10/18/2013 12:54 pm ET Updated Dec 18, 2013

Forbidden Fruit: The Good and The Bad Fruits

The question "What should I eat?" seems remarkably basic. In the animal kingdom, humans are the only ones who seem baffled about this. And there's good reason.

Every few years dietary advice changes. What was good for you last year often turns out to be this year's toxic food. To complicate things further, antiquated science and big business interests produced biased recommendations. Recent attempts to correct this history can be seen in the government's scrapping of the old food pyramid and creation of "The New Food Pyramid" and Harvard's "Healthy Eating Plate." Both of these visual directives to the dietary dilemma place fruit in the healthy column. Harvard's MyPlate recommends eating plenty of fruits, filling half your plate with vegetables and fruits.

While fruit has enjoyed a privileged position in this discussion recent research suggests that not all fruit is created equal.

Investigators gathered data from three large prospective longitudinal cohort studies: the "Nurses' Health Study" (66,105 women from1984-2008); the "Nurses Health Study II"(85,104 women from 1991-2009); and the "Health Professionals Follow-Up Study" (36,173 men from 1986-2008). Their objective was to determine whether certain fruits were more likely to cause Type 2 diabetes (T2DM). All subjects entered the study in a healthy state. Adjustments were made for personal, lifestyle and other dietary risk factors of diabetes when the data was interpreted.

Let's cut to the chase. Blueberries, grapes, apples, bananas and grapefruit were significantly associated with lower risk of T2DM. Fruit juice consumption was associated with an increased risk. The substitution of whole fruits for fruit juice was associated with lower risk for all fruits except strawberries and cantaloupe.

Interestingly, differences in glycemic index/glycemic load did not explain the association of specific fruits with risk of T2DM.

This is a sobering piece of research. Once again we must admit how little we know about one of the most basic questions.

For more by Paul Spector, M.D., click here.

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