CLASSIFICATION OF FOOD

CLASSIFICATION OF FOOD

By

Dr. Mrs. O.K. Israel6/04/2020

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Introduction

• Food is a basic need of human race because, it contains the nutrients essential to life (i.e. health and well-being of the body)

• The food eaten is broken down in the body into a number of important constituents which, when ingested, digested, assimilated, and absorbed are circulated by the blood to the various organs that need the nutrients

• Food can be defined as anything either solid or liquid possessing a chemical swallowed, to do more of three things, which include:• Provide the body with materials which can produce heat, or other forms of

energy• Provide materials for growth, maintenance, repair or reproduction• Supply substances which normally regulate the production of energy or the

processes of growth, repair or reproduction 2

Classification of foods

• There are many ways of classifying foods:1. Classification by origin:

• Foods of animal origin

• Foods of Vegetable origin

2. Classification by chemical composition:

• Carbohydrates

• Proteins

• Fats and oils

• Vitamins

• Minerals 3


4. Classification by predominant function• Body –building foods e.g. milk, meat, poultry, fish, eggs, pulses, groundnuts etc.• Energy-giving foods e.g. cereals, sugars, roots, tubers, fats & oils• Protective foods e.g. vegetables, fruits, milk

5. Classification by nutritive value• Cereals & millets• Pulses(Legumes)• Vegetables• Nuts & oilseeds• Fruits• Animal foods• Fats & oils• Sugar• Condiments & spices• Eggs• Milk & milk products 4

NUTRIENTS

• Organic and inorganic complexes contained in food are called nutrients. They are broadly divided in to:

•Macronutrients:• -proteins

• -fats

• -carbohydrates

•Micronutrients:• -vitamins

• -minerals5


• Classification by chemical composition

• Carbohydrate:• It provides a great part of the energy in all diets• It’s the most abundant organic constituents of plants • They serve as the major source of chemical energy for living

organisms (e.g. sugars and starch), as well as important constituents of supporting tissues (e.g. cellulose).

• It is essential for the oxidation of fats and for the synthesis of certain non-essential amino-acids

• The cheapest & easily digestible fuel of humans is carbohydrate• In the diet of poor people, especially in the tropics, up to 85% of

the energy may come from this source• In the diet of the rich people in many countries the proportion

may be as low as 40%6


• Classification of Carbohydrates• Classified into three major structure & complexity. They are:

• Monosaccharides• Disaccharides• Polysaccharides

• Monosaccharides• it is a simple carbohydrate that consists of only one saccharide or sugar

unit and they are non-hydrolysable• e.g. glucose, fructose & galactose

• Disaccharides:• Are carbohydrates that yield two monosaccharide molecules on

hydrolysis• e.g. sucrose, lactose & maltose 7


• Polysaccharides:• These are complex sugars that contain several monosaccharides joined

together

• They are broken into simple sugars in the body by hydrolysis

• There are three important polysaccharides - starch, glycogen, and cellulose

• Starch is the principal food reserve of plants

• Glycogen (animal starch) functions as a carbohydrate reserve for animals and man

• Cellulose is insoluble & it serves as structural material in plants

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• Sources of Carbohydrate

• Carbohydrates may be found in the following four food groups:• Cereals & cereal products

• Vegetables

• Fruits

• Concentrated sweets e.g. sugars, syrups, jellies, beverages, candies, honey

• Functions of Carbohydrate• Supplies energy which serves as body fuel for daily activities

• It spares protein from being used as a source of energy

• It supplies glucose to the body

• It helps the body to burn fat 9


• It adds flavor to the diet

• It helps in the formation of genetic materials

• It provides energy for the microorganism that synthesize some of the B-complex vitamins

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• Proteins:• Are essential class of food that are made of complex organic

molecules called amino-acids• They are the most important organic substances & as such they

take the first place, nutrition wise• They have long been recognized as fundamental structural

elements of every cell of the body• They contain carbon, hydrogen, nitrogen, Sulphur, phosphorus &

iron

• Sources of Proteins

• These can be classified into two:• Animal proteins• Plants proteins

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• Animal proteins:• They are food from animal sources & they supply proteins of high biological

value

• They are the first class of proteins because they supply all the essential amino-acids

• e.g. eggs, cheese, meat, poultry, fish, milk & milk products

• Plant proteins: are found in• legumes (beans, peas), nuts (cashew nuts), cereals (corn, wheat, guinea corn,

millet, rice), vegetables and fruits

• They are known to be the second class proteins

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Classification of foods• Functions of Protein

• Supply amino acids for building of new tissues, normal growth of infants, the maintenance of body tissues & replacement of damage or worn out tissues

• Help in the formation/synthesis of hormones, enzymes & antibodies that fight against infection

• Helps to maintain fluid balance within the body (maintain the acid base balance of the blood and tissues)

• It is important in regulatory functions acting as biocatalyst in every biological process in the body

• Its important in the formation of nucleic acid, DNA & RNA, the bearer of inheritance characteristics

• They are also useful in the formation of hemoglobin which carries oxygen in the blood

• They are also used as an alternative source of energy, when the calorie intake is inadequate, even though this is considered wasteful

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Classification of foods• Classification by chemical composition

• Fats and oils:• Fats are the class of food substance that are normally solid at

room temperature

• Oils are fats that remain melted or in liquid state at room temperature

• They are commonly found in plants and animals

• They are concentrated sources of energy. The amount of energy in fats and oils double that of carbohydrate & protein

• Fats yield fatty acids & glycerol on hydrolysis

• Fatty acids are divided into: • saturated fatty acids (e.g. lauric, palmitic & stearic acids) and

• Unsaturated fatty acids 14


• Unsaturated fatty acids are further divided into:• monounsaturated fatty acids (e.g. oleic acid) &

• Polyunsaturated fatty acids (e.g. linoleic acid)

• Saturated fatty acids are mainly found in animal fats

• Polyunsaturated fatty acids are mostly found in vegetable oils

• However, there are exceptions: • e.g. coconut & palm oils, although they are vegetable oils, have an

extremely high percentage of saturated fatty acids

• Fish oils, although they are not vegetable oils, contain poly & mono unsaturated fatty acids

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Classification of foods• Classification of Fats

• Visible & invisible fats

• Saturated & unsaturated fats

• Visible fats• are those fats that can be seen clearly, slightly hard & moist to touch

• It is easy to estimate their intake in the daily diet

• e.g. butter, margarine, vegetable oils etc

• Invisible fats • are hidden fats, not clearly noticed, not visible to the naked eye

• they are present in almost every article of food

• It is difficult to estimate their intake in daily diet

• the major contribution to total fat intake is from invisible sources rather than visible sources

• e.g. present in milk, meats, eggs, fishes, nuts, chocolates, ice-cream etc 16

Classification of foods• Saturated fats

• are fats that are solidified at room temperature & cannot be easily oxidized

• Unsaturated fats• are fats that are liquid at room temperature and can be easily oxidized

• Sources of Fats

• The dietary sources of fats may be classified as:• Animal fats – e.g. butter, milk, cheese, eggs, fat of meat & fish etc.

• Vegetable fats – e.g. groundnut, mustard, sesame, coconut etc.

• Functions of Fats & Oils• Serves as concentrated source of energy

• They provide insulation and protective cushion for organs of the body e.g. heart, liver, intestine etc

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• Functions of Fats & Oils contd• Maintenance of the function & integrity of cellular & sub-

cellular membranes in tissue metabolism• Helps the body to transport fat soluble vitamins (vitamin

A, D, E, K) • They make meal palatable, appetizing & satisfying • Important for growth & normal functioning of the body

cells• Fat beneath the skin provides insulation against cold• Dietary fat stored in adipose cells in human helps man

survive without food for weeks18


• Vitamins and Minerals

• Vitamins and minerals act as regulators and catalysts for a variety of bodily functions.

• Vitamins are essential for:• Building body tissues such as bones, skin, glands, nerves, and blood.• Assisting in the metabolism of proteins, fats, and carbohydrates • Promoting healing• Preventing nutritional deficiency diseases.

• Minerals are essential for:• The formation of strong bones and teeth• Helping to control the nervous system• Fluid balance in tissues• Muscle contractions

• Minerals and most vitamins must be supplied through diet since they are not synthesized in the body.

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• Vitamins:• Are a class/group of organic compounds categorized as essential

nutrients

• They are micronutrients

• They do not yield energy but enable the body to use other nutrients

• They are required by the body in very small quantity for the normal metabolism of other nutrients

• The body is unable to synthesize most vitamins and as such they must be obtained from some other source 20


• They function as catalyst

• They are easily obtainable from food although, the content varies from food to food and one food cannot supply all of them in sufficient amounts for health

• A well balanced diet supplies in most instances the vitamin needs of a healthy person

• Classification of vitamins - vitamins are classified as:• Fat soluble vitamins

• Water soluble vitamins

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• Fat soluble vitamins• These are vitamin A, D, E, & K

• As the name implies, they can only dissolve in fat

• Water soluble vitamins• Are vitamins that can only dissolve in water

• These are vitamins of B-group & vitamin C

• The B-group vitamins e.g. B1, B2, Niacin, B6, B12, etc

• Each vitamin has a specific function to perform & deficiency of any particular vitamins may lead to specific deficiency diseases

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• Fat soluble vitamins

• Vitamin A• This includes both pre-formed vitamin, retinol & a pro-vitamin, beta

carotene, some of which is converted to retinol in the intestinal mucosa

• Sources• Vitamin A is widely distributed in animal & plant foods• In animal foods as pre-formed vit A (retinol), & in plant foods as

pro-vitamins (carotenes)• Animal foods – foods rich in retinol are liver, eggs, butter, cheese,

whole milk, fish and meat. Fish liver oils are the richest natural sources of retinol 23

Classification of foods• Plant foods –• The cheapest source of vitamin A is green leafy vegetables such as

spinach & amaranth• The darker the green leaves, the higher its carotene content• Vit A also occurs in most green & yellow fruits & vegetables e.g.

mango, pumpkin, melon, pawpaw, carrots etc• Carotenes are converted to vitamin A (retinol) in the small

intestine• Functions of Vitamin A

• It is essential for normal vision (good eye sight), It contributes to the production of retinal pigments which are needed for vision in dim light

• It is necessary for maintaining the integrity & the normal functioning of glandular & epithelial tissue which lines intestinal, respiratory & urinary tracts as well as the skin & eyes

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• It supports growth especially skeletal growth

• It boost the immune system

• Deficiency of Vitamin A

• The signs of vit. A deficiency are predominantly ocular manifestation

• These include: Night blindness, conjunctival xerosis, bitot’s spots, corneal xerosis & keratomalacia

• It can cause follicular keratosis i.e. blocking of the sweat gland & tear gland

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• Vitamin D• The nutritionally important forms of vitamin D in man are Calceferol

(vitamin D2) & Cholecalciferol (vitamin D3)

• Sources• Vitamin D is unique because it is derived both from sunlight and

foods• Sunlight : Vitamin D is synthesized by the body by the action of UV

rays of sunlight on 7-dehydrocholesterol, which is stored in abundance in the skin

• Foods : Vit. D occurs only in foods of animal origin e.g. Liver, egg yolk, butter, cheese & some species of fish• Fish liver oils are the richest source of vitamin D

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• Functions of Vitamin D• Promotes intestinal absorption of calcium and phosphorus

• Stimulates normal mineralization of bone and teeth

• Deficiency of Vitamin D• Rickets – This is the deficiency of vitamin D in young children.

There is reduced calcification of growing bones

• Osteomalacia – This is the deficiency of vit. D in adults. It occurs mainly in women, especially during pregnancy & lactation when requirements of vitamin D are increased

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• Vitamin E• This is called tocopherol

• Sources• From vegetable oils, cotton seed oils, egg yolk, butter etc

• Functions of Vitamin E• It aids fertility• It delays ageing process

• Deficiency of Vitamin E• Can cause nerve of muscle damage• Poor vision• Reduce fertility 28


• Vitamin K

• Occurs in at least two major forms – vitamin K1 & vitamin K2

• Vitamin K is stored in the liver

• Sources• Vitamin K1 is found mainly in fresh green vegetables (particularly

dark green ones) & in some fruits

• Vitamin K2 is synthesized by intestinal bacteria

• Vitamin K requirement of man is met by a combination of dietary intake & microbial synthesis in the gut

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• Functions of Vitamin K

• The role of vitamin K is to stimulate the production and/or the release of certain coagulation factors

• Deficiency of Vitamin K• In vit. K deficiency, the prothrombin content of blood is markedly

decreased & the blood clotting time is considerably prolonged leading to bleeding disorders

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• Water soluble vitamins

• Vitamin B1• This is also known as Thiamine

• Sources• Important sources are: whole grain, cereals, wheat, yeast, pulses,

oilseeds & nuts, especially groundnut

• Meat, fish, eggs, vegetables & fruits contain smaller amounts

• Milk is an important source of thiamine for infants (provided the thiamine status of their mothers is satisfactory)

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• Functions of Vitamin B1 (Thiamine)• It helps in the metabolism of carbohydrates

• It promotes good appetite

• Deficiency of Vitamin B1 • Beriberi (disorder of the nerves which may lead to paralysis of legs

& heart failure)

• Wernick’s encephalopathy characterized by ophthalmoplegia, polyneuritis, ataxia & mental deterioration

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• Vitamin B2• Also known as Riboflavin

• Sources• The richest natural sources are milk, eggs, liver, kidney & green

leafy vegetables• Meat, fish, cereals & pulses contain small amount

• Functions of Vitamin B2 (Riboflavin)• It is a co-factor in a number of enzymes involved with energy

metabolism (i.e. it helps release energy from proteins, fats, & carbohydrates, thereby helps to maintain the body energy supply)

• It helps to maintain healthy skin, eyes, nerves & muscles

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• It helps to maintain healthy skin, eyes, nerves & muscles

• Deficiency of Vitamin B2• Riboflavin deficiency always occur in association with deficiencies

of other B-complex vitamins (such as pyridoxine)

• Riboflavin deficiency impairs the optimal utilization of pyridoxine (vit. B6)

• The most common lesion associated with riboflavin deficiency is angular stomatitis

• Other clinical signs include cheilosis, glossitis etc

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• Vitamin B3• Also known as Niacin or Nicotinic acid• It differs from the other vitamins of the B-complex group in that an

essential amino acid, tryptophan serves as its precursor

• Sources• Liver, Kidney, meat, poultry, fish, legumes, groundnut, peas

cereals, etc

• Functions of vitamin B3 • It is essential for the metabolism of carbohydrate, fat & protein• It is also essential for the normal functioning of the skin, intestinal

& nervous system35


• Deficiency of Vitamin B3• Niacin deficiency results in Pellagra

• Pellagra is characterized by three D’s – diarrhea, dermatitis and dementia

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• Vitamin B6• Also known as Pyridoxine

• Sources• Found in cereals, liver, soya beans, peanut, green leafy vegetable, meat

etc.

• Functions of Vitamin B6• It plays an important role in the metabolism of amino acids, fats, and

carbohydrate

• Deficiency of Vitamin B6• Pyridoxine deficiency is associated with peripheral neuritis

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• Vitamin B12• Also known as cyanocobalamin

• Liver is the main storage site of vitamin B12

• Sources• Liver, Kidney, meat, fish, eggs, milk, & cheese

• It is also synthesized by bacteria in the colon

• Functions of Vitamin B12• It is crucial to the normal function of the brain & the nervous

system

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• It is involved in the formation of red blood cells

• It is involved in the synthesis & regulation of DNA

• Deficiency of Vitamin B12• Megaloblastic anaemia (pernicious anaemia)

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• Folate• Alternative name is folacin

• The usual pharmaceutical preparation is folic acid

• Sources• Liver, meat, diary products, milk, fruits, cereals, green leafy

vegetable etc

• Functions of Folate• It plays a role in the synthesis of the nucleic acids (which

constitute the chromosomes)

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• It helps in the formation of haemoglobin

• It is needed for the normal development of blood cells in the marrow

• Deficiency of Folate• It results in Megaloblastic anaemia, glossitis, cheilosis, &

gastrointestinal disturbances

• Severe folate deficiency may cause infertility or even sterility

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• Vitamin C• The chemical name is Ascobic acid

• It is the most sensitive of all vitamins to heat

• Sources• It is best found in citrus fruits e.g. lemon, limes, grape, pineapple,

oranges etc

• Other sources include banana, carrots, guava & green leafy vegetables

• Functions of Vitamin C• It is necessary for the growth, development & repair of all body

tissues 42


• It is involved in the formation of collagen

• Helps in the absorption of iron

• Important in the healing of wounds

• Helps to boost the immune system

• Helps in the maintenance of cartilage, bones, & teeth etc

• Deficiency of Vitamin C• Results in scurvy – signs include: swollen & bleeding gums,

subcutaneous bruising or bleeding into the skin or joints, delayed wound healing, anaemia & weakness

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CLASSIFICATION OF FOOD