Dietary phytochemicals

Glucosinolates have been shown to affect insect predation some act as feeding deterrents to certain species of insects but other insects such as the large white butterfly larvae are attracted by specific glucosinolates. There is also evidence that glucosinolates have antifungal and antibacterial activities and their presence in the plant may contribute to resistance to infection by mildew and other fungi. 

It is important to be aware of the sheer numbers of phytochemicals. Attention tends to be focused on a few representatives of each class but 25 000 members of the terpenes have been identified, as have many tens of thousands of polyphenols and there are even 250 different sterols although these do not all occur in foods or even traditional medicines. 

In the following sections each vegetable will be discussed briefly. Particular phytochemicals will be highlighted, but this should not be taken as an indication that these are the only phytochemicals associated with the foodstuff as it is evident that the phytochemical content of some dietary fruits and vegetables have been investigated in detail while others have received very little, if any, attention. 

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Ohnishi H, Asamoto M, Tujimura K, Hokaiwado N, Takahashi S, Ogawa K, et al. Inhibition of cell proliferation by nobiletin, a dietary phytochemical, associated with apoptosis and characteristic gene expression, but lack of effect on early rat hepatocarcinogenesis in vivo. Cancer Sci 2004 95 936-42. 

The mucosa of the GIT represents an interface between the external and internal environments. The expansive surface area is necessary for the efficient hydrolysis of foodstuffs and the absorption of energy and nutrients. The mucosa also influences the systemic availability of non-nutrient compounds in the diet, both beneficial and detrimental. Digestion and absorption of glucosinolates are critical determinants of health benefits (see Chapter 4) Similarly, the bioavailability and health benefits of phytoestrogens, such as genistein (see Chapters 5 and 10) are at least partly dependent on the carrier-mediated processes of absorption associated with the GIT (Oitate et al, 2001). Moreover, the metabolic activities of the mucosa can influence the systemic concentrations and forms of dietary phytochemicals, as exemplified by research with soy isoflavones (Andlauer et al., 2000). 

To define the beneficial (or adverse) effects of dietary phytochemicals research is required which can study effects at doses that reasonably reflect likely human exposures and which will ... 

Carter, O., Bailey, G.S., and Dashwood, R.H., The dietary phytochemical chlorophyllin alters E-cadherin and P-catenin expression in human colon cancer cells International Research Conference on Food, Nutrition and Cancer, J. Nutr., 134,3441S, 2004. 

Cooper, D.A. et al., Evaluation of the potential for olestra to affect the availability of dietary phytochemicals. J. Nutr, 127, 1699S, 1997. 

Mandlekar, S., J. L. Hong, and A. N. Kong. 2006. Modulation of metabolic enzymes by dietary phytochemicals a review of mechanisms underlying beneficial versus unfavorable effects. Curr Drug Metab 7(6) 661—675. 

The recent increase in consumer awareness on the health benefits of dietary phytochemicals accompanied by the rapid progress in the field of molecular biology have provided the means and incentive to enhance the functional value of plant material. This enhancement of health-promoting compounds is being tackled using a variety of approaches, which are discussed in the ensuing sections. 

Flavonoids are natural dietary phytochemicals and are currently the focus of much nutritional and therapeutic interest. However, the benefit of dietary flavonoids as part of a diet or as supplements is unclear. Results of population studies suggest that adopting flavonoid-rich diets may protect against cardiovascular disease [Hertog et al., 1995 Keli et al., 1996 Knekt et al., 1996 Huxley et al., 2003 Sesso et al., 1999 Yochum et al., 1999 Hirvonen et al., 2001 ... 

Surh Y-J. 2003. Cancer chemoprevention with dietary phytochemicals. Nature Rev Cancer 3 768-780. 

Manach, C. Hubert, J. Llorach, R. Scalbert, A. 2009. The complex links between dietary phytochemicals and human health deciphered by metabolomics. Mol. Nutr. Food Res. 53 1303-1315. 

Vattem DA, Mihahk K, Crixell SH, McLean RJ. Dietary phytochemicals as quorum sensing inhibitors. Eitoterapia 2007 78 302— 310. 

Barnes, S. Sfakianos, J. Coward, L. Kirk, M. Soy isofla-vonoids and cancer prevention underlying biochemical and pharmacological issues. Adv. Exp. Med. Biol. 1996, 401, 87-100 (Special Issue Dietary Phytochemicals in Cancer Prevention and Treatment). 

Surh, Y.J. (2003) Cancerchemoprevention with dietary phytochemicals. Nature Reviews. Cancer, 3 (10), 768—780. 

IpC,LiskDJ. 1996. The attributes of selenium-enriched garlic in cancer prevention. In American Institute for Cancer Research, eds. Dietary phytochemicals in cancer prevention and treatment. New York, NY Plenum Press, 179-187. 

Kohle, C. and Bock, K. W. (2006) Activation of coupled Ah receptor and Nrf2 gene batteries by dietary phytochemicals in relation to chemoprevention. Biochem. Pharmacol. 72, 795-805. 

Figure 1 General scheme for uptake and pharmacokinetics of dietary phytochemicals.

Against this background it is to be expected that much detailed information on phytochemical metabolism and absorption will emerge over the next decade and will provide a firm basis for industrial exploitation of dietary phytochemicals and societal health benefit. 

There are several reports on ITCs and flavonoids acting as chemopreventive agents against HCA-induced DNA adduct formation and carcinogenesis in rats [4, 9, 95]. Dietary phytochemicals can inhibit phase i activation and induce phase 11 detoxification enzymes and, therefore, attenuate the effect of PhiP on DNA adduct formation. ITCs, such as BITC, and quercetin strongly inhibit PhiP A-hydroxylation in rat liver microsomes and protect against PhIP-DNA adduct formation in rat colon [9, 14]. 

The ultimate goal is to understand the relationship between HCAs and human cancer and to search for various measures to reduce the risk of, or to prevent, cancer. Food contains a complex mixture of nutrients, vitamins, additives, contaminants, and phytochemicals. The simplest way to reduce risk is to reduce the intakes of HCAs where possible through modified methods of cooking and, at the same time, to encourage the consumption of fruits and vegetables, especially of the cruciferous family. The results presented here support the epidemiological evidence that dietary phytochemicals can protect against cancer [108, 109],... 

The beginning chapters of this volume are devoted to aspects of phytochemical research that are fundamental to this new era of activity. Chapter 1 introduces the fundamentals of nutritional genomics (nutrigenomics), notably DNA arrays, proteomics, and metabolomics, while Chapter 2 indicates the manifold factors affecting bioavailability, critically compares various methods for its measurement, and highlights crucial differences between studies on new drug formulations and dietary phytochemicals. The fundamental importance of considering metabolic processes is addressed in Chapter 3, with particular attention to those associated with the ubiquitous polyphenols. 

Chapter 12 summarizes the role of dietary phytochemicals, especially those from fruits, herbs, and spices, in the prevention of cardiovascular disease. Chapter 13 is devoted to the effects and mecharusms of action of resveratrol, a polyphenolic phytoalexin that has received considerable publicity. The same is tine of lycopene, the topic of Chapter 14, which occurs in especially high levels in fresh and processed tomatoes. Consideration is given in Chapter 15 to the effects of oltipraz on phase 1 and 2 xenobiotic-metabolizing enzymes this draws together nutritional, clinical, and pharmacological investigation and provides some pointers for the future. These are elaborated upon in Chapter 16, which addresses research directions, challenges, and opportunities. 

Surh, Y.-J., Cancer chemoprevention by dietary phytochemicals, Nature Rev. Cancer, 3, 768,... 

Barnes, S. et al.. Soy isoflavonoids and cancer prevention Underlying biochemical and pharmacological issues, in Dietary Phytochemicals and Cancer Prevention, Butrum, R., Ed., Plenum Press, New York, 1996, 87. 

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