The new study, published in the journal Diabetes Care (Vol. 29, pp. 775-780), adds to a number of observational studies linking whole grains to lower risks of the disease - news that has already been grasped by cereal makers as the number of wholegrain products rises.
Sales of whole grains products in the US have increased following recommendations of the health benefits in the USDA's new Dietary Guidelines for Americans.
In Europe, the Healthgrain Integrated Project was recently launched to identify new sources of nutritionally enhanced grain, as well as to develop methods to make cereal products more appealing to consumers.
The controlled, single-blind, cross-over study, led by Martin Weickert from the German Institute of Human Nutrition, Potsdam, randomised 17 overweight or obese women, average age 53, with normal glucose metabolism, to eat nine macronutrient matched portions of fibre-enriched bread or control bread during a 72-hour period.
The fibre-enriched bread provided 31.2 grams of insoluble fibre per day, while the control bread was standard white bread.
"When analysing results for the entire cohort, intake of fibre-enriched bread for 72 hours significantly improved whole-body glucose disposal; this was equivalent to an eight per cent improvement of insulin sensitivity," reported Weickert.
The researchers reported no significant changes in plasma glucose, serum insulin, magnesium concentrations, blood lipids or serum insulin after eating the fibre-enriched bread, compared to control.
The molecular mechanism behind these improvements are not clear, say the researchers.
"Insoluble fibre, containing mainly cellulose and hemicellulose, are unlikely to be physiologically inert and may be interesting candidates for future research," they said.
One possible mechanism involving increased magnesium intake improve insulin sensitivity, as proposed by a recent study, but the magnesium content of both test and control breads were identical, and no increase in serum concentrations of magnesium were observed, suggesting this is not the mechanism responsible for the effects reported by Weickert and colleagues.
The authors point out that the use of fibre supplements has been criticised, but, seeing as many people are falling short of recommended levels, they say: "It seems important to identify active substances of dietary fibres that may have favourable health effects."
"An emphasis on cereal, fruit, and vegetable consumption containing a particularly high proportion of insoluble dietary fibre might be a safe, effective, and low-cost approach to reduce insulin resistance," they concluded.
An estimated 19 million people are affected by diabetes in the EU 25, equal to four per cent of the total population. This figure is projected to increase to 26 million by 2030.
In the US, there are over 20 million people with diabetes, equal to seven per cent of the population. The total costs are thought to be as much as $132 billion, according to 2002 American Diabetes Association figures.