Whole grains may decrease diabetes risk

Background: High calcium intake has been linked to lower risk of diabetes in the past (1), though this association may have been confounded by magnesium intake (2). Likewise, high magnesium intake has also been linked to lower risk of diabetes (3).
Whole grains contain phytic acid which has been linked to decreased absorption of magnesium, calcium and other minerals from the gastrointestinal tract (4). The combination of these factors is sometimes used to prove that whole grains are to increase diabetes risk. However, the theory is very simplistic not taking into account other nutrients in whole grains and not taking into account the complexity of the human body.
If whole grains are to increase diabetes risk, then it would be expected that people with high intakes of whole grains have higher risk of diabetes than people with lower intakes. This association can be examined in human trials.

Methods: A group of scientists searched the scientific databases MEDLINE and EMBASE for prospective cohort studies examining whole grain intake in relation to risk of type 2 diabetes (5). Results from 6 cohorts could be included in the following meta-analysis. The studies included a total of 286,125 participants and 10,944 cases of diabetes type 2.

Table 1:

Results: Table 1 shows results from the 6 individual studies as well as the average (combined) effect. A 21% lower risk of diabetes was found for each 2 serving per day increment in intake of whole grains (RR = 0.79; 95% CI = 0.72-0.87). Table 1 also shows that a protective effect was found in all 6 cohorts. And that protective effects were significant in all cohorts, except for the cohort examined by Montonen et al.

Conclusion: Results from prospective cohort studies consistently show that subjects with higher whole grain consumption have lower risk of diabetes type 2.

References:
1) Pittas AG et al. The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis.J Clin Endocrinol Metab. 2007 Jun;92(6):2017-29.  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2085234/?tool=pubmed
2) Dong JY et al. Dietary calcium intake and risk of type 2 diabetes: possible confounding by magnesium. Eur J Clin Nutr. 2012 Feb 8. doi: 10.1038/ejcn.2012.5. http://www.ncbi.nlm.nih.gov/pubmed/22318650
3) Dong JY et al. Magnesium intake and risk of type 2 diabetes: meta-analysis of prospective cohort studies. Diabetes Care. 2011 Sep;34(9):2116-22. http://www.ncbi.nlm.nih.gov/pubmed/21868780
4) Zhou JR et al. Phytic acid in health and disease. Crit Rev Food Sci Nutr. 1995 Nov;35(6):495-508. http://www.ncbi.nlm.nih.gov/pubmed/8777015
5) de Munter JS et al. Whole grain, bran, and germ intake and risk of type 2 diabetes: a prospective cohort study and systematic review. PLoS Med. 2007 Aug;4(8):e261. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1952203/?tool=pubmed

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