Whole fruit linked to reduced risk of diabetes, says study

Eating more whole fruits -- particularly blueberries, grapes and apples -- is associated with a lower risk of Type 2 diabetes, suggests new research from the Harvard School of Public Health.

The study, published Thursday in the British Medical Journal, reveals that people who had two servings of blueberries, grapes or apples per week reduced their risk of diabetes by as much as 23 per cent in comparison to those who ate less than one serving per month.

However, those who consumed one or more servings of fruit juice each day increased their risk of developing Type 2 diabetes by as much as 21 per cent. Swapping three servings of juice per week for whole fruits resulted in a 7 per cent reduction in risk of diabetes.

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“While fruits are recommended as a measure for diabetes prevention, previous studies have found mixed results for total fruit consumption," says senior author Dr. Qi Sun from Harvard University and Brigham and Women’s Hospital. "Our findings provide novel evidence suggesting that certain fruits may be especially beneficial for lowering diabetes risk.”

The researchers examined 187,382 participants from three long-term studies during 1984-2008. Food frequency questionnaires were used every four years to assess participants' habitual diet.

The study is the first to look at the effects of individual fruits on diabetes risk. People who ate three standard servings a week of blueberries had a 26 per cent lower risk of diabetes, while grapes and raisins stood at a 12 per cent reduction, and apples and pears cut the risk by 7 per cent. Prunes also had a protective effect, giving an 11 per cent reduction in risk. Other fruits such as bananas, plums, peaches and apricots had a negligible impact.

“Our data further endorses current recommendations on increasing whole fruits, but not fruit juice, as a measure for diabetes prevention,” says lead author Isao Muraki from Harvard University.

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The researchers theorize that the beneficial effects of certain individual fruits could be the result of a particular component, but more research is needed to determine which components. For example, previous studies have linked anthocyanins found in berries and grapes to lowered heart attack risk.

The relatively high glycemic index of fruit juice along with "reduced levels of beneficial nutrients through juicing processes" may explain why juice increases the risk of type 2 diabetes, the authors suggest. Juice passes through the digestive system more rapidly than fiber-rich fruit.

The study was funded in part by the National Institutes of Health and the National Heart, Lung and Blood Institute.