May 18, 2017
Whole grains are unrefined grains that haven't had their bran and germ removed by milling. For example: barley, brown rice, buckwheat, bulgur (cracked wheat), millet, oatmeal, popcorn, whole-wheat bread/pasta/crackers, and wild rice.
Conversely, refined grains include white flour, white rice, white bread and degermed corn flour.
Suspected Mechanisms of Action
Whole grains are rich in fibre, which can reduce the postprandial (after-meal) glucose and insulin responses leading to better glycaemic control.
Higher whole grain intake has been associated with a lower prevalence or risk of hypertension or raised blood pressure, hypertriglyceridaemia, and lower concentrations of total and low density lipoprotein cholesterol, which are important cardiovascular risk factors.
Whole grain intake has been associated with lower levels of inflammatory markers.
The following is a short collection of summaries of some major studies which have documented the effects of whole grain consumption.
100,000 participants returned surveys for 26 years
After adjustment for known risk factors, participants in the highest fifth of estimated gluten intake had a hazard ratio for coronary heart disease of 0.95
After additional adjustment for intake of whole grains (leaving the remaining variance of gluten corresponding to refined grains), the multivariate hazard ratio was 1.00
After additional adjustment for intake of refined grains (leaving the variance of gluten intake correlating with whole grain intake), estimated gluten consumption was associated with a lower risk of coronary heart disease (multivariate hazard ratio 0.85, 0.77 to 0.93
The avoidance of gluten may result in reduced consumption of beneficial whole grains, which may affect cardiovascular risk. The promotion of gluten-free diets among people without celiac disease should not be encouraged.
Meta-analysis of 45 studies
90 g/day increase in whole grain intake (90 g is equivalent to three servings—for example, two slices of bread and one bowl of cereal
There were reductions of 21%, 16%, 11%, and 18%, respectively, in the relative risk of coronary heart disease, cardiovascular disease, total cancer, and all cause mortality for the highest versus lowest category of whole grain intake.
There were also reductions of 19%, 36%, 20%, and 21% in the relative risk of mortality from respiratory disease, diabetes, infectious disease, and all non-cardiovascular, non-cancer causes, respectively, with a high versus low intake of whole grains.
Reductions in risk were observed up to an intake of 210-225 g/day (seven to seven and a half servings per day)
There was little evidence of an association with refined grains, white rice, total rice, or total grains
Substituting whole grains for refined grains in a 6-wk randomized trial
81 participants: healthy men and postmenopausal women
One group ate 200 g whole grains and one group only ate refined grains. body weight was maintained in both groups.
Results were not statistically significant but the refined grain group lost slightly more weight, gained slightly more lean mass, and had a few percent higher metabolic rate than the whole grain group
Whole grain intake and cardiovascular disease
Meta-analysis of seven studies
Greater whole grain intake (2.5 servings/d vs. 0.2 servings/d) was associated with a 21% lower risk of CVD events
Conversely, refined grain intake was not associated with incident CVD events
Women with the highest quintile for whole-grain intake had a reduction in CHD by 14 % (P=0·005) compared with the lowest quintile.
Women with the highest level of refined-grain intake had a 9 % increase in CHD risk (P=0·7) compared with women with the lowest level.
Women with the highest level of refined-grain intake had ischemic strokes at the same rate as women with the lowest intake.
Studies seem to indicate that whole grain consumption is marginally favourable to refined grain consumption and also marginally favourable to no grain consumption at all.