Biology – Classes of Food

Topic: Classes of Food


  1. Meaning of food
  2. Classes of food and their functions

Meaning of food

Food is any edible substance either liquid or solid which when eaten is used by the body to maintain life. It is any nutritious substance that people or animals eat or drink, or that plants absorb, in order to maintain life and growth. Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as fats, proteins, vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism’s cells to provide energy, maintain life, or stimulate growth.

Food is any substance consumed to provide nutritional support for the body.

Classes of food

Nutrients are chemicals found in foods that are essential to human growth and function.

There are six classes of nutrients: carbohydrates, fats, proteins, vitamins, minerals and water. All six have certain functions that target a different body part, and together, they ensure the state of our overall health. Some of the different functions of some nutrients are listed below in more detail:


Carbohydrate molecules are made up of carbon, oxygen, and hydrogen atoms. Monosaccharides like glucose, fructose, and galactose are types of carbohydrates. An example of a complex carbohydrate is starch.

Carbohydrates are classified based on the number of monomer units in them or the number of sugar units they have. They can be monosaccharides, disaccharides, or polysaccharides. Monosaccharides have one sugar unit, disaccharides have two sugar unites, and polysaccharides have three or more sugar units. Carbohydrates constitute majority of foods like bread, noodles, rice, and other products that have grains.

Monosaccharides and disaccharides are simpler carbohydrates while the polysaccharides are complex carbohydrates. Complex carbohydrates take longer to digest because they need more time to be broken down into simpler sugar units. Only the simpler sugar units can be absorbed by the blood. The spikes in the sugar levels of the blood are caused by too much consumption of simpler carbohydrates. The simple carbohydrates are absorbed by the blood very quickly which causes the blood sugar levels to spike abnormally.


  • It is the great source of energy which we need for basic functioning and physical activity
  • Carbohydrates are the primary source of fuel for our bodies, especially for our brain and during physical activity.
  • Sources of carbohydrates are rice, bread, yam, fufu, garri, etc


Protein is the major structural component of cells and is responsible for the building and repair of body tissues. Protein is broken down into amino acids, which are building blocks of protein. Nine of the 20 amino acids, known as essential amino acids, must be provided in the diet as they cannot be synthesized in the body. Proteins support the growth, repair and maintenance of tissues. The following are the foods that contain good sources of proteins; beans, meat, fish, nuts, etc. Other sources of protein are tofu, meat, eggs, soya and soya products, legumes, grains, and dairy products like cheese and milk.



Vitamins are an essential nutrient because they build and maintain healthy bones and muscle tissue. They also support our immune system, maintain the health of our blood, and ensure healthy vision. Vitamins are micro nutrients, meaning they are needed in small amounts to sustain our normal health and body functions. Some examples of common vitamins are Vitamin C and K, and the many B Vitamins.


  • Vitamins are an essential nutrient because they build and maintain healthy bones and muscle tissue.
  • They also support our immune system,It maintains the health of our blood, and ensure healthy vision.
  • Vitamins are micro-nutrients, meaning they are needed in small amounts to sustain our normal health and body functions.
  • Some examples of common vitamins are Vitamin C and K, and the many B Vitamins.


Minerals are chemical elements that are needed by living things. Carbon, hydrogen, nitrogen, and oxygen exist in organic molecules. The word mineral is archaic since it attempts to describe the less abundant elements needed by the human body. These elements are heavier than the basic four elements. These elements include metals which occur as ions more often in the body. Several dieticians advise that these minerals should be acquired from foods naturally. They are to be acquired in complex compounds or natural inorganic sources like calcium carbonate which can be derived from ground oyster shells. In another case, these minerals have to be added artificially in the form of supplements like iodine or iodized salt.

  • Minerals assist in the regulation of many body functions, some of which involve regulating fluids and producing energy and health of our bones and blood.
  • This nutrient also helps rid our body of harmful byproducts of metabolism. Some examples of well-known minerals are calcium, potassium, sodium and iron.


There are some elements that are essential and they have to be consumed in larger amounts. These minerals are referred to as bulk minerals. They can be structural and they could play several vital roles as electrolytes in the body. Here are some elements that have a recommended daily allowance or RDA with more than two hundred milligrams

  • calcium – this is a common electrolyte which also has structural purposes involving muscle health, digestive system health, bone health, the neutralization of acidity, the clearing of toxins, and helping in the streaming of blood throughout the body
  • chlorine – this is made up of chloride ions. It is a common electrolyte as well
  • magnesium – this is required for processing ATP or adenosine triphosphate, the energy of the body. It can also be used for related reactions like building bones, causing strong peristalsis, an increase in the alkalinity of the body, and an increase in the flexibility of the body
  • phosphorus – this is required for bones and it is essential in processing energy
  • sodium – this is a common electrolyte which is not usually found in dietary supplements. It is needed in large quantities. This is very common in food anyway. You can find it in the form of sodium chloride or common salt
  • sulphur – this is essential for amino acids and many proteins in the body like the skin, the hair, the liver, the nails, and the pancreas

Trace Minerals

Several elements are needed in trace amounts because they play a catalytic role with enzymes. Here are some of the trace mineral elements that are needed in less than two hundred milligrams everyday

  • cobalt – this is required for biosynthesis for the vitamin B12 family of coenzymes
  • copper – you need this for many redox enzymes which include cytochrome and oxidase
  • chromium – this is needed in order to metabolize sugar
  • iodine – this is needed for biosynthesis of the element thyroxin. This is needed in a much larger quantity compared to the others on this list. Iodine is usually classified as one of the macrominerals
  • iron – this is required for several enzymes especially haemoglobin and other proteins
  • manganese – this is needed for the processing of oxygen
  • molybdenum – this is required for xanthine and other oxidases
  • nickel – this is needed in urease
  • selenium – this is needed for peroxidase or the anti-oxidant proteins
  • vanadium – there is no current RDA for vanadium although it has been spotted in lower organisms. It has no specific biochemical function but it has been spotted in human beings
  • zinc – this is needed for enzymes like carboxypeptidase, the liver alcohol dehydrogenase, and carbonic anhydrase


Water helps to maintain homeostasis in the body and transports nutrients to cells. Water also assists in removing waste products from the body. All beverages and high-moisture foods such as soup and watermelon contain water and count towards your daily water requirement. Adults should consume 25 to 35 milliliters of fluids per kilogram body weight or 2 to 3 liters per day.


  • Water is one of the most important nutrients mainly because it is  important for our survival.
  • The appropriate intake of water maintains the balance of fluids inside and outside of our cells.
  • It is also critical because it assists in the regulation of nerve impulses, the excretion of waste products, muscle contractions and nutrient transport.
  • We consume water in solid forms such as fruits and vegetables as well as in liquid form such as juices and soups. Drinking eight to ten glasses of water will ensure that all the above body functions are carried out properly.

Fats and Oil

Fat is an energy source that when consumed, increases the absorption of fat-soluble vitamins including vitamins A, D, E and K. Twenty to 35 percent of your daily intake should come from fat. Choose healthy options such as omega-3-rich foods like fish, walnuts and vegetable-based oils. Omega-3s help with development and growth. Limit intake of saturated fats such as high-fat meats and full-fat dairy. Fats are either saturated or unsaturated. Saturated fats are those kinds of fats with all their carbon atoms bonded to hydrogen atoms with the fatty acid chains. On the other hand, unsaturated fats are characterized by carbon atoms that are double bonded with oftentimes few hydrogen atoms. Moreover, these unsaturated fats can be further classified into monounsaturated fats and polyunsaturated fats. Monounsaturated fats are made up of one double bond. Polyunsaturated fats are made up of several double bonds. Trans fats are a kind of unsaturated fat with a trans-isomer fatty acid and they are usually made through the process of hydrogenation.
Fats and Oil

  •  It plays a role in maintaining healthy cell membranes
  • Fats and oils support brain development and cognitive function in children.
  • Fats help to protect vital organs inside the body by providing a layer of cushioning.
  • They also insulate the body and regulate body temperature.
  • Fats slow gastric emptying and prolong satiety, which can help both children and adults feel more satisfied with their meal.

Test and Exercise

  1. Food can be defined as———–
  2. There are ———– classes of food (a) 6 (b) 3 (c) 12 (d) 8
  3. The great source of energy is (a) protein (b) vitamins (c) carbohydrate (d) water
  4. Examples of carbohydrate foods are all except (a) beans (b) rice (c) garri (d) vegetables
  5. Food is very important. True/False.    
    For more notes see:


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