Obesity is a Worldwide phenomenon that is reaching epidemic proportions. However, analysis of obesity data however shows that its prevalence tends to be associated with living in developed nations, such as Western Europe, North America and Australasia, and with consumption of a typical Western diet. The typical Western diet is hard to define as it contains a wide range of heterogenous foods. However, analysis of the typical Western diet has shown that it is characterised by high levels of refined and processed foods. In particular, the carbohydrate sources in the diet are stripped of their bran and germ layer during processing, and this removes fibre and micronutrients, leaving just the starchy endosperm. In addition, the processing of fruits and vegetables for example, produces products that are high in sugar but low in fibre and other nutrients. Evidence suggest that consumption of refined carbohydrates in the form of starch and sugars may be responsible for the development of a cluster of physiological changes that are termed the metabolic syndrome.
The metabolic syndrome is characterised by an insulin resistant state that is associated with detrimental changes to blood sugar and insulin homeostasis, as well as weight gain in the visceral adipose compartment. Epidemiology has shown that diets high in fruits and vegetables are protective of obesity, although the reason for this is unclear. However, it has been suggested that the protective effects of fruits and vegetables against obesity may relate to the soluble fibre and polyphenol content of plant foods, And beneficial effects on postprandial glycaemia and have been reported in those increasing fruit and vegetable intakes. In addition, the soluble fibre and polyphenols contained within fruits and vegetables may have insulin sensitising effects. Fruits tends to be right in the flavonoid group of polyphenols and contain the soluble fibre pectin. Vegetables are rich in fibre and some also contain substantial amounts of polyphenolic substances. As well as providing beneficial health effects, the consumption of greater concentrations of fruits and vegetables tends to lower intakes of refined and processed foods which may contain metabolic poisons.