**4. Diabetes and its public health importance**

[25-35%) and oil content [15-45%) and those containing moderate protein [18-24%) and less than 5% oil content. They are oil seeds and pulses, respectively. The most common forms in which legumes are used – they may be cooked alone as pottage, or eaten in combination with any starchy staple of choice. The more widely consumed legumes include cowpea, pigeon pea, soyabean, bambara-groundnut, african yam bean, groundbean and lima bean. It is due to their high protein content that legumes are widely used in combination with cereals for production of nutritious complementary foods for infants and young children both in Nigeria and other developing countries, in both industrial and household levels. This is because legumes are deficient in sulphur-containing amino acids (methionine and cystine) and contain high amount of lysine. Cereals are deficient in lysine and rich in the sulphur-containing amino acids. Legumes play very important culinary roles as soup thickeners. Many of the leguminous seeds are used for thickening soups, sauces and stews in Nigeria [41]. These soup thickeners are condiments/ingredients used in preparation of local soups to alter their consistency and give them special flavour [42]. Traditionally, roots/tubers (yam and cocoayam, 'okoho'), vegetables (okro, 'ogbamu' leaves), legumes (grain legumes/oil seeds and nuts) and fungi are used for thickening soups. Soups made from them are basically prepared with meat and/or fish (when available), oil, vegetables, crayfish, pepper and other condiments and water to obtain watery or thick consistencies depending on their composition. These soups are traditionally consumed in combination with cereals and starchy roots/tubers, processed into a form of paste known as "foofoo". Soups are very important accompaniment to main dishes in Nigeria. Ene-Obong et al. [39] recorded 110 soup recipes out of 322 recipes in all the 6 geo-political zones in Nigeria. The total number of recipes documented reflects the biodiversity of the Nigerian food system. The high viscous property possessed by these leguminous soup thickeners is associated with their dietary fibre content, implicated in attenuation of post-prandial blood glucose and control

Vegetables are succulent herbaceous plants that are harvested and eaten whole or in part, raw or cooked as part of a main dish or salad [43]. They can be classified into leaves (green, fluted pumpkin), stems/whole shoot (asparagus, elephant grass, 'achara'), roots (carrot), flowers, immature fruit (fresh corn, okra), mature green fruits (peppers), ripe fruit (tomato), fresh pod (vegetable cowpea), bulbs (onions), tubers (irish potatoes, yams) and fungi (mushrooms, puffballs). There are over 500 known edible vegetables in Africa. Some of these are valued for their bulking effect/thickening power and others may be used as garnishes or spices. Vegeta‐ bles are generally low in calories and protein. They are valued most for high vitamins and minerals contents. They are low in sodium and rich in potassium, which helps to lower blood pressure [44, 45]. They also contain dietary fibre and phytochemicals (pigments and other compounds that impart flavour to foods), which have heart-disease fighting properties. However, fruits and vegetables consumption is generally low in Nigeria despite their recog‐ nition as very important food items to reduce nutrient deficiencies from inadequate intake of

Composition of vegetables depends on their species, part of plant and stage of maturity. Spices are vegetables used as ingredients, which contribute to the taste and flavour of foods. The flavour of vegetables is due to sugars, organic acids, minerals salts, volatile sulphur com‐ pounds and tannins. The strong flavour of some vegetables (onions and cabbage) is due to their sulphur-containing compounds. Non-volatile acids such as malic, citric, oxalic and

of lipid metabolism [32].

64 Antioxidant-Antidiabetic Agents and Human Health

minerals and vitamins [46].

The term "Diabetes" has been defined by many authors from different perspectives. However, the similarity in these definitions is that diabetes is a chronic metabolic disorder, characterized by high blood glucose (hyperglycemia), associated with impaired carbohydrate, fat and protein metabolism, resulting from either insufficient or no release of insulin by pancreas in the body [48, 49]. Diabetes mellitus is a chronic life-long disease, which has been known to mankind for over 2000 years. It requires careful monitoring and control. Currently, diabetes ranks fourth worldwide among the NCDs (cardiovascular diseases, cancers, chronic respira‐ tory diseases and diabetes) with prevalence rates of 30%, 13%, 7% and 2%, respectively WHO [50]. It has been projected that by 2020 -2025, the number of people in the developing world with diabetes will increase by more than 2.5 fold; from 84 million in 1995 to 228 million in 2025 [7] and that 70% of deaths due to type 2 diabetes will occur in developing countries. Diabetes mellitus is increasingly being recognized as a major public health problem in developing countries.

Aetiological classification of diabetes mellitus includes type I diabetes (immune-mediated and idiopathic), type 2 diabetes, gestational diabetes and other specific types [48, 49]. However, types 1 and 2 diabetes mellitus appeared to have gained much more popularity among researchers and have generally been considered as the two major categories. In Africa, type 2 diabetes is the predominant form of diabetes in sub-Saharan Africa, accounting for over 90% of cases. The IDF Atlas [51] estimated that 10.8 million people have type 2 diabetes in sub-Saharan Africa in 2006 and this would rise to 18.7 million by 2025, an increase of 80%, as such exceeding the predicted worldwide increase of 55% [52]. In the past, the estimates on mortality of diabetes as the leading cause of death for sub-Saharan Africa were amongst the lowest for all regions globally [53]. This was attributed to Africa's rich biodiversity and high consumption of natural foods, which are rich in complex carbohydrates, proteins and dietary fibre.

There is enormous and escalating economic and social cost of treating type 2 diabetes. Sifelani [54] observed that the number of people seeking medical assistance for diabetes is rising in Africa at a time when health experts reported the continent's overburdened health systems are ill equipped to diagnose the disease. Majority of the poor cannot afford the cost of treat‐ ment. Cost of treating diabetes accounts for about 10% of the national income of most countries in Sub-Saahara Africa. National surveys in most parts of Africa indicate that diabetes cases are on the rise due to rapid urbanization as well as fast changing diets which are displacing the traditional ones in favour of the western diets [55]. This makes a compelling case for attempts to reduce the risk of developing diabetes.

stream, elevates blood glucose level. This rise in blood glucose stimulates the secretion of insulin from the beta-cells of the pancreas to regulate blood sugar levels by increasing active transport of glucose into fat and muscle cells. Post-prandially, blood glucose is absorbed and transported via the portal vein to the liver. The liver maintains blood glucose levels by converting glucose into glucose-6-phosphate and glycogen (glucogenesis). The increased insulin secretion from the pancreas and subsequent cellular utilization of glucose lowers blood glucose levels. Lower blood glucose level decreases insulin secretion. In diseased condition, insulin production is decreased to inhibit glucose uptake into the cells, which precipitates hyperglycaemia. The insulin secreted by the pancreas at this time is not used by the target cells. Hyperglycaemia is a common effect of uncontrolled diabetes and overtime, it causes serious damage to many body systems, particularly, the blood vessels and nerves. Common symptoms include glucosuria, frequent urination (polyuria), excessive thirst (polydypsia), excessive

Anti-Diabetic Effects of Nigerian Indigenous Plant Foods/Diets

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

67

hunger (polyphagia), sudden weight loss, extreme tiredness and blurred vision.

insulin resistance [62].

severity of diabetic complications [63].

Decreased amount of insulin in circulation decreases lipogenesis and increases lipolysis. Increased lipolysis releases fatty acids from adipose tissues. Fatty acids are also absorbed from the intestinal tract. The rapid release of fatty acids in the blood leads to hyperlipidaemia. The blood level of cholesterol increases, causing the development of atherosclerosis to occur at an earlier age than in non-diabetics and is more pronounced [61]. Elevated circulating levels of free fatty acids derived from adipocytes are the most likely link between insulin resistance and type 2 diabetes [60]. They contribute to insulin resistance by inhibiting glucose uptake, glycogen synthesis and glycolysis, and increasing hepatic glucose production. This leads to a decrease in intracellular concentration of glucose by a reduction in glucose-6-phosphate levels, implicating the glucose transport system as the rate-controlling step for free fatty acid-induced

Free radicals and enhanced oxidative stress with reduced blood levels of anti-oxidants were implicated in the pathogenesis of diabetes and more importantly, in the development of diabetic complications [60, 63]. Free radicals are highly reactive molecules (charged superox‐ ide, hydroxyl radical and nitric oxide). The uncharged hydrogen peroxide species is capable of damaging cellular molecules, DNA, proteins and lipids. These produce altered cellular functions. Oxidative stress is a serious imbalance between the production of free radicals and antioxidant defences. This causes potential tissue damage [64]. Antioxidants play protective role against the effects of hyperglycaemia and free fatty acids *in vitro*. They neutralize free radicals effects in experimentally-induced diabetes in animal models [60] and reduce the

**6. Dietary approaches to the management of type 2 diabetes mellitus**

A diet is a combination of foods individuals or community habitually eat to exist or live, or use for therapeutic purposes. Diet is known for many years to play a key role as a risk factor for chronic diseases [7]. Conventionally, type 2 diabetes is controlled with diet alone or diet and hypoglycaemic drugs (in combination with insulin in few cases where pancreas produces

Nigeria is among the top 5 countries that have the highest number of people affected by type 2-diabetes in sub-Saharan Africa. Nigeria has about 1.2 million people; South Africa, 841,000; the Democratic Republic of Congo, 552,000; Ethiopia, 550,000 and Tanzania, 380,000 living with diabetes. A national survey had an average prevalence rate of 2.7% with similar pattern in both sexes. There are slightly varying prevalence rates in different geographical locations [12]. Some sporadic figures on prevalence rates of diabetes in Nigeria were published. Cooper *et al.* [56] studied rural areas in Nigeria and found the prevalence of diabetics to be 2.8%. Wokoma [57] reported that the prevalence of diabetes in Nigeria ranges from 1% to 6%. International Diabetes Federation (IDF) [13] and [51] reported 2.2% and 3.9%, respectively, for type 2 diabetes in Nigeria. The annual increase was 0.3% in prevalence rate. A good number of people still live with it undiagnosed. The prevailing trend to replace the consumption of more complex forms of traditional diets with high intake of refined carbohydrates (Western) diets, in Nigeria, calls for great concern and urgent action. This is because carbohydrate (CHO) foods form over 70% of the local diets. The bleak account of national prevalence poses great challenges to individuals and the nation. Diabetes mellitus is a significant contribution to medical morbidity and mortality risk worldwide. Many factors are involved in its aetiology. The general risk factors include age, obesity, physical inactivity and family history/ previous history of gestational diabetes and poor eating habits. This is because intakes of good sources of dietary fibre such as fruits, vegetables, whole and high fibre grain products and legumes are low due to changes in dietary habit (nutrition transition) across the globe [58]. The main diabetes related risk factors include hyperglycaemia, hyperinsulinaemia/insulin resistance and microalbumi‐ nuria/proteinuria [59].
