Vegetables are those herbaceous plants whose part or parts are eating as supporting food or can serve as the main foods. They may be aromatic, bitter or tasteless (Edema, 1987).
Leafy vegetables also called potherbs, green vegetables or salad green are plants leaves eaten as vegetables sometimes they are accompanied by tender petioles and shoots.
Nigeria is endowed with a variety of additional vegetables and different types are consumed by the various ethnic groups for different purposes.
Pharmacological importance of leafy vegetables deals with the phytochemical component of a vegetable which determines its colour and medicinal effect (Phytochemical Aspect) and the nutritional importance of leafy vegetables deals with the nutrients present in the leafy vegetables consumed such as protein content, carbohydrate content, vitamin content etc.
Vegetables are eaten in a variety of ways as part of the main meal or as snacks. The nutrient content of leafy vegetables varies considerably, though generally they contain protein or fat and varies in the proportion of vitamin they contain such as vitamin A, vitamin K, and vitamin B, minerals and carbohydrate. Leafy vegetables are not major sources of carbohydrate compared with starchy food.
Several study have shown that adequate intake of these vegetables form an important part of a healthy diet and low fruit and vegetable intake constitute a risk factor for chronic diseases such as cancer, coronary heart disease, stroke and cataract formation (Van Duyn and Pivonka, 2000). Scientific evidence has shown that frequent consumption of vegetables can prevent esophageal, stomach, pancreatic, bladder and cervical cancer and that a diet high in vegetables could prevent 20% of most types of cancer (Crawford et al., 1994).
According to reports, vegetables consumption is influenced by gender, age income education and family origin ad as well as health status (Wadle et al., 2000, Giskes et al., 2002). Some vegetables are also reserves for the sick and convalescence because of their medicinal properties. In Nigeria, most rural dwellers rely on leaves gathered from the wild as their main source of leafy vegetables. These vegetables are harvested at all stages of growth and fed either as processed, semi-processed or fresh to man while they are usually offered fresh to live stock. Leafy vegetables are known to add taste and flavor, as well as substantial amount of protein fiber, minerals and vitamins to our diet (Oyenuga and Fetuga, 1975, Adewunmi, 1987). While the amount of nutrient constituent in the more commonly used leafy vegetables species in Nigeria have been studied to some extent (Kola, 2004), the lesser known region and local species remain virtually neglected. Lack of information on the specific nutrients and phytochemicals in a large number of the native vegetable species with which Nigeria is richly endowed is partly responsible for their under exploitation especially in areas beyond the traditional location where they are found and consumed.
This work covers the phytochemical and nutritional importance of some common leafy vegetables that are consumed in Nigeria. It intends to bring more to our notice the benefits of including these vegetables in our diets.