For years, nutritionists have debated whether fruit—rich in natural sugars—has a net positive or net negative impact on type 2 diabetes risk. Now a Harvard School of Public Health finding suggests that overall, eating several servings of fruit a week offers slight protection against type 2 diabetes. But certain fruits—blueberries, grapes, and apples—offer greater benefits.
In the study, published online Wednesday in the British Medical Journal, the Harvard researchers examined the dietary habits of more than 187,000 participants involved in three long-term studies and found that people who ate fruit at least three times a week had a 2 percent lower risk of developing type 2 diabetes compared with those who ate less fruit.
Nearly 7 percent of the participants developed type 2 diabetes during the studies, which followed volunteers for more than two decades.
But those who ate three servings a week of blueberries had more than a 25 percent lower risk, while grapes were associated with an 11 percent reduced risk and apples with a 5 percent lower risk.
Drinking fruit juice, on the other hand, slightly raised a person’s risk of developing the disease, and so did eating cantaloupes. Other fruits such as blackberries and raspberries weren’t included in the dietary questionnaire.
Should these results lead us to change our eating habits, choosing, say, blueberries over melon?
No, said study co-author Qi Sun, an epidemiologist. “We don’t want to leave the impression that there’s any magical fruit,” he said, since the study doesn’t prove that eating blueberries actually helps people avoid diabetes.
But the study does point to the need for more research to gain a better understanding of how fruit alters blood sugar levels. For example, it’s long been known that fruit high in fiber is digested more slowly, leading to a slower rise in blood sugar—which is thought to help protect against diabetes. But fruits also contain an array of plant chemicals that can play a role in blood sugar levels.
Blueberries, in particular, are rich in anthocyanins, which have been shown to play a role in how the body metabolizes the blood sugar glucose.
That said, Sun emphasized that eating a daily serving of blueberries won’t provide enough benefits to overcome a lack of exercise, excess body weight, or smoking, which all have a bigger impact on type 2 diabetes risk than fruit consumption.