**1. Introduction**

Plants play important role in the cycle of nature. This is because life on earth basically depends on them. Plants provide man with all his needs as regards food, shelter, clothing, flavours and fragrance as well as medicine. They are naturally occurring substances that produce almost all the foods that animals as well as humans eat. They have unique potential to make their own food through photosynthesis. All foods that people eat naturally come directly or indirectly from plants. Food is fundamental to human survival. It is basic for averting hunger, satisfying one's palate and maintaining health of every human being. It is used as a status symbol, making people happy, emotionally and socially content, and constitutes a form of cultural expression. It is also used in the performance of various rituals and rites as well as for therapeutic purposes. Culture has a lot of influence on the kind of foods people eat and how they eat them. Traditional foods, was adopted to describe all foods from a particular culture, available from local sources and culturally acceptable as appropriate and desirable foods [1]. The direct and indirect food sources as regards nutrition are simply described as and categorized into two major sources plant and animal foods, respectively.

Despite the unique role of plant foods as irreplaceable food sources for humans, not all plant foods are available or edible worldwide. Traditional plant foods are those plants grown for food in varying proportions within the farming system operating in any particular locality; or gathered in wild or semi-wild conditions; and are accepted by the community, through custom, habit and tradition as appropriate and desirable foods [1, 2]. They are categorized as those that are consumed as traditional dietary staples and those consumed as components of accompa‐ nying relishes and sauces. These traditional foods are often used in sciences as basis for ensuring and optimizing utilization of indigenous foods and their health benefits by individ‐

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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 prevention.

management. There are mounting scientific evidence to date on their various health-promoting

Anti-Diabetic Effects of Nigerian Indigenous Plant Foods/Diets

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

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The global concern for the diversification of the uses of plant foods to improve normal and therapeutic nutrition for diabetes control has shifted scientists' interest to enhancing the potential sources of beneficial constituents in plant foods. Plant foods have generated increas‐ ing research interest because of their anti-diabetic potentials. There is need to integrate traditional plant foods within local research and innovative systems, in accordance with local needs, food habits and priorities. Currently, documentations on Nigerian indigenous plant foods with anti-diabetic properties are either scattered or lacking. Most reviews on antidiabetic potentials of plants both locally [19, 20, 21] and internationally [22, 23, 24] were done on medicinal plants. Evidently, not all medicinal plants and herbs used locally are edible. Similarly, not all identified food crops have anti-diabetic potentials. Most of the plants assayed pharmacologically present some difficulties in their dietetic application in humans. They create a gap in optimizing their health-promoting potentials. This paper focuses on some Nigerian indigenous plant foods with anti-diabetic potentials, parts used, their individual effects as reported *in vitro/in vivo* and the extent to which the elucidated parts of the plants were incorporated into the traditional diets for good glycaemic control. The scientific evidence for health benefits of the identified plant foods are summarized in tabular format, and the strength of the evidence is discussed in general terms. Optimization of the utilization of some commonly consumed indigenous anti-diabetic plant foods and their diversification would enhance good diabetes management, improve health of people with diabetes in Nigeria and offer more

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

sustainable health benefits for the indigenous inhabitants.

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

properties.

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 [11].

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 management. There are mounting scientific evidence to date on their various health-promoting properties.

The global concern for the diversification of the uses of plant foods to improve normal and therapeutic nutrition for diabetes control has shifted scientists' interest to enhancing the potential sources of beneficial constituents in plant foods. Plant foods have generated increas‐ ing research interest because of their anti-diabetic potentials. There is need to integrate traditional plant foods within local research and innovative systems, in accordance with local needs, food habits and priorities. Currently, documentations on Nigerian indigenous plant foods with anti-diabetic properties are either scattered or lacking. Most reviews on antidiabetic potentials of plants both locally [19, 20, 21] and internationally [22, 23, 24] were done on medicinal plants. Evidently, not all medicinal plants and herbs used locally are edible. Similarly, not all identified food crops have anti-diabetic potentials. Most of the plants assayed pharmacologically present some difficulties in their dietetic application in humans. They create a gap in optimizing their health-promoting potentials. This paper focuses on some Nigerian indigenous plant foods with anti-diabetic potentials, parts used, their individual effects as reported *in vitro/in vivo* and the extent to which the elucidated parts of the plants were incorporated into the traditional diets for good glycaemic control. The scientific evidence for health benefits of the identified plant foods are summarized in tabular format, and the strength of the evidence is discussed in general terms. Optimization of the utilization of some commonly consumed indigenous anti-diabetic plant foods and their diversification would enhance good diabetes management, improve health of people with diabetes in Nigeria and offer more sustainable health benefits for the indigenous inhabitants.
