Vegetables phytochemicals

The discovery that, in industrialised societies, diets deficient in fruits and vegetables can effectively double the risk of developing many different types of cancer has focused renewed attention on the beneficial properties of these foods (Block e/a/., 1992 Patterson ef a/., 1990 Southon and Faulks, 2002). As we have seen, plant foods are rich in micronutrients, but they also contain an immense variety of biologically active secondary metabolites providing colour, flavour and natural toxicity to pests and sometimes humans (Johnson et ah, 1994). The chemistry and classification of such substances is still a matter for much research and debate, but this has not prevented attempts to isolate and exploit substances that have variously been termed protective factors , phytoprotectants , phytochemicals and nutraceuticals . Phytochemical compounds include ... 

The antioxidant activities of carotenoids and other phytochemicals in the human body can be measured, or at least estimated, by a variety of techniques, in vitro, in vivo or ex vivo (Krinsky, 2001). Many studies describe the use of ex vivo methods to measure the oxidisability of low-density lipoprotein (LDL) particles after dietary intervention with carotene-rich foods. However, the difficulty with this approach is that complex plant foods usually also contain other carotenoids, ascorbate, flavonoids, and other compounds that have antioxidant activity, and it is difficult to attribute the results to any particular class of compounds. One study, in which subjects were given additional fruits and vegetables, demonstrated an increase in the resistance of LDL to oxidation (Hininger et al., 1997), but two other showed no effect (Chopra et al, 1996 van het Hof et al., 1999). These differing outcomes may have been due to systematic differences in the experimental protocols or in the populations studied (Krinsky, 2001), but the results do indicate the complexity of the problem, and the hazards of generalising too readily about the putative benefits of dietary antioxidants. 

Since fruit and vegetable consumption is recommended as part of a healthy lifestyle, it could be argued that there is no need to obtain detailed safety data on individual phytochemicals that are present in these items of the diet. This ignores the fact that ... 

Furthermore, several studies have shown that in some individuals an increased intake of xanthophylls does not lead to increased levels of xanthophylls in their plasmas and/or retinas, and macular pigment densities do not exhibit a positive correlation with plasma levels of lutein and zeaxanthin (Aleman et al., 2001 Bernstein et al., 2002b Bone et al., 2000, 2001, 2003 Hammond et al., 1995,1997). These apparently conflicting epidemiological results need to be interpreted with caution as a diet rich in fruit and vegetables includes a great variety of phytochemicals that may independently, or in cooperation with lutein or zeaxanthin, and other dietary components affect carotenoid uptake and function in the retina. 

Extensive research in the last few years has revealed that the regular consumption of certain fruits containing carotenoids, an important group of phytochemicals derived from such fruits and vegetables, is involved in cancer prevention. Both prospective and retrospective epidemiological studies have consistently and clearly shown that an increased intake of fruits and vegetables rich in carotenoids is associated with a decreased risk of cancer (Mayne, 1996 Peto... 

Because of the great diversity of phytochemicals in fruits, vegetables, herbs and spices, only the major structural classes in the most common food plants, have been selected for discussion (see below and Figs. 15.2 and 15.3, for example, phytochemicals). These are also the phytochemicals for which there is generally the greatest information on food composition and health effects. 

The use of nitrogen fertilization results in higher content of N-containing compounds, including free amino acids, and also increases in terpene content in wood plants, whilst starch, total carbohydrates, phenylpropanoids and total carbon-based phytochemicals decreased (Koricheva et al., 1998). Higher levels of nitrogen favoured its uptake and increased the nitrate content of the crop, which is critical for salad vegetables and baby foods. 

Fruits and vegetables have historically been considered rich sources of some essential dietary micronutrients and fibers, and more recently they have been recognized as important sources for a wide array of phytochemicals that individually, or in combination, may benefit health (Stavric 1994 Rechkemmer 2001). Therefore, some people have conferred on fruits and vegetables the status of functional foods. There are many biologically plausible reasons for this potentially protective association, including the fact that many of the phytochemicals act as antioxidants. 

Phytochemicals present in fruits and vegetables are very diverse, such as ascorbic acid, carotenoids, and phenolic compounds (Liu 2004 Percival and others 2006 Syngletary and others 2005 Yahia and others 2001a, 2001b). Plant polyphenols are ubiquitous in the diet, with rich sources being tea, wine, fruits, and vegetables they demonstrate considerable antioxidative activity in vitro, which can have important implications for health (Duthie and others 2000). 

The consumption of a mixture of phenolic compounds presented in apple or purple grape juice inhibited mammary carcinogenesis in 7,12-dimethylbenzo[a]anthracene (DMBA) treated rats (Liu and others 2005 Jung and others 2006). However, the individual antioxidants of these foods studied in clinical trials, including (3-carotene, vitamin C, and vitamin E, do not appear to have consistent preventive effects comparable to the observed health benefits of diets rich in fruits and vegetables, suggesting that natural phytochemicals in fresh fruits and vegetables could be more effective than a dietary supplement. 

Lin and others (2003) indicated that high potassium, magnesium, and calcium content in addition to antioxidants, phytochemicals, and lower acidity of fruits and vegetables could be important factors for bone health. 

Fruits and vegetables are rich sources of phytochemicals, in addition to other components that may act synergistically with phytochemicals to contribute to the nutritional and health benefits of these food commodities. 

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