US researchers found that people who every day eat several servings of whole grains and limit intake of refined grains have less visceral adipose tissue or VAT, a type of body fat believed to trigger cardiovascular disease and type 2 diabetes.
You can read about the study by lead author Dr Nicola M McKeown and colleagues in the November issue of American Journal of Clinical Nutrition, which was made available online at the end of September.
McKeown is a scientist with the Nutritional Epidemiology Program at the US Department of Agriculture Human Nutrition Researcher Center on Aging (USDA HNRCA) at Tufts University in Boston, Massachusetts.
She and her co-researchers examined diet questionnaires completed by over 2,800 men and women aged from 32 to 83 who participanted in the Framingham Heart Offspring and Third Generation study cohorts as part of the Framingham Heart Study of the National Heart Lung and Blood Institute (NHLBI).
They also had the results of multidetector-computed tomography (MDCT) scans on the participants, from which they could work out volumes of VAT and subcutaneous adipose tissue (SAT).
SAT is situated just below the skin, while VAT surrounds the organs in the abdomen.
The researchers found VAT was about 10 per cent lower in the men and women who reported eating three or more servings of whole grains every day while limiting their daily intake of refined grains to less than one serving:
“For example,” said McKeown, who is also an assistant professor at the Friedman School, “a slice of 100% whole wheat bread or a half cup of oatmeal constituted one serving of whole grains and a slice of white bread or a half cup of white rice represented a serving of refined grains.”
Co-author Dr Paul Jacques, director of the Nutritional Epidemiology Program at the USDA HNRCA and a professor at the Friedman School of Nutrition Science and Policy at Tufts, said that previous studies had already suggested that VAT was linked to metabolic syndrome, a cluster of risk factors like high blood pressure, unhealthy cholesterol levels and insulin resistance, that can develop into cardiovascular disease or type 2 diabetes.
He said they were not surprised when they compared the relationship between VAT and SAT and whole and refined grain and found a “more striking association with visceral fat”.
“The association persisted after we accounted for other lifestyle factors such as smoking, alcohol intake, fruit and vegetable intake, percentage of calories from fat and physical activity,” he explained.
The researchers also noticed that men and women who ate on average three daily servings of whole grains but did not limit their intake of refined grains, did not have lower VAT volumes.
“Whole grain consumption did not appear to improve VAT volume if refined grain intake exceeded four or more servings per day,” said McKeown.
She explained that their results suggest it is important to substitute a less healthy food with a healthier one, rather than just add the healthy one to one’s diet.
“For example, choosing to cook with brown rice instead of white or making a sandwich with whole grain bread instead of white bread,” she added.
The researchers said while their study adds to other research that shows a link between higher whole grain intake and reduced risk of metabolic syndrome and insulin resistance, it is, like the others, an observational study, and the numbers are not that high, so really what needs to happen now is more robust, larger studies that specifically investigate whole grain consumption and body fat distribution, in much larger and diverse populations, in order to discover what drives the link.
Funds from the National Heart Lung and Blood Institute (NHLBI), the USDA, and the General Mills Bell Institute of Health and Nutrition helped pay for the study.
“Whole- and refined-grain intakes are differentially associated with abdominal visceral and subcutaneous adiposity in healthy adults: the Framingham Heart Study.”
Nicola M McKeown, Lisa M Troy, Paul F Jacques, Udo Hoffmann, Christopher J O’Donnell and Caroline S Fox.
American Journal of Clinical Nutrition Vol. 92, No. 5, 1165-1171, November 2010.
First published online on 29 September 2010; doi:10.3945/ajcn.2009.29106
Source: Tufts University.
Written by: Catharine Paddock, PhD