CHAPTER ONE
1.0
INTRODUCTION
Toward the end of the
20th century, epidemiological studies and associated meta-analyses suggested
strongly that long-term consumption of diets rich in plant foods offered some protection
against chronic diseases, especially cancer (Wallstromet al., 2000).Because uncontrolled production of free radicals was
thought to be significantly implicated in the etiology of cancer (Guyton and
Kensler 1993),these observations focused attention on the possible role of
radical scavenging and radical suppressing nutrients and non-nutrients in
explaining the apparent benefit of such diets (Weisburger, 1991).
The realization that free radicals were similarly implicated in the
etiology of many other chronic diseases (Kehrer, 1993 and Stohs, 1995), immediately focused
attention on flavonoids and the foods and beverages rich therein. An
unfortunate, but unintended side effect of some research works and papers was
the misleading tendency of many investigators to think of dietary phenols,
polyphenols, and tannins (PPT)as encompassing only the flavonoids, flavonols,
and flavones. More recent epidemiological studies have supported the
association between better health and long-term consumption of diets rich in
foods of plant origin(Hung et al.,
2004 and Jansen et al., 2004).However,
whether this is because such diets minimize exposure to deleterious substances
(example oxidized cholesterol, pyrolysis mutagens, salt, saturated fat, etc.),
or maximize intake of certain beneficial nutrients (example isothiocyanates and
other sulfur-containing plant constituents, mono-unsaturated fatty
acids, and poly-unsaturated fatty acids, PPT, polyacetylenes,
selenium, terpenes, etc.) or some combination as advocated in the ‘‘Polymeal’’
concept, remains unknown (Franco et al.,
2004 and Johnson, 2004).An in vitro study indicates that
there may be mechanistic basis for true synergy between PPT and isothiocyanates.
In contrast, more recent studies seeking to assess the suggested link between
the consumption of flavonols and flavones, or other flavonoids, have given much
less consistent results. Some studies have suggested a possible protective
effect of flavonoids against vascular diseases (Hirvonen et al., 2001 and Mennen et al.,
2004) or certain (but not all) cancers(Knekt et al., 1997 and Sun et al.,
2002).Interestingly, an investigation of the relationship between the
consumption of Hibiscus sabdariffa
(zobo) and other cruciferous vegetables and the risk of breast cancer in
premenopausal women has to be carried out in order to ascertain the beneficial
effects to isothiocyanates and/or the phenolic components of the plants (like
the dietary phenols including flavonoids) in the management of cancer growth
and initiation of various types of diabetes.
In the same time period, various studies have suggested beneficial
effect associated with raised consumption of other classes of dietary phenols.
For example, increased coffee consumption has been linked with reduced
incidence of type II diabetes (van Dam et
al., 2002 and Saremi et al.,
2003).Similarly, increased consumption of lignans (or at least greater plasma
concentrations of their metabolites)has been linked with reduced incidence of
estrogen-related cancers in some (Boccardo et
al., 2004 and McCann et al.,
2004) but not all studies (Kilkkinen et
al., 2004 and Zeleniuch –Jacquotte et
al., 2004),and a prospective study was equivocal.
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