Whole grains may be protective of cardiovascular disease, gastrointestinal ill health, cancer and diabetes. Evidence also suggests that diets high in whole grains reduce the weight gain seen with ageing. A number of epidemiological studies have suggested that whole grain consumption is inversely associated with weight gain and may be protective of obesity. Whole grains are defined as foods containing the same proportions of germ, endosperm and bran as in the original plant material. The outer bran section contains micronutrients, insoluble fibre as well as phytonutrients that may be important to health. The refining process tends to remove the bran part of the whole grain resulting in the loss of nutrients in the final product. Western diets tend to be high in refined grains that retain the starchy germ and endosperm but lack the high fibre nutrient dense bran component.
Science has investigated the association between whole grain consumption and long-term weight gain. For example, researchers1 used self-reporting questionnaires to assess the lifestyle and diets of 27 082 men aged between 40 and 75 years periodically over an 8 year period and then assessed their body weights at the end of this time. The results showed that the study participants tended to gain weight over the 8 year period and the mean weight gain was 1.9 kg. However, an increase in whole grain intake was inversely associated with weight gain, with every 40 g per day increase of whole grains being associated with a 0.49 kg reduction in weight gain. Supplementary bran that was added to the diet further reduced weight gain in a dose dependent manner such that for ever 20 g per day of bran, weight gain decreased by 0.36 kg.
Interestingly, dietary fibre was inversely associated with weight gain independent of whole grain consumption. For every 20 g per day increase in fibre there was a decrease in weight gain of 5.5 kg. Of this fibre content, the inverse association were observed for fruit and cereal fibre, but not vegetable fibre (with fruit fibre showing the strongest inverse association). For every 20 g per day increase in fruit and cereal fibre, weight gain was reduced by 2.51 kg and 0.81 kg, respectively. For fruit, apples accounted for most of the fibre content and the incorporation of a single apple into the diet decreased weight gain by 0.67 kg over the 8 year period. These findings are consistent with other studies and with recommendations to increase whole grain foods and total fibre content of the diet to prevent weight gain.
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