A growing percentage of the world's population is overnourished rather than undernourished and this is reflected as the term 'malnutrition' increasingly used also to express overnutrition (Darnton-Hill, Nishida and James, 2004). For populations undergoing urbanization, increases occur in the relative levels of nutrition over several generations (Reddy, 2002). Epidemiological work describes how such a pattern of nutrition facilitates subsequent catch-up growth, increased adult BMI and reduced lean body mass, all of which are important factors contributing to the risk of the metabolic syndrome (Sayer etal., 2004). For over 40 years it has been known that postnatal restriction of nutrition in animals enhanced longevity (Berg and Simms, 1960; McCay etal., 1975). Ozanne and Hales (2004) refined these findings, showing that control of the growth of male rats during suckling not only increased longevity but protected against the effects of an obesity-inducing diet later in life. Using a similar method Desai etal. (2005) found that modulating the pattern of catch-up growth could prevent the occurrence of obesity in later life. These findings concur with epidemiological observations previously discussed and shed light on observations that breastfeeding lowers the subsequent risk of obesity and possibly CVD in later life (Arenz etal., 2004; Rich-Edwards etal., 2004). The period of postnatal growth may be a critical time during which the pattern of nutrition can affect subsequent longevity.
Such strategies focus on the postnatal aspects of nutrition. The PARs concept also suggests that reducing maternal constraint during pregnancy could decrease the relative difference between pre- and postnatal levels of nutrition. Jackson (2000) suggests that maternal height, weight and body composition relate maternal metabolic reserve and capacity to optimize foetal nutrition, in other words, the level of maternal constraint. Several studies (e.g. the Southampton Women's Survey) are examining how maternal constraint affects pregnancy outcome by analysis of maternal characteristics, diet and lifestyle. A recent paper describes effects on the foetal distribution of umbilical venous blood flow to the ductus venosus and the foetal hepatic circulation. In women who were thinner and those eating relatively unbalanced diets there was a significant shift in foetal blood flow towards the liver and away from the ductus venosus (Haugen etal., 2005). Several trials are also currently underway to examine the effects of dietary supplementation in pregnancy.
In the USA today an increasing number of children are seen to have risk factors for CVD and are expected to develop the metabolic syndrome (Kohen-Avramoglu, Theriault and Adeli, 2003; Steinberger and Daniels, 2003). More than 60 per cent of overweight children have at least one additional risk factor for CVD, whereas 20 per cent have a further two (Dietz, 2001). The PARs concept suggests that chronic disease is more likely when the level of postnatal nutrition exceeds the level predicted by the prenatal environment. The experimental evidence discussed previously provides a physiological basis for the development of CVD under such circumstances. This runs parallel with the dietary transitions observed as rural economies in developing countries become industrialized. For those countries whose urbanization has already occurred, such as the USA and UK, the PARs concept suggests the level of postnatal nutrition may have already exceeded a level compatible with long-term health. A situation exacerbated by the relatively sedentary level of physical activity seen in industrialized countries. Such lifestyles may be beyond the capacity of the maternal-foetal unit to mount appropriate adaptive responses during pre- and early postnatal development. Studies such as the Southampton Women's Survey are attempting to answer this question.
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