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NutrInsight • Whole grain and health: new evidence
2.4 Cancers
Jacobs et al. conducted a meta-analysis of forty observational studies (from the US, Italy, Central Europe) published between 1984 and 1997. The pooled odds ratio (0.69) for cancer risk compared between high intake vs. low intake of whole grain foods was a highly significant risk reduction [Jacobs et al., 1998], but additional published studies have not been evaluated further since that time. As would be expected from the body of evidence now available, the beneficial associations are strongest for cancers of the gastrointestinal tract. Two very recent studies in the USA have supported this conclusion. Schatzkin [Schatzkin et al., 2007; Schatzkin et al., 2008] showed that high whole grain consumers had lower risk of colorectal and intestinal cancer. However a study in Denmark has not shown a consistent effect of whole grain reducing risk of colon cancer in women, although it did in men, possibly due to the high baseline intake of whole grain in Denmark [Egeberg et al., 2010]. Lam et al. [Lam et al., 2010] used data on nearly half a million people from the NIH-AARP study to show that the risk of head and neck cancers was reduced with increased whole grain intake.
2.5 Body weight and fat distribution
Many cohort studies show reduced BMI with increasing whole grain intake. The decreased BMI range is between 0.5 and 1.7 kg/m2 comparing the highest whole grain consumers with the lowest whole grain consumers [Seal and Brownlee, 2010]. In addition, data from some prospective studies have also suggested that weight gain over time is lower in those who consume more whole grain [Bazzano et al., 2005].
Data from 15 studies were reviewed and subject to meta-analysis [Harland and Garton, 2008]. A modest reduction in BMI of 0.58 kg/m2 and a reduction in waist circumference of 2.7 cm was shown with consumption of three servings of whole grain per day. These changes are relatively small and their significance is difficult to evaluate. Interestingly, not all studies showed positive benefits of whole grains.
There are plausible reasons why body weight might be lower in those consuming whole grains. Whole grain foods have a higher fibre content and may also have a lower glycemic index with a larger particle size compared with refined grain flours. As a result they may have a slower digestion, increase satiation and satiety, and reduce postprandial metabolite and hormonal responses. These factors together may result in a cumulative reduction in overall energy intake.
Abdominal obesity is acknowledged to be a greater health risk than total obesity and so it is of interest that the association of whole grain cereal consumption with reduced amounts of visceral fat has recently been shown in Framingham Heart Study participants [McKeown et al., 2010]. Mechanisms linking whole grain intake with a beneficial fat distribution have yet to be proposed.
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