Whole grains are defined as food products derived from cereal grains that retain their original bran, germ and endosperm levels. Refined grains have most of the bran and germ layers removed to leave just the starchy endosperm. As the bran and germ contain most of the micronutrients within the cereal grain, removal of these layer may negatively affect the quality of the food and as a result health may be affected. The typical Western diet is characterised by high levels of refined grains and this may explain the high prevalence of Western lifestyle diseases amongst the populations of Western countries. Evidence suggests that whole grain consumption is cardioprotective. A number of epidemiological studies have investigated the association between whole grain consumption and cardiovascular disease and shown that as whole grain intake increases, the risk of cardiovascular disease decreases. Put another way, as the consumption of refined grains increases, the risk of cardiovascular disease increases significantly.
Clinical studies have shown that whole grains show a number of health benefits that could explain their apparent cardioprotective effects including the ability to lower inflammation, their beneficial glycaemic effects and their ability to cause weight loss. However, it is not clear as to which of the mechanisms is responsible for the observed association. Researchers have investigated the associations between whole grains and particular health outcomes relating to cardiovascular disease. For example, in one study1, researchers used a health questionnaire to assess the dietary intake of whole grains in a large group of individuals. The researchers then calculated the association of the whole grain intake with biochemical parameters relating to cardiovascular disease. The results showed that whole grain intake was inversely related to homocysteine levels. Subjects in the highest quartile of whole grain intake had a 17 % lower plasma concentration of homocysteine compared to those in the lowest quartile of intake.
High levels of homocysteine are considered a risk factor for cardiovascular disease and elevated levels can be lowered by consumption of vitamin B6, B12 and folic acid. Whole grains are good sources of these B vitamins, with high concentrations being present in the bran and germ layers. Refined grains, absent the bran and germ layer are low in these vitamins. In addition, those in the highest quartile of whole grain intake also had a 14 % lower plasma insulin level and a 14 % lower plasma concentration of C-peptide (a peptide required for insulin production). High insulin levels are associated with the development of insulin resistance and the metabolic syndrome, both of which increase the risk of cardiovascular disease considerably. If whole grains lower insulin levels, this may be a significant cardioprotective effect. An inverse association between whole grain intake and high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol and total cholesterol were also observed.
Those subjects in the highest quartile for whole grain intake had a 14 % reduced plasma leptin concentration compared to those in the lowest quartile for leptin intake. The lower leptin levels seen in subject with higher whole grain intakes is interesting. Leptin levels rise with the degree of insulin resistance and as body weight increases. High leptin levels in the obese signify a degree of leptin resistance, and the inverse association between whole grain intake and leptin levels suggests that whole grains may decrease the risk of insulin resistance and weight gain. This contention is certainly supported by a considerable amount of data. Taken in their entirety, these results suggest that consumption of whole grain is associated with improvements in a number of biochemical parameters that explains the cardioprotective effects of whole grains. Avoiding refined grains and basing starch intake on whole foods is therefore likely to be an effective cardioprotective strategy.
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