Why whole grains are protective: biological mechanisms

Abstract

Epidemiological studies find that whole-grain intake is protective against cancer, cardiovascular disease, diabetes and obesity. Potential mechanisms for this protection are diverse since whole grains are rich in nutrients and phytochemicals. First, whole grains are concentrated sources of dietary fibre, resistant starch and oligosaccharides, carbohydrates that escape digestion in the small intestine and are fermented in the gut, producing short-chain fatty acids (SCFA). SCFA lower colonic pH, serve as an energy source for the colonocytes and may alter blood lipids. These improvements in the gut environment may provide immune protection beyond the gut. Second, whole grains are rich in antioxidants, including trace minerals and phenolic compounds, and these compounds have been linked to disease prevention. Additionally, whole grains mediate insulin and glucose responses. Although lower glycaemic load and glycaemic index have been linked to diabetes and obesity, risk of cancers such as colon and breast cancer have also been linked to high intake of readily-available carbohydrate. Finally, whole grains contain many other compounds that may protect against chronic disease. These compunds include phytate, phyto-oestrogens such as lignan, plant stanols and sterols, and vitamins and minerals. As a consequence of the traditional models of conducting nutrition studies on isolated nutrients, few studies exist on the biological effects of increased whole-grain intake. The few whole-grain feeding studies that are available show improvements in biomarkers with whole-grain consumption, such as weight loss, blood lipid improvement and antioxidant protection.

The HEALTHGRAIN Cereal Diversity Screen: Concept, Results, and Prospects

“…Wholegrains are a good source of dietary fiber, vitamins, minerals, and phytochemicals, which have been suggested to contribute to their protective effects as compared to refined grains (5). The grain fiber as a single component has also been associated with significant risk reduction.…”

Influence of habitual diet on antioxidant status: a study in a population of vegetarians and omnivores

“…This has led to some researchers questioning the efficacy of antioxidants per se in reducing chronic disease risk and suggesting that antioxidants could merely be acting as a marker of the body status of 'other' entities, which might ultimately be responsible for the associations observed in epidemiological studies. At the same time, increased intakes of foods, also rich in antioxidants such as fruits and vegetables (Ness and Powles, 1997;Law and Morris, 1998;Genkinger et al, 2004;La Vecchia, 2004), and whole grain cereals (Slavin, 2003;Seal, 2006) have been associated with a decrease in the risk of chronic diseases including cancer and cardiovascular diseases.…”

Rice consumption, incidence of chronic diseases and risk of mortality: meta-analysis of cohort studies

“…Furthermore, high rice consumption is associated with high concentrations of inflammatory markers including plasminogen activator inhibitor type 1, C-reactive protein and fibrinogen (39) , which might mediate the risk for chronic diseases. In addition, due to the milling process, white rice has low content of many nutrients including insoluble fibre, magnesium, vitamins, lignans, plant stanols and sterols, and phyto-oestrogens (40) . Most of these nutrients have been associated with lower risk of chronic diseases in prospective cohort studies (40)(41)(42) .…”