Fruit and vegetables contain a myriad of phytonutrients, some of which have been shown to provide health benefits to those who regularly consume them. High quantities of fruit and vegetables in the diet are associated with lower levels of chronic diseases such as cardiovascular disease and cancer in epidemiological studies. Plant foods are a good source of dietary fibre because they contain a number of soluble and insoluble fibres that make up structural components of the plant. In addition, plants contain vitamins, minerals, as well as polyphenols and carotenoids. One possible explanation for the beneficial effects of plant foods is that they contain high levels of antioxidant chemicals that prevent free radical damage to cells and tissues of the body. Another protective mechanisms might be the beneficial effects that folate has on homocysteine metabolism.
Research published in the Journal of Nutrition in 20001 investigated the effects of fruit and vegetable diets on plasma levels of antioxidants and homocysteine. Healthy male and female subjects were fed either a high or low fruit and vegetable diet for 4 weeks. The high diet consisted of 500 g of fruit and vegetables which contained 13.3 mg of total carotenoids, 172 mg of vitamin C and 228.1 µg of folate. The low diet consisted of 100 g of fruit and vegetables and contained 2.9 mg carotenoids, 65 mg vitamin C and 131.1 µg folate. After 4 weeks the subjects in the high diet had higher plasma levels of lutein (46 %), β-cryptoxanthin (128 %), lycopene (22 %), α-carotene (121 %), β-carotene (45 %), vitamin C (64 %) and folate (15 %). In addition, subjects on the high diet had plasma homocysteine levels that were 11 % lower.
The lower plasma levels of homocysteine seen in the subjects on the high diet is interesting because homocysteine is a risk factor for cardiovascular disease (here). This research demonstrates that one of the possible protective mechanisms of diets high in plant food might result from the high folate content of many fruits and vegetables. Spinach, broccoli, cauliflower, strawberries, lentils and blackberries all have reasonable high levels of folate. Research suggests there is an inverse relationship between homocysteine levels and cardiovascular disease. Previous research has shown that folate supplements are effective at lowering plasma homocysteine levels and the folate absorption from supplements is higher than that from fruit and vegetables. High levels of fruit and vegetables also raise plasma levels of important antioxidant compounds which may be an alternative mechanism by which they protect from chronic disease.
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