A large number of studies have shown that a diet rich in vegetables may provide protection against many chronic diseases. We reviewed approximately 560 studies published since 1990, divided into four groups: 1) epidemiological studies on a high intake of vegetables, 2) human studies on vegetable ingredients, 3) animal studies on vegetable ingredients, and 4) physiological studies on each vegetable.
Many cohort and case-control studies have reported that a higher consumption of vegetables was inversely related to the risk of chronic diseases. This epidemiological evidence has shown the preventive effect on the incidence of cardiovascular disease and on all types of cancer, specifically of cancer of the lung, stomach and colon. This effect has been suggested to be attributable to the ingestion of micronutrients and numerous phytochemicals in vegetables. Some reports have shown the physiological effects on humans of specific ingredients such as carotenoids and flavonoids. Reports on the physiological effects of vegetable ingredients on experimental animals are increasing, the effects on the liver, cancer, immunization, and nervous and circulatory systems having been well investigated. Some vegetables have been reported to possess such physiological functions as anti-cancer, immune-enhancing and hypolipidemic effects.
It would appear that major public health benefits could be achieved by substantially increasing the consumption of vegetables. However, the some studies have also shown null and/or negative effects on health from an increased consumption of vegetables. It is therefore necessary to continue searching for scientific evidence about the role of vegetables.
