Eating more whole fruits, particularly blueberries, grapes, and apples, was significantly associated with a lower risk of type 2 diabetes, according to a new study led by Harvard School of Public Health researchers. Greater consumption of fruit juices was associated with a higher risk of type 2 diabetes.
The researchers examined data gathered between 1984 and 2008 from 187,382 participants in three long-running studies (Nurses' Health Study, Nurses' Health Study II, and Health Professionals Follow-up Study).
The researchers looked at overall fruit consumption, as well as consumption of individual fruits: grapes or raisins; peaches, plums, or apricots; prunes; bananas; cantaloupe; apples or pears; oranges; grapefruit; strawberries; and blueberries. They also looked at consumption of apple, orange, grapefruit, and other fruit juices.
People who ate at least two servings each week of certain whole fruits -- particularly blueberries, grapes, and apples -- reduced their risk for type 2 diabetes by as much as 23% in comparison to those who ate less than one serving per month.
Conversely, 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%. The researchers found that swapping three servings of juice per week for whole fruits would result in a 7% reduction in diabetes risk.
The fruits' glycemic index (a measure of how rapidly carbohydrates in a food increase blood sugar) did not prove to be a significant factor in determining a fruit's association with type 2 diabetes risk. However, the high glycemic index of fruit juice -- which passes through the digestive system more rapidly than fiber-rich fruit -- may explain the positive link between juice consumption and increased diabetes risk.
The researchers theorize that the beneficial effects of certain individual fruits could be the result of a particular component. Previous studies have linked anthocyanins found in berries and grapes to lowered heart attack risk, for example. More research is needed to determine which components in certain fruits influence diabetes risk.
Source: BMJ (British Medical Journal), online August 29, 2013
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