Whole‐grain intake and cancer: An expanded review and meta‐analysis

Abstract

Whole grains are nutrient rich and may protect against chronic disease. To study this, we previously reviewed 14 case‐control studies of colorectal, gastric, and endometrial cancers and found consistently lower risk in those with high than in those with low whole‐grain intake. Questions remained concerning other cancers, dietary assessment, quantity consumed, confounding, and differential study quality. Here we expand the review to 40 case‐control studies of 20 cancers and colon polyps. Odds ratios are <1 for 46 of 51 mentions of whole‐grain intake and for 43 of 45 after exclusion of 6 mentions with design/reporting flaws or low intake. The pooled odds ratio for high vs. low whole‐grain intake among the 45 mentions was 0.66 (95% confidence interval = 0.60–0.72); they range from 0.59 to 0.78 across four types of dietary questionnaires. Odds ratios were <1 in 9 of 10 mentions of studies of colorectal cancers and polyps, 7 of 7 mentions of gastric and 6 of 6 mentions of other digestive tract cancers, 7 of 7 mentions of hormone‐related cancers, 4 of 4 mentions of pancreatic cancer, and 10 of 11 mentions of 8 other cancers. Most pooled odds ratios for specific cancers were in the range of 0.5–0.8, notable exceptions being breast (0.86) and prostate (0.90). The pooled odds ratio was similar in studies that adjusted for few and many covariates. Dose‐response associations were stronger in studies using food‐frequency questionnaires than in more quantitative questionnaires. The case‐control evidence is supportive of the hypothesis that whole‐grain intake protects against various cancers.