Eating whole fruits can reduce people’s risk of developing type 2 diabetes, according to a new study from researchers at the Harvard School of Public Health—but juicing them can send their risk factors soaring.
Led by Dr. Isao Muraki from the Harvard School of Public Health’s Department of Nutrition, the meta-analysis looked at research gathered through several different studies between 1984 and 2008, and found that during the 25-year period, those 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 percent compared to those who ate less fruit.
The study, which included 3,464,641 participants—12,198 of whom developed type 2 diabetes—also found that those who consumed one or more servings of fruit juice each day increased their risk of developing diabetes by as much as 21 percent. Trading at least three of those juice servings for whole fruits reduced that risk by about 7 percent, researchers said.
“Increasing fruit consumption has been recommended for the primary prevention of many chronic diseases, including type 2 diabetes, although epidemiologic studies have generated somewhat mixed results regarding the link with risk of type 2 diabetes,” the authors wrote. “The inconsistency among these studies may be explained by differences in types of fruits consumed in different study populations as well as difference in participants’ characteristics, study design, and assessment methods, although a meta-analysis did not show that the associations differed by sex, study design, or location.”
Researchers said that when studying whole fruit, the glycemic index- the measurement that determines how quickly a food is transformed into glucose and sent into the blood stream for energy – did not seem to impact the risk factors, although because juice is digested quickly and has a high glycemic index, the numbers could have played a role where juice was concerned.
Researchers theorize that some beneficial component of the fruit, such as fiber, antioxidants or something else, could be tied to a lower risk of diabetes, but more research would be required to determine what components might warrant more research.
The study appeared in late August in the British Medical Journal.
According to the glycemic index chart, fruits including cherries, grapefruits, prunes, grapes, blueberries, dried apricots, apples, canned peaches, fresh pears, plums, strawberries, navel oranges, bananas, fresh peaches, canned pears, grapes, mango, and fruit cocktail are low on the glycemic index.
Moderate options include papaya, raisins, fresh apricots, kiwi, dried figs, pineapple and cantaloupe, while watermelon and dates are at the high end of the scale.