Nutrition, nourishment, or aliment, is the supply of materials – food – required by organisms and cells to stay alive. In science and human medicine, nutrition is the science or practice of consuming and utilizing foods.

Nutrients are the substances that form foods. These may include the following:  Carbohydrates

They provide us with energy and can be mainly obtained from products of vegetal origin such as grain, beetroots and sugar canes.


Nutrients that facilitate growth and human tissue repair. They can be found in animal origin foods such as milk and dairy products, meat, eggs and fish, as well as in vegetal origin foods, for example seeds.

Fats or lipids

they provide us with an energy which can be stored in the body unless it is consumed. They can be found in vegetal origin foods – such as oil – and in animal origin foods too – such as butter and bacon.

Vitamins and minerals

They make vital functions (relation, nutrition and reproduction) work correctly. They tend to be mainly in fresh fruits and vegetables.


approximately three quarters of human body are water. We drink and expel about two litres every day.




Types of nutrition

Plant nutrition

Plant nutrition is the study of the chemical elements that are necessary for plant growth.There are several principles that apply to plant nutrition. Some elements are directly involved in plant metabolism. However, this principle does not account for the so-called beneficial elements, whose presence, while not required, has clear positive effects on plant growth.

A nutrient that is able to limit plant growth according to Liebig’s law of the minimum is considered an essential plant nutrient if the plant cannot complete its full life cycle without it. There are 16 essential plant soil nutrients, besides the three major elemental nutrients carbon and oxygen that are obtained by photosynthetic plants from carbon dioxide in air, and hydrogen, which is obtained from water.

Plants uptake essential elements from the soil through their roots and from the air (consisting of mainly nitrogen and oxygen) through their leaves. Green plants obtain their carbohydrate supply from the carbon dioxide in the air by the process of photosynthesis. Carbon and oxygen are absorbed from the air, while other nutrients are absorbed from the soil. Nutrient uptake in the soil is achieved by cation exchange, wherein root hairs pump hydrogen ions (H+) into the soil through proton pumps. These hydrogen ions displace cations attached to negatively charged soil particles so that the cations are available for uptake by the root. In the leaves, stomata open to take in carbon dioxide and expel oxygen. The carbon dioxide molecules are used as the carbon source in photosynthesis.

Animal nutrition

Animal nutrition entails the study of the composition and characteristics of the material consumed by the animal, the manner in which this material is metabolised (converted, utilised, and excreted) in the digestive tract and body cells of monogastric animals (pigs, broilers, layers), ruminants (sheep, cattle, goats), and lower digestive tract fermenters (horses, ostriches). The nutrient requirements of different species animals for various production functions are also addressed. Finally, this information is integrated in an economically feasible and practical system of animal nutrition to ensure that the optimal genetic production potential of animals is achieved.

Macronutrients (excluding fiber and water) provide structural material (amino acids from which proteins are built, and lipids from which cell membranes and some signaling molecules are built) and energy. Some of the structural material can be used to generate energy internally, though the net energy depends on such factors as absorption and digestive effort, which vary substantially from instance to instance. Vitamins, minerals, fiber, and water do not provide energy, but are required for other reasons. A third class dietary material, fiber (i.e., non-digestible material such as cellulose), seems also to be required, for both mechanical and biochemical reasons, though the exact reasons remain unclear.

Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates range from simple monosaccharides (glucose, fructose, galactose) to complex polysaccharides (starch). Fats are triglycerides, made of assorted fatty acid monomers bound to glycerol backbone. Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen. The fundamental components of protein are nitrogen-containing amino acids. Essential amino acids cannot be made by the animal. Some of the amino acids are convertible (with the expenditure of energy) to glucose and can be used for energy production just as ordinary glucose. By breaking down existing protein, some glucose can be produced internally; the remaining amino acids are discarded, primarily as urea in urine. This occurs normally only during prolonged starvation.

Other dietary substances found in plant foods (phytochemicals, polyphenols) are not identified as essential nutrients but appear to impact health in both positive and negative ways. Most foods contain a mix of some or all of the nutrient classes, together with other substances. Some nutrients can be stored internally (e.g., the fat soluble vitamins), while others are required more or less continuously. Poor health can be caused by a lack of required nutrients or, in extreme cases, too much of a required nutrient. For example, both salt provides sodium and chloride, both essential nutrients, but will cause illness or even death in too large amounts.

Autotrophic Nutrition

Autotrophic nutrition means that simple inorganic substances are taken in and used to synthesise organic molecules. Energy is needed to achieve this. In photo-autotrophic nutrition light is the energy source. In most instances the light source is solar energy, the process being photosynthesis. Carbon dioxide and water are taken in by organisms and used to synthesise glucose, which can be broken down later during respiration to release the energy needed for life. By far the greatest energy supply to support food chains and webs is obtained from photo-autotrophic nutrition. Most producers use this nutritional method.

Chemo-autotrophic nutrition can also supply energy needs to some organisms. Simple inorganic substances are taken in and synthesised into organic molecules.  Chemical energy is the source for this process.

Each photosystem contains a large number of chlorophyll molecules. As light energy is received at the chlorophyll, electrons from the chlorophyll are boosted to a higher level and energy is passed to pigment molecules known as the reaction centre.

Here are two examples of chemo-autotrophs:

  • Nitrosomonas bacteria ammonia + oxygen = nitrite + water + energy
  • Nitrobacter bacteria nitrite + oxygen = nitrate + energy

The energy released in each of the above reactions is the result of the oxidation of inorganic substances. During respiration it is organic chemicals which are oxidised.

Heterotrophic Nutrition

Every non-autotrophic organism which depends on others for their food is called heterotrophs. Heterotrophs include every animal and non-photosynthetic plant which are unable to prepare organic molecules on their own. Heterotrophic nutrition can be classified into three types, based on the ways in which organisms obtain their food:

Saprophytic Nutrition

Saprophytes (animals which follow saprophytic nutrition) feed on dead and decayed organisms for energy. They consume dead and decayed remains of animals and plants. In this way, they help clean the environment. Some examples of saprophytes are fungi and certain types of bacteria. These are also responsible for the staling of bread, cakes etc.Saprophytes release certain enzymes to act on the complex organic matter and break it into simpler substances which can be easily consumed by them.

Parasitic Nutrition

Organisms which feed on other organisms by deriving out nutrients from other animals (hosts) are called parasites. Parasites extract the nutrients from the host and are harmful to their health, sometimes they even kill the host. Both animals and plants may serve as host.

In the case of a parasite, the host is never in benefit. Few examples of parasites are louse on a human head, Cuscuta plant, and tapeworms.

Holozoic Nutrition

Human follows the holozoic mode of nutrition. Holozoic nutrition means the feeding of solid and liquid food by animals. This involves the steps of ingestion, digestion, absorption, assimilation, and excretion. Ingestion is the intake of food, which is broken down into simpler organic matters by a process called digestion. After extraction of useful components, every other unwanted and indigested particle is excreted out. Other holozoic organisms are animals like cat, deer, dog etc. and also amoeba.

Holozoic nutrition

Holozoic nutrition is a type of heterotrophic nutrition that is characterized by the internalization (ingestion) and internal processing of gaseous, liquis or solid food particles. Protozoa, such as amoebas, and most of the free living animals,such as animals, exhibit this type of nutrition.  In Holozoic nutrition the energy and organic building blocks are obtained by ingesting and then digesting other organisms or pieces of other organisms, including blood and decaying organic matter. This contrasts with holophytic nutrition, in which energy and organic building blocks are obtained through photosynthesis or chemosynthesis, and with saprozoic nutrition, in which digestive enzymes are released externally and the resulting monomers (small organic molecules) are absorbed directly from the environment.

parasitic nutrition

In this type of nutrition, the organisms (called parasites) depend on the body of other living organisms (called their host) for getting their food. Many viruses, bacteria, fungi and animals have this mode of nutrition.  The organisms which depend on other living organisms (host) for food are called as parasites.

Parasites of two types:

Ecto parasites

Ecto parasites are those parasites which obtain their food from their host by remaining outside the body of their host. For example, mosquitoes, ticks, lice and bed bug.

Endo parasites 

Endo parasites are those parasites which obtain their food from their host by remaining inside the body of their host. For example, Ascaris, plasmodium vivax and tape worm.

Symbiotic nutrition

Symbiosis is a close ecological relationship or association between the individuals of two (or more than two) different species.   In symbiosis, at least one member of the pair benefits from the relationship. The other member may be injured (parasitism, relatively unaffected (commensalism), may also benefit (mutualism). In other words, at least one member of the partner gets symbiotic nutrition.

Bacterial endosymbiosis has a recurring importance in the evolution of insects. Approximately 10-20% species of insects depend on bacterial associates for their nutrition and reproductive viability. In nutritional symbiosis, both mutuals contribute to each other organic nutrients, inorganic minerals, or digestive enzymes. Some important examples of nutritional mutualism are: nitrogen fixation, Mycorrhiza (fungus and root association), Syntrophy (mutual production of biochemical substances and nutrients), and Lichen.

Several types of symbiotic nutrition are known, the well studied example of symbiotic nutrition is nitrogen-fixing associations (between various species of bacteria and leguminous plants). Some of the more important associations are listed below. In symbiotic associations the plants is identified as the host and the microbial partner is known as the microsymbiont. The most common form of symbiotic association result in the formation of enlarged, multicellular structures, called nodules, on the root (or occasionally the stem) of the host plant. In the case of legumes, the microsymbiont is bacterium of one of three genera’s: Rhizobium, Bradyrhizobium, or Azorhizobium. Collectively, these organisms are referred to as Rhizobia. Curiously, only one nonleguminous genus, Parasponia (of the family Ulmaceae) is known to form root nodules with a Rhizobia symbiont.

A limited number of non-nodule-forming associations have been studied, such as that between Azolla and the cyanobacteria Anabaena. Azolla is a small aquatic fern that harbors Anabaena in pockets within its leaves. In Southeast Asia, Azolla has proven useful as green manure in the rice paddy fields where it is either applied as manure or co-cultivated along with the rice plants. Because more than 75% of the rice acreage consists of flooded fields, free living cyanobacteria and anaerobic bacteria may also make a significant contribution. These practices have allowed Asian rice farmers to maintain high productivity for centuries without resorting to added chemical fertilizers.

Lichen is a common example of nutritional symbiosis. They are symbiotic organisms made up by the association of green algae or cyanobacteria and filamentous fungi. They co-exist in an obligate and intimate, but ectosymbiotic, association. The body of lichen is mainly made of a close network of fungal mycelium and is responsible for absorption of nutrients, water, minerals, and gases. Phycobiont, which comprise about 10 percent of the thallus, are set in in the compact mass of mycelium and are responsible for nitrogen fixation, production of food, and photosynthesis for both partners.


An insectivore is a carnivorous plant or animal that eats insects. An alternative term is entomophage, which also refers to the human practice of eating insects.  The first insectivorous vertebrates were amphibians. When they evolved 400 million years ago, the first amphibians were piscivores, with numerous sharp conical teeth, much like a modern crocodile. The same tooth arrangement is however also suited for eating animals with exoskeletons, thus the ability to eat insects is an extension of piscivory. At one time, insectivorous mammals were scientifically classified in an order called Insectivora. This order is now abandoned, as not all insectivorous mammals are closely related. Most of the Insectivora taxa have been reclassified; those that have not yet been reclassified remain in the order Eulipotyphla.

Some important terms of nutrition process

Amino acids

Amino acids are the building blocks of all proteins. There are 20 different amino acids that combine in different sequences to make all the proteins required for metabolism and growth. Our body can manufacture 12 of these amino acids from recycled proteins; however the other eight need to be derived from the food we eat.


Anaemia is the term used for a number of medical conditions when there is too little red blood cells, or they are too immature or do not contain sufficient haemoglobin to carry adequate oxygen to the tissues. The most common causes are nutrient deficiencies, excessive bleeding or red cell destruction.


Anthocyanins are natural pigments that occur in plants, fruits and vegetables. They give plants the blue and red colours as seen in blueberries and plums. They belong to a group of plant compounds called flavonoids, and are believed to behave as antioxidants.


Antioxidants assist in protecting your body against the damage caused by free radicals by neutralising them. Free radicals are very reactive compounds formed in the body due to both external factors such as smoking, exposure to the sun, air pollution and internal factors such as the body’s normal metabolic processes and the immune system. Free radicals can attack healthy cells in the body leading to cataract development and other conditions of ageing.

Basal metabolic rate (BMR)

BMR is a measurement of the level of energy required to maintain the bodys vital life functions. Measured when the body is at complete rest.

Bioavailability Bioavailability is the ease at which a substance can be absorbed from the digestive tract and into the bloodstream. The higher the bioavailability, the greater the absorption.

Body mass index (BMI)

BMI is a measure of a persons body size by calculating their weight in relation to their height. BMI = kg/m2.

Bone density

Bone density is a measure of the strength of a bone by determining the amount of minerals (e.g. calcium) in relation to the amount of bone. Bone density increases throughout childhood and adolescence to peak at about 30 years of age then slowly declines as we continue aging.




Bran is the outer layer of a grain. It is a good source of fibre, vitamins and minerals. The bran is present in wholegrain cereals and breads but is lost during the refining process that is used to make many products such as white bread.


Carotenoids are the orange, yellow and red pigments found in plant tissue that allow it to carry out photosynthesis. When eaten, these pigments provide vitamins and antioxidants that have many health benefits in humans. Beta-carotenes are a form of vitamin A.


Catabolism is the breaking down of a larger molecule into a smaller molecule. For example the breakdown of carbohydrates to release energy.

Central obesity

Central obesity refers to the excess fat stored around the abdominal area including around the vital organs such as heart and liver.


Cholesterol is a sterol which is made by the body and is found naturally in animal products such as meat, eggs, poultry and dairy foods.

Compementary proteins

Complementary proteins are the proteins supplied by different foods that combine together to supply all the essential amino acids. The proteins present in one food complement the proteins in another food to supply any essential amino acids that the other may be missing.



Complete proteins

Complete proteins are foods that contain all the essential amino acids in levels required by the body and do not require other foods to supply any.


Dehydration occurs when body water loss exceeds intake. This generally occurs due to insufficient water consumption or increased water loss due to vomiting, diarrhoea or excessive sweating. Symptoms include thirst, headaches, dry lips, lack of concentration. Mild dehydration can occur before you notice any symptoms.


Diabetes mellitus is a disease caused by the inability of the body to control the amount of sugar (glucose) in the blood. Type 1 diabetes results from the bodys inability to produce insulin in the pancreas and Type 2 diabetes is due to the body cells developing resistance to insulin.


Electrolytes are minerals which are needed to keep the body’s balance of fluids at a healthy level and to maintain normal functions, such as heart rhythm, muscle contraction, and nerve impulse transmission. Electrolytes include potassium, sodium, calcium, and magnesium.


Emulsifiers are substances that have both water-soluble and fat-soluble portions. This feature allows oils and water to combine in a solution.


Energy is the fuel we need from food to function and be active. Energy requirements vary depending on your age, body size and physical activity. It’s important to monitor your energy consumption as too much energy can lead to weight gain. Fat, protein and carbohydrates all provide energy (known as kilojoules or calories) in the foods we eat. Fats provide more energy per gram than protein or carbohydrates.


Enzymes are substances that speed up chemical reactions. For example, in our body some enzymes help break down the food we eat and release energy.

Fat (saturated)

Saturated fat is fat that consists of triglycerides containing only saturated fatty acid radicals. There are several kinds of naturally occurring saturated fatty acids, which differ by the number of carbon atoms, ranging from 3 carbons (propionic acid) to 36 (Hexatriacontanoic acid). Saturated fatty acids have no double bonds between the carbon atoms of the fatty acid chain and are thus fully saturated with hydrogen atoms.


Fibre plays a key role in preventing constipation, cancer and heart disease. Wholegrain breads, cereals, legumes, rice, pasta, fruit and vegetables are good sources of fibre. There are a number of different types of dietary fibre. The three major types are soluble fibre, insoluble fibre and resistant starch. (Although it is not actually a fibre, resistant starch is now being recognised as a member of the ‘fibre family’ due to its similar effects on the body.)

Food intolerance

A food intolerance is an adverse reaction (that does not cause an immune response) of the body to compounds found in a variety of foods. Common symptoms are irritation of the stomach or bowels, hives, mouth ulcers, nausea, nasal congestion and diarrhoea.


To fortify is to add nutrients to a food in levels higher than were originally present. Fortification can be mandatory to prevent a widespread nutritional deficiency, for example folate in bread, or voluntary to balance the total nutrient profile of a food.

Free radicals

Free radicals refer to atoms that have unpaired electrons in their outer layers. Caused by pollutants, cigarette smoke, and the by-product of metabolism they are believed to contribute to tissue damage and aging.


Gluten is a protein found in wheat, rye, barley, triticale and possibly oats (dependant on cross-contamination during processing). It is the gluten that gives dough its sticky cohesiveness which is important in manufacturing many products such as bread.


Goitre is an enlargement of the thyroid gland due to iodine deficiency or malfunction of the thyroid gland.


Haemoglobin is a protein found in red blood cells that carries oxygen from the lungs to the cells throughout the body.


Insulin is a hormone produced in the pancreas in response to increased blood glucose levels. Insulins primary role is to transport glucose from the bloodstream into the muscle and tissues.


Lycopene is a phytochemical found in fruit and vegetables which gives them a red pigment. Lycopene can be more easily absorbed by the body if it has been gently cooked.




Metabolism refers to the chemical processes that occur in our body that turn what we eat into energy. This energy can then be used for all activity including walking, talking, thinking and breathing.


Micronutrients is the general name given to compounds that are needed in minute quantities to sustain a healthy body, such as vitamins and minerals.


Phytoestrogens are a type of plant chemical that have a similar structure to the hormone oestrogen, however they are not identical in their effects. Two major types of phytoestrogens are isoflavones and lignans. Phytoestrogens occur naturally in legumes, wholegrain cereals, nuts and seeds, and many vegetables and fruits.


Vegan is the word that describes an individual who avoids all animal-derived foods from their diet, including honey and gelatine.


The word ‘wholegrain’ refers to a grain food where all parts of the grain (the germ, endosperm and bran layer) are intact and retained. Examples include wholegrain wheat and wholegrain (brown) rice. If the grain has been cracked, crushed or flaked, then in order to be called ‘wholegrain’, it must retain nearly the same relative proportions of bran, germ and endosperm as the original grain.

Digestion in unicellulor animal (amoeba)

Amoeba possesses a holozoic mode of nutrition and process is known as  “phagocytosis”. The basic processes involved in the nutrition  include:



Amoeba takes in its food through this process. Initially, it pushes out its pseudopodia so that it can encircle the food. After this, it engulfs the food, thus forming a bag-like structure called food vacuole. The process is known as “phagocytosis”.


This step follows ingestion. The food vacuoles are rich in various digestive enzymes. These enzymes break down large insoluble foodstuffs consequently yielding simple soluble molecules.


It is the process of absorption of the digested food material into the cytoplasm leaving behind the undigested food material. Sometimes the amoeba absorbs large quantities of food. What happens to the excess food? Well, the excess food gets stored in the form of glycogen as well as lipids.


This is the “utilization” process. During this process, the absorbed food is utilized for energy production, growth, repair as well as for multiplication.


Finally, the cell membrane gets ruptured so that the undigested food material is thrown out of the body.

Digestion in multicellulor animal grass hopper

Grasshopper (or cockroach) is a multicellular organism. So, in grasshopper (or cockroach) the different processes of nutrition takes place in fully developed digestive system. The digestive system is a system of organs and glands concerned with obtaining, digesting and absorbing nutrients from food. The digestive system of grasshopper (or cockroach) is divided into three parts:



The foregut of grasshopper (or cockroach) consists of following organs: mouth, oesophagus or food pipe, crop and gizzard.


The midgut of grasshopper (or cockroach) consists of stomach and ileum.


Colon and rectum constitutes the hind gut of a grasshopper (or cockroach).The whole process of digestion in grass hopper is as follows:

Ingestion:In grasshopper (or cockroach) food is ingested through the mouth with the help of forelegs and mouth parts.

Digestion: In grasshopper (or cockroach) the digestion of food starts in the mouth, where the saliva secreted by salivary glands mixes with the ingested food. The saliva contains some enzymes which digest starch present in the food. Saliva also helps in lubrication and softening of food. This partially digested food passes through the oesophagus into crop where it is stored temporarily. Then, the food passes into gizzard. Here, the food is finely ground by tough walls of gizzard. From gizzard, the food goes into stomach. In the stomach, the enzymes secreted by elongated glands called hepatic caeca get mixed with the food to digest it completely.

Absorption: The digested food is then absorbed by the walls of ileum when the digested good passes from the stomach into ileum.

Assimilation: The food absorbed by the walls of ileum is then supplied to all the parts of grasshopper (or cockroach) and is used to obtain energy, as well as for growth and repair of the body.

Egestion: The food not digested by grasshopper (or cockroach) goes from ileum to colon. Here water is absorbed from it. Finally, the undigested food is temporarily stored in the rectum. From the rectum the undigested food is removed out of the body through anus.

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