There have been a number of reviews of the relationship between wholegrain cereal consumption and cancer risk which all conclude that wholegrain foods are associated with lower cancer risk. In one review of 40 case-control studies of 20 cancers, the pooled odds ratio for high versus low wholegrain intake was 0.66 (95%CI: 0.60-0.72).

The evidence suggests wholegrain cereal foods and cereal fibre rich foods may protect against colorectal cancers, gastric cancers and possibly also breast, endometrial and prostate cancers. The consistency of evidence was recognised by the US FDA in July 1999 when a wholegrain health claim was approved. It permitted any low-fat product that contained 51% wholegrains by weight to claim “Diets rich in wholegrain foods and other plant foods and low in total fat, saturated fat, and cholesterol may reduce the risk of heart disease and some cancers.”

Regular consumption of wholegrain foods has been linked to a variety of positive health outcomes with respect to specific cancers:

Colorectal cancer:

• In case-control and cohort studies wholegrains have been shown to reduce the risk of developing cancer of the colon by as much as 30% and a meta-analysis of 11 cohort studies estimated a risk reduction of 6% for the development of colorectal cancer comparing the highest with lowest quintiles of wholegrain consumption. A meta-analysis of the largest two intervention studies with wheat bran concluded that there was a significant 19% reduction in risk of recurrence of adenomas in men, but not in women.

Gastrointestinal cancers:

• One prospective cohort study in 10 European countries with 312 incident gastric cancers found that intake of cereal fibre was protective (with a hazard ratio of 0.69 in the highest quartile). This is consistent with Italian case-control studies which estimate an odds ratio of 0.5 for risk of stomach cancer with the highest wholegrain intake.
• In a prospective cohort study of more than 400,000 people, intake of wholegrain foods and fibre from grains was inversely associated with risk of cancer of the small intestine, with an odds ratio of 0.59 in those with the highest quintile of wholegrain intake.

Respiratory tract cancers:

• The risk of cancers of the upper respiratory tract was reduced by 47% in the highest tertile of wholegrain consumption in the Iowa Women’s Health cohort study and similar protective effects have been reported in European populations as well.

Pancreatic cancer:

• People consuming more than two serves of wholegrains a day had a 40% lower pancreatic cancer risk in a large case-control study in California.

Breast cancer:

• Some case-control studies have reported significant protection against breast cancer with high fibre intakes.
• Rodent studies with chemically-induced mammary cancer have shown a significant protective effect of wheat bran when provided at 12% to 15% of fibre by weight against a high fat (40% of energy) diet. Wheat bran was shown to be capable of inhibiting mammary cancer in a way not shared by alpha-cellulose.
• A small Finnish cross-sectional pilot study investigated the association between whole rye and whole wheat consumption and risk of breast cancer. Alkylresorcinols, phenolic compounds found in rye and wheat bran, have been shown to be valid biomarkers of whole rye and whole wheat consumption. Rye and wheat fiber intake, as well as blood and urine levels of alkylresorcinol metabolites, all were found to be significantly lower in the breast cancer survivors compared to the vegetarian and non-vegetarian groups.

Endometrial cancer:

• An association between wholegrain intake and incident endometrial cancer was investigated as part of the Iowa Women’s Healthy Study, which included 23,014 women, aged 55-69 years in 1986. An inverse association between wholegrain intake and endometrial cancer was observed among never-users of hormone replacement therapy (p for trend = 0.05). There was no association between refined grain intake and endometrial cancer.

Prostrate cancer:

• Rye wholegrain and bran intake has shown beneficial effects on prostate cancer progression in animal models, including lower tumor take rates, smaller tumor volumes and reduced prostate specific antigen (PSA) concentrations. In a randomised controlled, crossover study with 17 men diagnosed with prostrate cancer, the effect of high intake of rye wholegrain and bran on prostate cancer progression, as assessed by PSA concentration, was investigated. Wholegrain and bran from rye resulted in significantly lower plasma PSA compared with a cellulose-supplemented refined wheat diet in patients with prostate cancer.

Suggested Mechanisms:

The mechanisms by which wholegrain foods may be cancer protective are not yet clear. A large prospective European study found that total dietary fibre was protective against colorectal cancer. Another cohort study concluded that it was not, but that wholegrain consumption lowered risk, suggesting that wholegrain components other than fibre may have a role to play.

The protective components could include fermentable carbohydrates, oligosaccharides, flavonoids, henolics, phytoestrogens, lignans, protease inhibitors, saponins and selenium. Protease inhibitors in grains (such as phytic acid, phenolics, and saponins) have been shown to reduce the risk of colon and breast cancer in animals, and in grains they make up 5-10% of the water-soluble protein, so they may be one possible mechanism. Chan et al (2007) suggested that another plausible biological mechanism for the reduction in cancer risk could be the decreased levels of insulin and/or inflammation observed with consumption of wholegrain foods.

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