**9. Bioactive constituents and their effects on diabetes**

appropriate nutrient intake is an integral part towards achieving the goals of dietary recom‐

**8. Problems associated with use of medicinal plants/traditional medicine**

WHO reported that in several countries and areas, about 80% of the third world countries and 40-60% of total world population use traditional medicine instead of orthodox medicine for health-care. The process of extraction and purification of plant extracts affect the unit cost [3]. These expensive products are unaffordable for the low income countries. The low demand for drugs led to the use of medicinal plants as herbal components of health foods and for preven‐ tive medicine. This new expanding market gave rise to nutraceuticals (nutriceuticals). Culhane [5] reported nutraceuticals as "foods derived from a naturally occurring substance (in pills or powder or other medicinal forms), which can and should be consumed as part of the daily diet, and serves to regulate or otherwise affect a particular body process when ingested". These foods are known as medicinal foods, phytofoods, phytonutrients and functional foods. All of these terms meant substances that may or may not be considered as foods or parts of food but provide health benefits when eaten. However, more people prefer traditional medicine. This is because it provides holistic treatment (treatment that caters for the spirit, body and soul). The need for traditional medicine arose from the indigenous knowledge. This showed that aetiology of diseases does not only come from physiological imbalance and psychological causes as in orthodox medicine, but can come from spiritual causes, astral influence, esoteric causes and imbalance in cosmic natural forces. This could be associated with the belief by some diabetic patients that their condition is diabolical (personal communication). Every region has had, at one time or the other in its history, a form of traditional medicine. However, distinction exists between the use of traditional medicine and traditional plant foods as regards thera‐ peutic agents used in diabetes management and health promotion. The misconception in the use of these indigenous medicinal plants precipitated self-medication when such plants are used. This poses serious problem in diabetes control in Nigeria. Consumers take medicinal plants, herbal products and nutraceuticals as food and think they are safe at any dose. Concerns raised about the interaction between herbal preparation and drugs are that herbal remedies might – i) increase the effect of an antidiabetic drug and plunge blood sugar to dangerously low level; ii) decrease the effect of blood pressure medication and cause high blood pressure and stroke; iii) decrease the effect of an anti-infection agent, letting the infection get out of control; iv) increase or decrease the effect of a blood thinner such as warfarin and cause either bleeding episode or formation of a dangerous clot. The combination of orthodox and tradi‐ tional medicines has negative impact on people with diabetes in Nigeria. This may explain high incidence of cases of uncontrolled diabetes and associated complications in patients admitted in hospitals in Nigeria. The major link between the use of traditional medicine and traditional plant foods is that their uses are community-based and indigenous. Each com‐ munity has its own peculiar approach to health and diseases even at the level of ethno-

mendations.

**and diabetes control**

70 Antioxidant-Antidiabetic Agents and Human Health

Several terms have been used to describe the therapeutic potentials of plants. Health-promot‐ ing activities, bioactive constituents, medicinal properties (often used in orthodox and traditional medicine), natural plant products and biological response modifiers are examples of such terms. All plants, especially the wild ones, are potential sources of biological active molecules. These compounds protect plants against predators and other damage but are not directly essential for growth. They are known as secondary chemical compounds or metabo‐ lites. The plant constituents useful extractable substances in their storage organs (leaves and seeds/roots) in quantities sufficient to be economically useful as raw materials for various scientific technological and commercial applications [3].

Some plant constituents appear to be disease specific. The plants for consideration when a hypoglycaemic property of a plant is elucidated were reported. Ivorra et al. [28] studied different compounds isolated from plants with attributable hypoglycaemic activity. They gave a broad classification as follows: polysaccharides and proteins; steroids and terpenoids; alkaloids; flavonoids and related compounds. Drewnowski and Gomez-Carneros [29] and Noor et al [23] reported phenols and polyphenols, flavonoids, isoflavones, terpenes and glucosinolates in vegetables and fruits; Thompson et al. [79] included phytate in bean flour, which reduced GI. Iwu et al. [80] found alkaloids in yam. Several studies have published similar effects with dietary fibre (non-starch polysaccharides, NSPs) [31, 73]. A new classifi‐ cation of dietary fibre (water-soluble and insoluble dietary fibre) was based on their solubility characteristics [81]. The soluble dietary fibre is highly viscous and has added viscosity as functional property in the evaluation food/diets. These NSPs lower blood glucose level by impeding glucose absorption from the gastrointestinal tract and reduce post-prandial hyper‐ glycaemia. The water-insoluble NSP are mainly obtained from structural carbohydrates (cellulose and lignin of cell walls) of starchy roots/tubers and cereals. The water-soluble NSP are obtained from storage carbohydrates (gum and hemicellulose) of legumes and as pectin from fruits and vegetables. The phytochemicals are basically sourced from fruits and vegeta‐ bles.

Widely used parameters for clinical studies in diabetes are post-prandial blood glucose, glycaemic index (GI) and glycaemic load (GL). Jenkins et al. [82] introduced the concept of GI to classify both single foods and mixed meals on the basis of their potential for increasing the blood glucose concentration. The starchy foods have high GI (>70%) compared to the low values (<50%) for vegetables, fruits, legumes. The GL is defined as the product of the amount of available carbohydrate in a certain amount of food and its GI divided by 100 [83]. Low GIbased diets tend to maintain glucose and insulin at a moderate level avoiding the hypergly‐ caemic state [84]. This is based on advantages of the GI concept: i) GI and GL are determined both on single and mixed meals; ii) they permit proper selection and combination of low and high GI foods to achieve good glycaemic control and prevent hyperglycaemia; iii) they prevent fear of excessive intake of low or high GI foods and resultant hypoglycaemia/hyperglycaemia; and iv) hyperinsulinaemia is abated when both GI and GL are considered in dietary counsel‐ ling. The link between GI and GL simply means that although both GI and GL elicit information on carbohydrate content of foods in relation to their blood glucose response. GI is associated with the quality of carbohydrate in a food/meal while GL relates to the overall quantity of carbohydrate in the same food/meal [85]. However, when these low GI (low GL) foods are habitually consumed in large amounts, high glycaemic effect may manifest over time. Based on this, attention is drawn to researchers on the limitation of the use of glycaemic index values alone in diabetes management. The practical application of the Gl, used in combination with other information on food composition, is promising in guiding good food choices, especially for people with diabetes. Englyst et al. [87] proposed the inclusion of rapidly digested starch (RDS) and slowly digested starch (SDS) to account for limitations of GI. More recently, resistant starch (RS) has received attention as one of the components of carbohydrate foods that are closely linked to glycaemic control [86]. Salijata *et al*. [34] observed that the justification of similarity of RS with NSP is that RS assays as insoluble fibre and has the physiological benefits of soluble fibre. They reviewed the importance of high amylose content and high amy‐ lose:amylopectin ratio in foods/diets in the post-pandrial glycaemic and insulinaemic respons‐ es. A higher amylose lowers digestibility of starch due to positive correlation between amylose level and formation of RS [88]. Plants with these hypoglycaemic activities collectively exert their effects in two major ways. They either improve insulin sensitivity to glucose at the peripheral cells to increase glucose uptake and reduce hyperglycaemia. Or, they act on insulin production-related actions to improve insulin production and control of blood sugar homeo‐ stasis.

**10. Documentation of anti-diabetic potentials of selected Nigerian**

The 1978 Alma Ata declared that traditional medicine is the surest means to achieve total health care coverage of the world's population. This has encouraged the use of medicinal plants. Currently, the active ingredients in most plants with anti-diabetic potentials are elucidated pharmacologically. Consequently, it was a bit difficult to identify edible Nigerian indigenous plants from huge database on medicinal plants. Information on their constituents of nutritional importance was lacking. Invariably, not all traditional medicinal plants qualify as plant foods. Bosch et al. [91] as cited in Ogbu et al. [92] reported that the total number of species of edible plants in primary use in Africa is 1004. However, a little above 50% of the number of medicinal plants was reported as 1975. In Nigeria, Federal Environmental Protection Agency (FEPA) shows that 20 species of the plants were in extinction since 1950. Another 431 species are endangered, 45 species are classified as rare, 20 species are vulnerable and 305 species are endemic [93]. Not all plants with antidiabetic potentials published online may be available or edible in Nigeria. The local herbalists keep secret the information on health benefits of indigenous crops to enhance their patronage. Preliminary identification of the anti-diabetic potentials of these plant foods becomes necessary to improve their food diversification and

Anti-Diabetic Effects of Nigerian Indigenous Plant Foods/Diets

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

73

Surveys on traditional food systems are commonly used to document information on indige‐ nous foods with health-benefits [94]. Google search was used to review literature on published works on ethnobotanical surveys in northern and southern regions of Nigeria. These were used to identify commonly consumed indigenous plants. Some related unpublished works were also used to supplement published data. Information obtained include botanical names of the plant foods where available, habitat (cultivated (C), wild (W) or semi-wild (S)), part used, culinary uses, anti-diabetic potentials/effects of single foods and diets and corresponding references. From the profile of edible indigenous plant foods, those that have antdiabetic potentials were selected based on their bioactive constituents, proven to be active ingredients in attenuating post-prandial blood glucose. Additional information on anti-diabetic effects of some of the plant foods/diets evidenced by *in vivo* or *in vitro* studies were also elucidated.

The concept of food groups of plant origin was used to present the results on documentation of Nigerian indigenous plant foods and those with anti-diabetic potentials. This was to encourage increased diversification and culinary uses. These food groups include fruits, vegetables, spices and condiments, grain legumes, nuts and oil seeds as well as starchy roots/

**indigenous plant foods**

consumption.

**12. Results**

**11. Sequence for literature review**

Evans et al. [60] has reported that pathogenesis of diabetes is better appreciated and should be discussed in line with hyperglycaemia and elevated free fatty acid in the blood in relation to oxidative stress and production of free radicals. Some plants with hypolipidaemic activities were included by several authors as those that may assist in diabetes control. This is because diabetes and cardiovascular disease are closely related. The active ingredients identified *in vivo* for this purpose are antioxidants (vitamin A, beta-carotene, vitamin E and tannins) [89, 90]. The degree of these constituents in foods and their relative importance varies with the chemical compound, specie, part and age of the plant as well as environment. From the above perspective, the following operational definition will be used for documenting the antidiabetic potential/effects of identified plant foods. *Anti-diabetic plant foods/diets* are those plant foods/ diets that contain any of the chemical compounds, shown to reduce hyperglycaemia or induce hypoglycaemia through their effect on the improvement of insulin resistance or insulin supply to the peripheral cells.
