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Classification of Nigerian foods: A review
Department of Epidemiology and Community Health, University of IIorin, IIorin, Kwara State, Nigeria
The range of various tropical climates supports a wide variety of foods throughout the West African region, and indeed all of sub-Saharan Africa. The ability of people in this region to feed themselves depends to a large extent on the adequacy of moisture or water supply. Where the water supply can support plant growth, it is possible to raise as many as three crops a year. For example, in Nigeria, which is the most thickly populated country in this region, the driest northernmost regions are capable of supporting the cultivation of livestock and cereals, such as wheat, rice, maize, millet, and guinea-corn The wetter middle-belt regions support the cultivation of legumes and livestock, and the southern, typically tropical regions of the country support the cultivation of tree crops as well as tubers and roots but relatively little livestock production. Throughout Africa, food choices are restricted not only by climate but also by serious problems of communication, transportation, and storage.
Within these limitations, the ultimate choice of food by the consumer is a very personal one. In a country like Nigeria, where the consumer's knowledge of nutrition and food and the resources for making a wise choice of the latter are all rather limited, it is instructive to set out guidelines to aid consumers to make nutritionally advantageous choices. A number of guidelines have already been developed, among which are the recommended dietary allowances (RDAs) and the "basic four food groups" (BFFG). The object of this paper is to discuss the characteristics and purposes of some major food classification systems as they have developed historically and to develop a system that is appropriate to the socio-economic, geographic, and cultural conditions that obtain in sub-Saharan African countries.
The RDAs, which represent nutritional standards for planning and assessing dietary intake, have been defined by the Food and Nutrition Board of the American National Research Council as the "level of intake of the essential nutrients considered to be adequate to meet the nutritional needs of practically all healthy persons" (6). The BFFG system, on the other hand, constitutes a food grouping or classification used to translate nutritional needs as established by the RDAs into practical guidelines for actual food intake (4). This food grouping is determined, first and foremost, by the nutrient content; the BFFG system reflects the availability of food, food patterns, and local nutritional problems (4, 23). Thus, the grouping together of foods with similar nutrient density and nutrient content makes it possible to choose from a wide variety of alternatives if certain seasonal foods become scarce or money is short (23).
The History of Food Classification
In 1834 William Prout, an English physician, was the first scientist to classify foods by grouping them into "foods of an animal or albuminous nature, foods of a vegetable or saccharine nature and a group of fatty or oily foods" (5). The modern system of classification was developed during World War I because there was a considerable interest in the dissemination of information on food and nutrition at that time. The work of Hunt (10) around 1921 may have contributed in no small measure to this effort. The main theme of systems of the World War I era was that all foods could be divided into a small number of categories, members of which could be interchanged. These early guides were general in nature and did not attempt to evaluate nutritive contributions within a group. They were intended to serve as educational guides for the selection of foods and the planning of meals. For example, the term "protective foods," meaning milk, eggs, and vegetables, was coined by McCollum in 1918, when the "body-building" as well as the "protective" values of these foods had not been completely elucidated. The use of modern dietary standards are, therefore, an innovation of comparatively recent times, established first in 1936 through the League of Nations, based on the limited knowledge of nutrition at that time (5).
Food rationing during World War II provided an impetus for the development of a new classification system, and in 1943 the "Basic Seven" food guide was promoted as a means of selecting alternatives to common foods that were in limited supply After the war the "Basic Seven" guide was reviewed, and a revised version, known as the "National Food Guide," was adopted in 1946 (5). The most recent food guide appeared in 1955; it was based on the 1946 version and was called "Food for Fitness: A Daily Food Guide." This guide contains the basic four food groups classification already adopted by the United States and Canada.
THE BASIC FOUR FOOD GROUPS
The BFFG system is a simple device used by nutritionists to outline the variety of foods needed for a balanced diet that provides the essential nutrients (22). The food groupings are:
1. the milk group - comprising all dairy products,
such as powdered milk, skim milk, fresh milk, buttermilk,
condensed milk, ice-cream, and yoghurt;
2. the meet group - including diverse food items such as beef, veal, lamb, pork, other meats, eggs, fish, beans, peas, ground-nuts, and other nuts and seeds;
3. the cereal and grain group - including wheat, rice, maize, guinea-corn (sorghum), millet, and potatoes;
4. the fruit and vegetable group - including all fruits and vegetables commonly consumed.
This classification system does not contain several food items commonly consumed in Nigeria but includes most foods consumed in the United States and Canada. In most parts of Nigeria, as in most parts of Africa, the poor economy, the socio-cultural factors, and the geographical location and distribution of food have combined to limit the food choices of families (5). Queen (21) has pointed out that in less-developed economies people subsist on whatever food is available to them, including squirrels, lizards, and camel and horse meat (7). Furthermore, food items such as edible caterpillars, termites and other insects, snails, and locust beans, which may not be regarded as food items in the advanced nations and therefore do not appear in their list of food items, are often regarded as delicacies or regular staple food items, depending on the economic status of the consumer. In the advanced nations, there is a strong reaction to the eating of lizards, dogs, and insects because such practices violate people's sensibilities (5).
In the more advanced economies, foods are processed and enriched, thus enlarging food choices. Moreover, several processed foods have found their way to the African table, such as Semovita, instant fufu powder, and instant yam powder (15). Such new processed foods are more amenable to modifications and enrichment than their traditional counterparts and are, therefore, expected to improve the nutritional status of the people.
The BFFG classification of foods, despite its minor limitations, has the major advantage of being a very simple device. People more easily remember a few basic food groups than a more complicated system (5). Simplicity is an especially important consideration in a country like Nigeria, where the level of education is limited. Thus, a classification system most appropriate for African countries with food choices similar to Nigeria's should be as simple as the Americo-Canadian classification system but encompass the variety of foods characteristic of African cultures.
THE PRESENT STATUS OF FOOD CLASSIFICATION IN NIGERIA
In most health institutions in Nigeria, foods are still classified according to the functions they are supposed to perform, perhaps in compliance with the Federal Government's Nutrition Curriculum Guidelines (16). Thus, foods are classified as "energy foods," "body-building foods," "protective foods," or "accessory food substances," very much in line with the early classifications of Hopkins and McCollum (5). Such classifications are obviously obsolete, inapproproate, or even misleading. Practically all common foods offer at least two or more nutrients (table 1), and thus, each contributes substantially to the overall nutritional balance of the individual and also performs several functions.
From table 1, it is obvious that no single food contains all the nutrients needed by the body in amounts sufficient to maintain life and promote optimum growth. Nevertheless, each food item supplies significant amounts of two or more nutrients. Therefore, almost all foods offer bodybuilding, energy-producing, and protective properties depending on their quantities and qualities (nutrient densitites) and the physiological state of the individual consuming them (4). For example, while eggs, meat, and milk might offer excellent proteins (body-building qualities), they (especially meat) also provide substantial amounts of energy derived from their fat content as well as from their proteins. They, therefore, provide greater potential energy than the so-called carbohydrate energy foods. Furthermore, the protein in meat may not be used primarily for tissue synthesis or for growth unless and until the energy requirements of the individual are met. Fat, which serves primarily as an energy reservoir in concentrated form, is also required for (a) the assimilation of other nutrients, especially the fat-soluble vitamins, and (b) the synthesis of several essential compounds in the body, including cholesterol, prostaglandins, testosterone, and other lipid-containing hormones and compounds, which are constituents of the normal body structures. Thus, fats are very important in terms of the structure and protection of the body from physical and physiologic damage.
The nutritional contribution of a given food is not limited to one category of nutrients. Milk, for example, supplies a significant amount of the daily requirement for protein, calcium, and niacin. Bread, rice, and maize each contribute mainly carbohydrates, in addition to substantial proportions of the daily protein requirement, especially when large quantities are consumed. Furthermore, when each of these foods which are limited only in Iysine and the sulphurcontaining amino acids, is combined with a legume, the resultant diet, together with the typical African sauce, constitutes a very important source of proteins of reasonably high quality, as well as vitamins and minerals. It has been estimated that the so-called starchy energy foods, such as the cereals, provide more than 50 per cent of the protein requirements of a normal human diet (24). Thus, it is the combined effect of all the nutrients in the diet that is important, and a wide variety of foods can contribute to this balance.
TABLE 1. Proximate Composition of Some Popular Nigerian Foodstuffs
|Fish (raw mackerel)||19.0||?||1.8||64||1.3||8.8|
|Locust beans(dawadawa or iru)||39.7||?||31.4||365||41.5||2.4|
|Melon seeds (egusi)||28.4||?||52||354||8.1||35.4|
Adapted from information in references 11, 17, 19, 20, 21, and 24.
Uddoh (23) has classified Nigerian foods into twelve groups. This grouping puts legumes, nuts, seeds, eggs, meats, poultry, and fish into four separate groups. But on the basis of the nutrient density of each of these food items, one could safely place all four in one group. For example, the similarity in protein content of these foods, shown in table 1 above, makes it possible to place all these food items in one group. These items, however, also contain generous amounts of carbohydrates, fats, and calcium. Based on the dietary contribution of nutrients by food items, the following groupings are suggested for Nigeria and other African countries with similar socio-economic settings, geography, and eating patterns.
A FOOD CLASSIFICATION FOR NIGERIA
Group One - Milk and Milk Products
This group is made up of all dairy products, including fresh milk, skim milk, buttermilk, condensed milk, powdered milk, local and foreign cheeses, butter, yoghurt, and icecream. Individuals with varying degrees of lactose intolerance have a choice of cheeses, buttermilk, and yoghurt. However, for those who must watch their weight, the use of ice-cream and other milk-containing beverages should be restricted. This group is valued particularly for its calcium, magnesium, riboflavin, cobalamin, and high-quality protein but is notably low in iron and ascorbic acid.
Group Two - Meats, Fish, Nuts, and Beans
This group includes meats; poultry; fish; snails; shrimp; termites; grubs; edible insects, such as caterpillars, locusts, crickets, and grasshoppers; crabs and other sea products; eggs; legumes (pulses); seeds; and nuts (22, 23). Although the nutritional contributions of the members of the group vary, they all provide valuable amounts of energy, protein, iron, and B-complex vitamins. The various cuts of meat do compare favourably with the amounts of protein available in poultry or fish. While legumes contain only about 30 per cent of the amount of protein available in animal protein foods of equivalent weight, other valuable components of the various foods in this group compare quite favourably with meats, particularly in light of the high cost and the variable prices of the latter (22). Furthermore, since large amounts are consumed, legumes are perhaps the most important sources of proteins in many African diets (1, 2, 18), partly because they are relatively cheap, palatable, and keep fairly well (9). Thus, eggs and legumes can be used freely to replace the higher-priced cuts of meat without sacrificing nutrition (8). Furthermore, 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 per cent saturated fat, compared with poultry and fish, which contain 6 per cent and 2-8 per cent respectively) (8).
Group Three - Cereals and Grains
The separation of cereals and grains from the tubers, roots, and starchy fruits is based on the differences in their ease of storage (3) and protein content (8). Although they are of plant origin, the group-three foods contribute not only carbohydrates but also the B-complex vitamins, iron, magnesium, and generous amounts of protein and energy to the diet (8, 9). Members of this group include bread and other wheat products such as Semovita, rice, maize, guineacorn, and millet. It is believed that there is hardly any village in Africa where one cereal or another is not used as a staple (9). As a group, cereals constitute the most important food for peoples all over the world (23), with approximately half of the people in the world depending heavily on rice. The survival of the peoples of the Sahel regions has been attributed to the use of cereals, limited only in Iysine and the sulphur-containing amino acids (9).
Group Four - Hoots, Starchy Fruits, and Tubers
The members of this group include yams, sweet potatoes, cassava, plantains, and breadfruit They are the common staples in the wetter, more humid regions of Africa ( 10), but they are readily perishable and cannot be stored for long periods of time. Because of storage limitations, they are seasonal foods (3). As a group, they are mainly starchy foods and major sources of readily available energy, with high caloric densities. They supply about 385 kilocalories per 100 grams of dry matter and very low amounts of other nutrients. Thus, they are limited in their contribution to the provision of a balanced diet (9).
Group Five - Fruits and Vegetables
This group provides nutritionally important quantities of the water-soluble vitamins, especially folic and ascorbic acids, carotene (the precursor of vitamin A), and minerals (8). Furthermore, many members of this group make substantial contributions of roughage to the diet in the form of cellulose (8). Fruits have low protein content, while the protein content of vegetables, often ignored, may be significant (19). The common fruits include mangoes, pawpaws, guavas, coconuts, oranges, grapefruit, tangerines, bananas, pineapples, imported apples, African pears, cashew fruits, avocado pears, and watermelon (3, 8). The common vegetables include turnip greens, mustard greens, kale, spinach, mushrooms, pumpkins, onions, okra, collard greens, bitter leaf, water leaf, carrots, tomatoes, cabbage, and lettuce (3, 8). Unfortunately, many of these are still regarded only as optional supplementary foods (3), perhaps because of their seasonality and relatively high cost.
In general, the group-three foods (cereals and grains) and group-four foods (roots, starchy fruits, and tubers) constitute the largest portion of the typical Nigerian diet. These two groups of foods, especially the latter, because of their limited contributions to a balanced diet, are usually, and should always be, consumed with the typical African sauce. The African sauce is an extraordinary mixture of many ingredients, including vegetables, tomatoes, peppers, oil, salt and Maggi (MSG) cubes, meats, mushrooms, seed meals, and several other condiments and spices. This sauce, thus, serves as an important source of proteins, vitamins, and minerals of reasonably high quality (9) when consumed with the staple foods as shown in table 2.
Limitations of the Classification System
Foods like alcohol, sugar, cooking oils, soft drinks, margarine, and several components of African soup, which are either high in fats and oils or sugar but low in other nutrients, have not been included in the five food groups described in this paper. Some of these items are sometimes referred to as "empty-calorie" foods (5), so called because a food must contain more than one essential nutrient.
TABLE 2. The Utilizable Protein Content of Some Staples and the Diets Based on Them
|Protein Content (ND cal %)|
Adapted from refs. 14 and 17.
Major Criticisms that may be levied against this classification are that (a) the nutritional needs of every individual in the population cannot be met by this classification; (b) not all food items available in a complex, multinational country like Nigeria are encompassed by this classification system since these usually do not follow the nutrient pattern of any one food group; and (c) the foods of certain ethnic groups within the society may not meet any reasonably simple classification, and these have to be left out.
Despite these limitations, the classification is a rough but good system that allows consumers and health professionals to make a quick and easy evaluation of the intake of essential foods in order to plan a diet that offers the basic nutrient requirements for optimal health.
I wish to acknowledge the valuable contributions of my colleagues Professor O. K. Alausa (Department of Epidemiology and Community Health, University of IIorin) and Dr. David Atte (Department of Geography, University of IIorin).
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