The Joslin Blog ran a column a few months ago discussing the role of fruit in the diet of those with diabetes. In a salute to serendipity, a recently published analysis of several well-known, long-running observational studies have found evidence to also support the role of fruit in preventing the onset of type 2 diabetes.
It has been well-known for quite some time that people who eat more fruits and vegetables tend to have lower rates of certain cancers and other chronic diseases. The same may also be true when it comes to type 2 diabetes, say the authors of ”Fruit consumption and risk of type 2 diabetes: results from three prospective longitudinal cohort studies.”
The study, published in the British Medical Journal on Aug 29, 2013, looked at the combined results of three longitudinal cohort studies (a cohort is a group defined by a particular characteristic and followed over time)—the Nurses’ Health Study, the Nurses’ Health Study II and Health Professionals Follow-up Study. The data reviewed spanned the years from 1984 to 2009. 187,382 participants were followed for a combined 3,464,641 years of follow-up. During each study, participants were sent food frequency questionnaires every four years that inquired about their intake of ten different fruits, including bananas apples, strawberries, grapes and watermelon.
The authors concluded that the statistical analysis of the data indicates a correlation between higher levels of fruit consumption and a decreased risk of type 2 diabetes. The risk of developing diabetes in the study population was 6.5 percent. The risk of diabetes development was reduced by 7 percent for those who had at least three servings of whole fruits per week.
One of the most interesting things about the results of the analysis was that although whole fruit were winners, the same could not be said for fruit juice. In fact, greater intake of juice was correlated with a higher risk of developing type 2 diabetes.
Why whole fruit eaters were at lower risk than juice drinkers wasn’t studied. Perhaps there is something special in whole fruit that is eliminated, other than fiber, when fruits are squeezed into juice. Perhaps it is that juice drinkers tend take in more calories from their fruit consumption than whole fruit eaters and the excess calories leads to excess weight.
Why fruit itself may protect against diabetes is also a mystery. When scientists have tested specific components of fruits and vegetables (such as fiber and certain vitamins and minerals) to assess their relationship to disease prevention they have come up empty. There appears to be some special property(s) of whole fruits and vegetables that are beneficial only when consumed intact.
American diets, in general, do not meet the recommendations of the 2010 Dietary Guidelines for Americans in terms of consumption of fruits. The median intake of fruit (times per day) ranges from a low of .9 in Mississippi and Oklahoma to a high of 1.3 times in Vermont, New Hampshire, the District of California and California. Nutrition professionals recommend filling half your plate with fruit and vegetables at each meal. Or, in other words, a healthy, active 50 year old should have 1.5 cups of fruit and 2.5 cups of vegetables per day.
These study correlations don’t prove anything— as they say, correlation does not equal causation. But they do give scientists ideas about what they should be looking into. If the same associations pop up again and again there is reason to think there maybe something to them. When all is said and done, it does give some credence to the old adage “an apple a day…