rennin; the coagulated caesin (a milk protein) is then acted upon the pepsin. Rennin is found in large quantities in infants.
• When the semi digested proteins (proteoses, peptones, and polypeptides) reach the small intestine they are acted upon by trypsin and Chymotrypsin, which are simultaneously poured from pancreas. The two enzymes (Trypsin and Chymotrypsin) break the proteoses, peptones and polypeptides into small fragments. The polypeptides thus formed are finally hydrolysed by peptidases, which break the terminal bonds and release the individual amino acids. Peptidases are secreted by intestine and pancreas.
• At the end of protein digestion although most of the protein are converted to amino acids, a part is left in the form of small polypeptides.
• The free amino acids are absorbed both by diffusion at transport. From the absorptive cells of the intestine. The amino acids enter the blood from where these go to the liver. In certain cases, some of the unchanged proteins may act as antigens for producing antibodies. When sufficient quantities of antibodies are formed further absorption of protein produces a reaction in the form of ashes or asthmatic conditions. An individual is then said to be allergic to a particular protein.
• A common stock or metabolic pool of free amino acids is maintained in blood, liver, and tissues from the amino acids absorbed in the gastrointestinal tract and those obtained for the breakdown of body protein. Part of these is utilized for building body tissues, hormones, and enzymes etc. and the remaining are degraded to form nitrogenous wastes.
• The body protein is extremely labile and is continuously renewed eg. Half of the protein of liver and muscle is renewed every 10th and 160th days, respectively. The synthesis of protein from amino acids is under the control of anabolic hormones such as testosterone and GH. Breakdown of proteins to amino acids is controlled by catabolic hormones such as ACTH. The protein metabolism in the body therefore, is in a state of constant flux. Nearly all cells of the body have a free amino acid pool from which they are capable of synthesizing proteins. When the amino acid level of one part of the body falls. Amino acids from other parts are mobilized and transferred to the deficient organ.

Minerals

• A wide variety of salts is essential for the metabolic activities of the body and for the construction of certain tissues, they are needed to build bones, teeth, in blood coagulation, functioning of muscles, nerves, thyroid gland, and formation of RBC and providing resistance against diseases. Except Sodium Chloride (Common Salt) minerals are not taken in as pure salts, they enter as charged ions eg K, Mg2 or in organic compounds like the phosphorus in nucleic acids. Iron is an essential parts of hemoglobin’s calcium, magnesium and phosphorus are important for bones and teeth, Sodium and Potassium are essentially found in all cells, in the blood and in nerve cells. Iodine is essential for proper functioning of thyroid gland Minute traces of copper cobalt and manganese are essential to the body for different functions. Several others like lead, mercury Arsenic and Cadmium are poisonous are even very small amounts. Adequate requirements of some important minerals in the diet per day are as follows:

Mineral salts and their importance

Vitamins

•  Although these have no energy value, they are important accessory substances, which contribute to the maintenance of health ‘Funk’ for the first time, used the terms vitamin. Plants can make vitamins from simple substances, but animals mostly obtained them readymade directly on indirectly from plants. Minimum requirements of vitamins in the diet per day, sources of different vitamins and deficiency symptoms are given below: 

WATER

• Water is a universal solvent in the body. It is medium in which all metabolic reactions take place. It is obtained in dietary liquid, solid food, and also by oxidation of organic foodstuffs. Water, besides becoming a part of protoplasm, tissue fluid, is important for transporting substances from one part to another part and eliminating wastes outside the body. It also plays an important role in regulating body temperature and osmotic pressure of the body fluid.

NUTRITIONAL DISORDERS
Protein Caloric Malnutrition (PCM)

a.     Kwashiorkor: When small babies, instead of taking their mother’s milk, take mainly a carbohydrate diet the children become irritable, cease to grow and lose weight, the skin becomes dark. The body swells due to retention of water by the cells (oedema). Brain development and mental capacities are retarded, the liver too is damaged and the child often dies before the age of five. Millions of babies in Asia. Africa and Latin America suffer from this deficiency disease. In the absence of milk a protein rich diet obtained from animals or from soyabean or a combination of wheat, gram peanuts and jaggery can effectively cure this disease.

b.     Marasmus: Infants below the age of one year show a significant drop in body weight when breast feeding is replaced by less nutritive food, low in proteins and calories as a result of muscle degeneration, there is thinning of limbs and of the abdominal wall. The ribs look more prominent intestinal digestion is impaired, body growth and brain weight are lowered. Skin pigmentation and oedema are however absent. The disease can be cured by taking adequate amounts of proteins and carbohydrates.

Mineral Deficiency Disease

• Chlorine, Sodium, Calcium, Phosphorus, Potassium, iodine, Iron, Zinc, Sulphur and Fluorine are some of the common minerals essential for the healthy physiological functioning of the body. Their deficiency leans to many diseases. Some of them are:

  a.     Anaemia: This results from insufficient iron in the diet; consequently, there is deficiency of hemoglobin in the Red Blood Corpuscles (RBC). Since haemoglobin plays a vital role in the transport of oxygen, enough oxygen is not made available to cells to meet the metabolic requirements i.e. for oxidation of nutrients and production of energy, the person suffering from anaemia look pale, loose appetite and get fatigued easily. Eating meat liver green leafy vegetables such as spinach and fruits (banana, guava) helps in recovering from this ailment.

  b.     Hypokalemia: Sometimes, severe loss of potassium occurs in the body due to excessive secretions of hormones of the adrenal cortex or in the course of severe vomiting and acute diarrhea. This causes rise in heart beat rate, kidney, damage, weakness and paralysis of muscles.

  c.     Hyponatremia: An increased loss of sodium from the body, after intense vomiting and diarrhea, leads to dehydration, low blood pressure and even loss of body weight.

  d.     Goitre: It is caused by deficiency of iodine. Consequently, the thyroid fails to secrete enough thyroxine. The absence or very low level of thyroxine steps up the production of Thyroid Stimulating Hormones (TSH) by the anterior pituitary, the increasing level of TSH brings about the enlargement of thyroid known as goitre. People living in areas with low iodine content in water are therefore advised to use iodized common salts containing 0.01% potassium iodide.

Vitamin Deficiency Diseases

a)     Vitamin A: This is fat soluble and is commonly found in animal fat, milk, butter, and yellow fruits, such as papaya and mango, carrot and leafy vegetables. Its deficiency causes retarded growth, xerophthalmia (Dry eye, which is conducive to subsequent bacterial infection and eventual blindness), dermatosis or dry and scaly skin, night blindness, resulting from failure of the normal regeneration of visual purple after its lights induced charge i.e. on exposure to dazzling light one is not able to see in the dark or even in dim light.

(b)   Vitamin B Complex: The disease Beriberi is caused by the deficiency of thiamine, patients complain of extreme weakness, swelling and pain in the legs, loss of appetite, headache, shortness of breath, and even paralysis. By the deficiency of riboflavin (Vit. B2), resulting in blurred vision, burning and soreness of eyes and tongue, dermatosis and cracking of skin at angles of mouth the disease is called Ariboflavinosis. Inadequacy of niacin cause pellagra, in which the tip and lateral margins of the tongue, mouth and gums become red and swollen and later develop ulcers, the skin on hands, feet, elbows, wrists, and knees also become red and itchy and is peeled off causing pigmentation in patches. Deficiency of cyanoco-balamine (B12) affects the formation of RBC in the bone marrow; this leads to the reduction in the haemoglobin content of the blood, resulting in megaloblastic anaemia, Vit. B Complex is a group of water-soluble vitamins present in nuts, liver milk, yeast, unpolished rice and unmilled pulses.

c.     Vitamin C: Lemons, oranges, grape fruits, tomatoes, guavas, mangoes, amlas, and uncooked green vegetables are rich sources of vitamin c or ascorbic acid. It’s deficiency leads to scurvy. Patients of scurvy exhibit symptoms of general weakness, pain in the joints, decline in weight and anaemia, the gums become spongy, swollen, and bleed easily, teeth become spongy, swollen, and bleed easily, teeth become loose and fragile, large dosages of ascorbic acids helps in combating common cold and certain vital infections.

d.     Vitamin D: Its deficiency causes rickets in children and osteomalacia in adults. Rickets occur due to loss of bone calcium, and results in softness and deformities of bones such as bow legs and pigeon chest. Enamel of teeth also becomes thin and shows pits. In osteomalacia, there is softness and pain in bones, which fracture easily. Adequate exposure to sunlight and supplementing food with liver, eggs, and cod liver oil help to avoid these ailments.

e.     Vitamin E: It is essential for the normal development of sperms. Deficiency of this vitamin causes sterility in rats, rabbits, and guinea pigs. Since the germinal epithelium degenerates. Immobile sperms are produced. The vitamin also acts as part of an enzyme system in preventing excessive cell oxidation, thereby preserving vitamin A and unsaturated fats.

f.     Vitamin K: The first observation that absence of this vitamin causes hemorrhage was made in 1929 while experimenting on chicks. The intestinal symbiotic bacteria of mammals produce this vitamin in sufficiency quantities. Vitamin K occurs in two forms-K1 and K2, the former occurring in many plants and the latter in fishmeal. The vitamin has a role in photosynthesis. It helps in coagulation of blood in higher animals by the release of Piothrombin into the blood.

VIRUSES

• (Latin-Venom or poisonous fluid): The viruses were first discovered by lwanowski (1892) as extremely small microorganisms. The viruses are the simplest forms of life which instead of having cellular organization (viz. plasma membrane, cytoplasm and nucleus) similar to bacteria, blue green algae, plants and animals contain definite genetically determined macromolecular organization, genetic material and characteristic mode of inheritance.
• It is very difficult to categories, viruses in any one of two groups of living and non-living. Because the viruses are non-living outside the cell body (host) and can even by stored in bottles for any length of time just like non-living things. They lack a necessary energy yielding and synthetic enzyme system and therefore they can not lead an independent mode of life Viruses replicate and behave like living beings only within the living cells. For this reason they are a link between living and non-living things, and al are strictly parasitic.
• Differences between bacteria and viruses

  1.    Viruses have only one type of nucleic acid either DNA or RNA. Whereas bacteria have got both.

  2.    Viruses are devoid of ribosomes and the enzyme systems needed to generate ATP molecules. Whereas bacteria have got ribosomes as well as enzymes needed in ATP synthesis.

  3.    Viruses lack various cytoplasmic organelles. Whereas bacteria have cytoplasmic organelles.

  4.    Viruses do not have cell wall but bacteria have well defined cell wall.

  5.    Viruses cannot multiply or synthesize their proteins and enzymes independent on the host cell, but, bacteria can.