Dr Alan Barclay
Getting to the heart of the wholegrain matter
Eating more wholegrain foods is associated with a lower risk of developing cardiovascular disease (heart disease and stroke) based on the evidence from a number of large observational studies published in recent years. For example, the Nurses’ Health Study reported that women who ate the most (an average of 2.5 servings a day) intact grain foods – generally wholegrain breakfast cereals, brown rice and whole grain bread – were 30% less likely to develop heart disease than women eating merely a single serving of these foods a week. Since then, ‘consume more wholegrains’ has become something of a mantra by dietitians, nutritionists and medical doctors, and is enshrined in dietary guidelines around the globe. But do all wholegrains reduce the risk of cardiovascular disease?
For oats and barley, there’s both observational and intervention (clinical trial) data suggesting that bran and some soluble fibre components in these grains improve blood cholesterol and other markers of cardiovascular disease risk. The picture is not so clear, however, when it comes to mixed sources of wholegrain foods, with conflicting results from the small number of clinical trials that have been published to-date.
In the most recently published clinical trial, researchers from the University of Newcastle upon Tyne have found that when they provided overweight but otherwise healthy men and women with a range of wholegrain foods and asked them to substitute them ‘like for like’ for refined grain foods in their typical diet over a 16 week period, there were no significant differences in any markers of cardiovascular disease risk (cholesterol, triglycerides, insulin sensitivity and a range of common inflammatory markers) between those who substituted wholegrain foods into their diet, and those who didn’t (the control group).
Writing in the British Journal of Nutrition the authors conclude: “… the duration of this controlled intervention study represents a very short period of dietary change in the context of lifelong dietary exposures, and may be insufficient to change the lifetime disease trajectory for these individuals with a strong pre-existing risk factor .... The present study sounds a note of caution to the specific health claims for whole grain-rich foods and cardiovascular health. However, it does not undermine more general efforts to promote whole grains as part of a healthy diet for the general population across the life course, based on data from observational studies.”
We don't know the full details about what the participants in this study ate, but using the data for the cereal grain foods that they were provided with (they are listed in Table 1 in the study), we cheekily estimated the (weighted) average GI of the wholegrains consumed in the diets – the men's would have been around 61 and the women's around 62. In fact, only one of the wholegrain foods given to the study participants – whole wheat pasta – was likely to have a low GI (≤ 55). As we said earlier in this issue (Can You Put a Number on a Low GI Diet?), it's an average GI of 45 that has been proven to have significant health benefits in people with existing diabetes and in reducing the risk of chronic diseases like heart disease and diabetes. At this stage, it appears unlikely that high GI wholegrains will have the same benefits.
Of course, that does not mean you should give up on wholegrains, they offer a range of other health benefits. Just say no thanks to finely milled grain foods even when they claim to be 'wholegrain' and head for the low GI, whole kernel grains, like those found in hulled or pearl barley, whole kernel wheat, grainy, granary breads like Burgen or Tip Top 9 grain bread, whole wheat pasta, and traditional porridge oats and mueslis like Morning Sun. If in doubt, look for the GI Symbol.
For more information about the GI Symbol Program
Dr Alan W Barclay, PhD
Chief Scientific Officer
Glycemic Index Foundation (Ltd)
Phone: +61 (0)2 9785 1037
Mob: +61 (0)416 111 046
Fax: +61 (0)2 9785 1037
1 May 2010
Posted by GI Group at 1:04 am