FOODS AND THEIR CLASSIFICATION

Food Classification

This is means by which foods are grouped according to their similarities. The grouping of foods in most health institutions in many parts of Africa, especially Nigeria, is based on the function(s) of the most preponderant component of such foods. Thus, foods are classified as “energy foods”, “body-building foods”, “protective foods” or “accessory food substances” very much in line with the earliest food classifications. This classification is obviously obsolete, inappropriate or even misleading in the light of our improved knowledge and understanding of foods and nutrition, for practically all common foods offer at least two or more nutrients (see table 1.1 below), and thus, each foodstuff contributes substantially to the overall nutritional balance of the individual. The value of any food depends on its nutrient content that is directly responsible for the value or functions assigned to it. In a community where the consumer’s knowledge of nutrition and food and the resources for making a wise choice of the latter is rather limited, it is instructive to set out guidelines which can aid the consumer make these choices in order to meet the known nutritional needs. It is on the basis of these considerations that foods are classified.

The classification of foods is essential to the study of nutrition because by grouping together foods with similar nutrient content, it is possible to choose from a wide variety of alternatives if certain foods become scarce or money is in short supply. It includes choices that permit flexibility for seasonal, regional and budgetary considerations. Throughout the world, food groupings are used to translate nutritional needs into practical guidelines for food intake. These groupings are usually determined first and foremost, by their nutrient content. Thus, foods are grouped according to their similarity of nutrient content. A food that has a high nutrient density is one that has a high proportion of nutrients to the amount of calories supplied.

In most tropical countries, the poor economy, the socio-cultural factors and geographical locations and distribution of food have combined to limit the food choices of families. In these places, people subsist on whatever food is available to them. While certain foods may be totally unacceptable in a particular culture, it may well be a means by which many subsist in another. Thus, snails, insects, squirrels, rats, lizards, camels, horses and dogs are consumed. However, several imported modified foods are finding their way to the Nigerian/African table. Thus, semovita, macaroni and several other wheat and maize products are now available in local African markets.

Foods with high caloric densities have high proportions of calories for the amount of nutrient provided. In other words, such foods are high in fats, oils or sugar, but low in other nutrients, hence they are called “empty-calorie” foods. They are outside this classification.

This classification is a simple device used to outline the variety of foods that will provide a ‘balanced diet’ which include the essential nutrients. It goes without saying that no single food (not even milk) contains all the nutrients needed by the body in amounts sufficient to maintain life and promote a prolonged optimum growth. An individual must thus consume all the nutrients needed by the body from a variety of foods. Nevertheless, each food item supplies significant amounts of two or more nutrients. A cookie-eater who nibbles 10 chocolate chip cookies in a day, adds some 495 calories to his diet. He gets 5.7 g of proteins and almost 2 mg of iron (20% of male and 11% of female RDA for iron), a little vitamin A and some B-Complex vitamins. Therefore, most foodstuffs offer body building, energy and ‘protective’ properties depending on their quality (nutrient densities), quantity consumed and the physiological state of the individual consuming them. For example, while eggs, meat and milk might offer excellent proteins, with body building qualities, they, especially meat, also provide substantial amounts of energy, derived from their fat content as well as from the proteins. They may therefore provide greater amount of energy than the so-called energy (carbohydrate) foods. Furthermore, the proteins in the meat may not be used for tissue synthesis or for growth unless and until the energy requirements of the individual are first met. Moreover, fats which serve primarily as an energy reservoir or a concentrated form of utilizable energy is also required for the assimilation of several other nutrients, especially the fat-soluble vitamins, as well as for the synthesis of several essential compounds in the body. They serve as packing materials in the body to prevent heat loss and help to support the kidneys, eyes and other internal organs. They protect the ends of bones, giving shape to the body. Thus, fats are very important in terms of the structure and protection of the body from physical and physiological damages. Additionally, while milk may not supply a significant amount of iron, it could supply a significant amount of the daily requirement for proteins, calcium and niacin. Moreover, bread, rice and maize may each be contributing mainly carbohydrates, but each also contributes substantial proportions of the daily protein, vitamin and mineral requirement, especially when large quantities of each is consumed. Also, when each of these foods is combined with a legume (limiting only in lysine and the sulfur-containing amino acids), the resultant diet, together with the typical African sauce, constitutes a very important source of vitamins, minerals and proteins of a reasonably high quality. It has been estimated that the so-called starchy “energy foods“, such as cereals, provide more than 50% of the protein requirements of a normal adult human diet. Thus, it is the overall balance of the diet that is important; and this balance can accommodate a wide variety of foods. On the basis of these considerations, the following food groupings have been recommended for the tropical countries.

The Food Groups

On the basis of the above-mentioned rationale for grouping foods, the following five food groups are widely recognized around the world:

Milk Group:

It is from this group that the human infant gets its first taste of a human diet. The group is made up of all dairy products including fresh milk, skim milk, condensed milk, powdered milk, local and foreign cheeses, butter, yogurt and ice cream. Individuals with varying degrees of lactose intolerance have a choice of cheeses, butter milk, butter and yogurt. However, for those who must watch their weights, the use of ice cream and other milk-containing beverages should be restricted. However, this group is especially valued for its content of calcium, magnesium, riboflavin, cobalamin and proteins of high quality. But it is notably low in iron and ascorbic acid.

“Meat” Group:

This group includes such diverse food items as meats, poultry, eggs, fish, snails, shrimps, crabs and other sea foods; termites and other edible insects such as caterpillar, locusts, crickets and grass-hoppers; legumes (pulses), seeds and nuts. Although the nutritional contributions of each member of the group vary, they all provide valuable amounts of energy, proteins, iron and the B-complex vitamins. The proteins in the various cuts of meat do compare favorably well with the amounts of proteins available in poultry or fish. While the utilizable proteins in legumes consists of only about 30% of the amount of proteins available in the animal protein foods, other valuable components of the various foods in this group compare quite favorably well with meats, particularly in light of the high cost and the variable prices of the latter. Furthermore, since large amounts are consumed, legumes are perhaps the most important sources of proteins in many African diets, partly because they are relatively cheap, palatable and keep fairly well. Thus, eggs and legumes can be used quite freely to replace the high-priced cuts of meat without sacrificing adequate nutrition. Further-more, a greater use of legumes, nuts, poultry and fish would help to reduce the intake of saturated fat that is quite abundant in meats (beef is 20-30% saturated fat, compared with poultry and fish, which are 6% and 2-8% respectively).

Cereal Group

: The cereal grains belong to the family of grasses and they include maize, guinea corn (sorghum), wheat, rice, barley, oats and teff. But the latter three are not popular in Nigeria. However, all cereal grains have a fairly similar structure and nutritive value: 100 g of whole grain provides about 350 kcal, 8-12 g of proteins, and useful amount of calcium, iron (though phytic acid may hinder the absorption of these), and the B-Complex vitamins. The separation of cereals from tubers and starchy fruits is based on the differences in their ease of storage and protein, vitamin and mineral contents. Although they are of plant origin, the cereals contribute not only carbohydrates, but also the B-complex vitamins, iron, magnesium and generous amounts of proteins to the diet. As a group, they have an additional quality of ease of conversion into several important products that easily lend themselves to enrichment. It is believed that there is hardly any village in Africa where one cereal or another is not used as a staple food. As a group, cereals constitute the most important food for peoples all over the world, with approximately half of the people in the world depending heavily on rice, wheat and maize. The survival of the peoples of the Sahelian regions has been attributed to the consumption of cereals, limiting only in lysine and the sulfur-containing amino acids.

Starchy Fruit/Tuber Group: The members of this group include yams, coco-yams, cassava, potato, sweet potato, plantain and bread-fruit. These food crops are usually easily cultivated and are the staples in the wetter, more humid regions of Nigeria. They contain large quantities of starch and are therefore fairly easily obtainable sources of food energy. However, they are readily perishable and cannot be stored for long periods of time. Because of this, they are highly seasonal. As sources of energy, they supply about 385 kcal per 100 g of dry matter, but with very low amounts of other nutrients. They are inferior to cereals because they consist of about two-thirds water and contain much less proteins, usually less than 2% as compared with 8-12% in cereals. They also have lower contents of minerals and vitamins, and are thus limited in their contribution to the provision of a balanced diet.

In general, the cereal group and the fleshy fruit/tuber group constitute the largest portion of the typical African diet. These two groups of foods, especially the latter, because of their limited contribution to the provision of a balanced diet, should always be, and are in fact, usually, consumed with the typical African sauce. The African sauce is an extra-ordinary mixture of all sort of ingredients, including vegetables, tomatoes, peppers and spices, salt and magi (mono-sodium glutamate) cubes, meats, mushrooms, seed meals and several other condiments. This sauce thus serves as an important source of proteins, vitamins and minerals of reasonably high quality when consumed with the staple foods.

Fruit/Vegetable Group

: The term ‘vegetable’ is used to include some fruits (e.g. tomatoes and pumpkins), leaves (e.g. spinach and cabbage), roots (e.g. carrots), and even stalks (e.g. celery), and flowers (e.g. cauliflower). A wide variety of fruits grow wild or are cultivated. The contribution of this group of foods is the provision of nutritionally important quantities of water-soluble vitamins, especially folic acid and ascorbic acid, carotene (the pre-cursor of vitamin A), and minerals. Furthermore, many members of this group make substantial contribution of roughage to the diet in the form of cellulose. But the fruit members have low protein content which, though often ignored, may not be negligible. When Hippocrates formulated the maxim, ‘ thy food shall be thy remedy,’ he certainly must have had in mind the medicinal qualities of vegetables. The common fruits include mangoes, papaw, guava, coco-nuts, oranges, grape-fruit, tangerines, bananas, pine-apples, African pear, wild mangoes (oro, agbono or apon), pitanga cherry (agbalumo), local and imported apples, cashew fruit, avocado pear, cantaloupe and water melon. On the other hand, the common vegetables include spinach, pumpkin leaves, bitter leaves, water leaves, collard greens, sweet potato leaves, cassava leaves, mushrooms, onions, okra, carrots, tomatoes, cabbage and lettuce. Unfortunately, many of these are still regarded only as optional supplementary foods, perhaps because of their seasonality and relatively high cost and low caloric density.

In concluding this segment of the discussion, it is pertinent to state that there is currently no food grouping in use that does not have its own limitations. For example, foods like alcohol and alcoholic beverages (mostly used at social gatherings but which should not be allowed to replace or crowd-out proper food intake), carbonated drinks (consisting of sugar, water and flavorings), sugar, cooking oils, margarines and several other components of the African soup, which are either high in fats and oils or sugar, but low in other nutrients have not been classified and have been left out of this classification. Some of these items are sometimes referred to as “empty-calorie” foods. They are said to be empty-calorie foods because they do not meet our definition of a food that must contain other essential nutrients even when it has a preponderance of a particular nutrient.

Thus, the classes of foods available to a particular population or in a community may not easily be amenable to any one-classification method, as in this case. It should also be noted that not all food items available in a complex multi-national country like Nigeria are accommodated by this classification since these do not usually follow the nutrient pattern of any one of the Five Food Groups. This classification has not been designed to accommodate such food items. The foods of certain ethnic groups within the society may not meet any reasonably simple classification, and these have been left out. Despite these limitations however, this classification is simply a rough but good system which allows consumers and health workers make a quick and easy evaluation of the intake of essential foods in order to plan a diet or the food needs of a nation or a community which offers the basic nutrient requirements for optimum health.