Drinking fruit juice has generally seemed to be a reliable, second-best alternative to eating whole fruits, but researchers from the Harvard School of Public Health (HSPH) have officially put the kibosh on this idea. According to HSPH's new study, drinking fruit juice may increase a person’s risk of type 2 diabetes while eating whole fruits, particularly blueberries, grapes, and apples, has the opposite effect.

"Our data further endorse current recommendations on increasing whole fruits, but not fruit juice, as a measure for diabetes prevention," lead author Isao Muraki, research fellow in the Department of Nutrition at HSPH, said in a press release.

Risky Behavior

The researchers examined data gathered by three long-running studies (Nurses' Health Study, Nurses' Health Study II, and Health Professionals Follow-up Study). Overall, the studies, which are funded by the National Institutes of Health (NIH), include pertinent health-related information on approximately 187,382 participants between the years 1984 and 2008. Those participants who reported a diagnosis of diabetes, cardiovascular disease, or cancer at enrollment were excluded by the researchers, who next examined fruit consumption.

In particular, the researchers investigated participants’ habit of eating whole fruits in general as well as their preference for individual fruits. Furthermore, the researchers examined the type and amount of juice that participants drank, including apple, orange, grapefruit, and other fruit juices.

During the study period, results showed that 12,198 participants, or 6.5 percent, developed diabetes.

Specifically, those who consumed one or more servings of fruit juice each day increased their risk of developing type 2 diabetes by a whopping 21 percent. On the other hand, swapping three servings of juice per week for whole fruits may result in a seven percent reduction of diabetes risk. And for the full preventative effect, if a person eats at least two servings each week of blueberries, grapes, and/or apples, the risk for type 2 diabetes dips by as much as 23 percent in comparison to those who eat less than one serving per month.

"Our findings provide novel evidence suggesting that certain fruits may be especially beneficial for lowering diabetes risk," senior author Qi Sun, assistant professor in the nutrition department at HSPH and assistant professor at Brigham and Women's Hospital, said in a press release.


Oddly, glycemic index — a measure of how rapidly carbohydrates in a food boost blood sugar — did not directly impact whole fruit findings in the current study. For example, when determining a particular fruit's association with type 2 diabetes risk, its individual glycemic index — whether high or low — did not seem to impact the results. Alternatively, the researchers believe it was the high glycemic index of fruit juice, which may explain the increased risk of diabetes.

The researchers also hypothesize anthocyanins found in berries and grapes might be the reason behind the lowered diabetes risk, as that same component appears to lower the risk of cardiovascular disease, according to a 2011 study. Plants typically produce anthocyanins, which are water-soluble pigments that impart, to plants, colors ranging from violet and blue to most shades of red, as a protective mechanism against environmental stress factors, including UV light, cold temperatures, and drought.

Source: Wallace TC. Anthocyanins in Cardiovascular Disease. Advances in Nutrition. 2011.