**2. Plant foods in human nutrition and health**

uals, households and communities. The use of plant foods for therapeutic purposes represents one of the biggest human uses of the natural flora of the world [3]. This is because of their health-enhancing bioactive constituents [4]. In the last four decades, there has been consider‐ able interest in resurrecting health-promoting potentials of indigenous plant foods in devel‐ oping countries and integrating their use into modern medical system. The reasons for this interest are varied and include, i) the negative impact of nutrition transition that increase epidemic of diet-related non-communicable chronic diseases (NCDs) in such regions; ii) high cost of medicare, which put modern health care out of reach of the poor; iii) low adherence to drug prescriptions; and iv) side effects of medicinal plant and herbal medicine extracts and/or preparations, because out of ignorance the consumers consume them as food supple‐ ments that are safe at any dose. This is not true for any of the high biologically active medicinal plants. Most of them cannot be consumed habitually as local foods without adverse effects. There was need to challenge reduced interest in and demand for drugs amidst poor health management in these poor regions. Pharmaceutical preparations from medicinal plants created a new expanding market as herbal components of health foods and preventive medicine under "nutraceuticals" or "nutriceuticals". Culhane [5] defined them as products produced from food and sold in pills, powders and other medicinal forms not generally associated with food and are shown to have a physiological benefit or provide protection against chronic diseases. Chronic diseases are largely preventable diseases. Diet-related NCDs are diseases of long duration and generally slow in progression [6]. They are relatively difficult to manage. The high cost and side effects of these supplements still limit their use and have made this approach an unsustainable alternative strategy for chronic disease management and

Carbohydrate food sources form the greatest percentage [50-60%) of the daily diet for different segments of the population [7]. In Nigeria, starchy staples (cereals, roots/tubers) and legumes constitute the major part of the traditional diets, up to 70% and 25%, respectively [8, 9, 10]. Physiologically, chronic restriction of carbohydrate–rich sources, mainly supplied by plant foods, may pose a serious threat to Nigeria's survival. Diabetics are particularly adversely affected due to misinformation and inability to seek dietetic intervention. Such dietary misinformation has led to starvation and the development of psychosocial problems in diabetics. This is because they feel denied and full of anxiety in anticipation of lifestyle changes

Type 2 diabetes is more common in Nigeria. There was increase in the average prevalence rate from 2.7% [12] to 3.9% [13] and annual increase of 0.3%. Over the years, diet was implicated both as one of the aetiological factors to the development of diabetes [14] as well as a key component in diabetes management [7, 15]. Plant foods are the most important dietary sources to meet the nutritional needs of majority of the population in sub-Saharan Africa and Asian subcontinent [16]. Dietary fibre is a component of carbohydrate in plant foods shown to modulate post-prandial blood glucose after discovery of the "dietary fibre hypothesis" by Cleave [17] and Burkitt et al. [18]. Roles of phytochemicals and antioxidant constituents of plant foods were reported [4]. On this basis, plant foods hold good promise for diabetes

prevention.

60 Antioxidant-Antidiabetic Agents and Human Health

[11].

Plant foods have remained the ultimate source of nutrients for larger population of the world. They are simply described as irreplaceable food resources for humans, which exclude animal sources. Besides, they are available, affordable and acceptable. They are used for socio-cultural, diabolic, nutritional and therapeutic purposes. These foods contain many chemical com‐ pounds needed for metabolic functions in varying proportions. Some of these chemical compounds are non-nutrients that are beneficial to man and others provoke some adverse reactions depending on the levels of intake, interrelationships of nutrients and food habits. Plant foods are classified as cereals, roots and tubers, legumes (pulses, oil seeds and nuts), vegetables and fruits [25]. In order to accommodate these various constituents in foods provided by plants foods, three main categories were established according to the major nutrients they provide. They include the macronutrients (carbohydrate, protein, fat and water), micronutrients (minerals and vitamins) and non-nutrient components (dietary fibre, phyto‐ chemicals, anti-nutrients, food toxicants and additives). Metabolic functions of these nutrients and non-nutrients were reviewed by several authors. Bennett [16] observed that plant foods provide the bulk of daily calories for humans [85%) and about 65% of the protein, an assortment of minerals and vitamins, unsaturated fats and phytochemicals in a characteristic manner that reflects current dietary recommendations aimed at promoting health and reducing diet-related chronic diseases. Thomas [26] concluded that the contribution a food makes to nutrient intake of a person depends on the quantity consumed per 100g, the amount consumed per meal and the frequency of consumption.

**3. Plant foods utilization in Nigeria**

wild or are semi-wild.

Nigeria's diverse ethnic groups (over 250] are accommodated under three main ethnic regions - Igbo (in the East), Yoruba (in the West) and Hausa-Fulani (in the North). The country has a beautiful climate, which endows it with very rich biodiversity. A variety of plant foods (maize, rice, sorghum, millet, yam, cassava, cocoayam and legumes) are mainly produced as subsis‐ tence food crops in Africa. They are more commonly and widely consumed in Nigeria and other developing countries than in the developed world. They are relatively available, affordable and acceptable. They contribute appreciably to the nutrient intake (energy, protein, fat, vitamins and minerals) of the less developed world. In Nigeria, starchy staples (cereals, roots/tubers) and legumes constitute the major part of the traditional diets (up to 70% and 25%, respectively) [8]. However, cereals are the major staples in the north with much higher intake of animal protein sources (mutton, beef and milk), while starchy roots and tubers are the main staples in the south with relatively more consumption of legumes [10]. These foods contribute appreciably to nutrient intake of southerners [36]. The plant foods are cultivated, gathered

Anti-Diabetic Effects of Nigerian Indigenous Plant Foods/Diets

http://dx.doi.org/10.5772/57240

63

Roots and tubers are the thickened underground starch storage organs of some plants, propagated vegetatively from the underground stems and their stem cuttings. These edible roots and tubers belong to several families and are formed by both monocotyledons (yams and cocoyams) and dicotyledons (cassava and sweet potatoes) [37]. Cereals are seeds of grass family (Gramineae). Cereals are important crops which serve as industrial raw materials and staple foods for the world over [38]. Cereals are the most widely cultivated and consumed crops globally. World cultivated cereals include wheat, maize, rice, barley, oats, rye, sorghum, millet, wild rice and hungry rice (acha). In Nigeria, the starchy staples (maize, rice, sorghum, millet, yam, cassava, cocoayam and plantain) are utilized in many different forms for prepa‐ ration of various dishes. Their nutritional importance is that they provide most of the energy, contain high carbohydrate, low protein and appreciable amount of minerals and vitamins, especially the B-complex vitamins. They form the base and usually constitute the major ingredients in the traditional dishes. Some dishes are light and serve as breakfast. Others are solid and frequently made palatable in combination with a variety of legumes and by the addition of palm oil, vegetables and fruits, a range of spices, various sauces and fish/meats. They serve as main meals and eaten later in the day. Processing and preparation methods of these starchy staples and their recipes vary with ethic groups and geographical locations. Each of these staples irrespective of the preparation methods produces a thick paste known as "foofoo" eaten with soups/sauces. These dishes are highly cherished and consumed daily in all parts of Nigeria [39]. These starchy staples are also used to produce complementary foods and local snacks as roasted/fried/baked products or drinks. Some like yam, cocoyam, 'okoho'

Legumes are flowering plants in the family Fabaceae (or Leguminosae) that have pods, which contain beans or peas. According to Okafor [40], a list of edible woody leguminous plants, consisting of 150 species covering 103 genera in 48 families was recorded in Nigeria. Legumes rank second to the grasses as source of fodder (for animal) and food for man. The plants are most commonly known as pulses, peas or beans [38]. They contain more protein and less carbohydrate than cereals. There are two main types of legumes: those containing high protein

(*Cissus pulponea* root) are also used to thicken traditional soups.

Obviously, plant foods have other values related to human nutrition and health apart from their nutritional importance. Plant foods are one of the elements in virtually all cultures, with symbolic and ritualistic values that link language and religion. In many cultures, especially the Asian countries, distinction between food and medicine as therapeutic agents is obscure as the traditional vegetable diets provide the people with disease fighting arsenals that serve both protective/preventive and curative functions. For this reason, foods are widely recognized as the primary health provider.

The bioactive compounds or secondary metabolites are the non-nutrient components in plant foods. They have some nutritional effects and health benefits. They are those substances contained in foods which supply no nutrients. They could contain some compounds that are beneficial to health or toxic to humans and/or act as antagonists to nutrients in foods [27]. They include tannins and other phenolic compounds (phenols, flavonoids, isoflavonoids), saponins, glucosinolates, alkaloids [28, 29], phytate and dietary fibre [30]. These chemical compounds are found in different classes and parts of plant foods in varying amounts. They are more concentrated in plant storage organs (leaves and seeds) than other parts of the plants [22]. These constituents have their individual health-promoting qualities that compel people to combine the different food sources to achieve healthy eating and maintain good health. Several authors [27, 31-35] studied therapeutic potentials and metabolic effects of foods rich in dietary fibre and phytochemical constituents. These include lower risk of colon cancer, promotion of early satiety and normal laxation, moderation of post-prandial blood glucose responses and improved insulin sensitivity, reduction in total and low density lipoprotein (LDL)-cholesterol, regulation of appetite and enhancement of sodium and fluid balance. They are also used to treat constipation and prevent development of diverticulosis and diverticulitis. These are features of a dietary pattern to treat and prevent obesity and its co-morbidities (especially type 2 diabetes mellitus). These two conditions are closely linked because hyperglycaemia and hypercholesterolaemia are well-known cardiovascular risk factors in type 2 diabetes mellitus. Invariably, diets adequate in dietary fibre are usually rich in micronutrients and phytochem‐ icals, and frequently less calorically dense and lower in fat and added sugars. However, environmental factors, cultural food habits and insufficient nutritional information about health benefits of traditional plant foods still pose a problem to healthy food choices. Drew‐ nowski and Gomez-Carneros [29] reported that most of the bioactive compounds are bitter, acrid or astringent and aversive to the consumer and may be wholly incompatible with consumer acceptance. These caused increasing epidemic of diet-related diseases across the regions. They suggest the need to take sensory properties and food preferences into account when advocating for increased consumption and diversification of rich sources of these secondary metabolites in plant foods. The challenge of achieving adequate supply of energy and nutrient intake as well as the health-promoting compounds from plant-based foods/diets without compromising the health of an individual, forms the basis for current dietary recom‐ mendations aimed at promoting consumption of plant foods to reduce diet-related NCDs.
