In this prospective longitudinal cohort study, investigators studied data from healthcare professionals to understand the impact of fruit consumption on the risk of patients developing type 2 diabetes. They found that greater consumption of specific whole fruits—particularly blueberries, grapes, and apples—is significantly associated with a lower risk of type 2 diabetes, but greater consumption of fruit juice is associated with a higher risk.
Muraki I, Imamura F, Manson JE, et al. Fruit consumption and risk of type 2 diabetes: results from three prospective longitudinal cohort studies. BMJ. 2013 Aug 28;347:f5001. Erratum in: BMJ. 2013 Dec 4;347:f6935.
Prospective longitudinal cohort study
Data were collected from 66,105 women from the Nurses’ Health Study (1984-2008); 85,104 women from the Nurses’ Health Study II (1991-2009); and 36,173 men from the Health Professionals Follow-up Study (1986-2008). All participants were free of major chronic diseases (eg, cancer, cardiovascular disease, diabetes) at baseline.
Using data from 3 prospective cohort studies, researchers estimated the effects of consuming individual fruits, fruit groups (based on glycemic index and load), and fruit juice in relation to the risk of developing type 2 diabetes mellitus (DM-2).
Incident cases of DM-2, identified through self-report and confirmed by supplementary questionnaires
The data suggest that consuming whole fruit lowers the risk of developing DM-2. For every 3 servings of fruit consumed per week, the risk of developing diabetes decreased by 2%.
Certain fruits had greater or lesser impact on overall diabetes risk. When adjusting for individual fruits for every 3 servings per week, blueberries decreased risk by 26%, grapes and raisins by 12 %, prunes by 11%, apples and pears by 7%, and bananas by 5%. Grapefruit did not have a statistically significant impact on DM-2 risk, but cantaloupe increased risk by 10%. Differences in glycemic index/glycemic load values of each fruit did not account for these differences.
Drinking 3 servings of fruit juice each week increased the risk of developing DM-2 by 8%.
This study provides better guidelines to direct the dietary choices for those patients at high risk for developing DM-2. We can now advise patients that drinking fruit juice just 3 times a week can increase the chances of developing diabetes and eating certain whole fruits may help prevent it.
This study implies that, due to the variety of phytochemical compounds, all fruits are not created equal.
This may not seem like much of a surprise given that fruit juice is devoid of the soluble fiber that helps to decrease the absorption of glucose into the bloodstream.1 Lack of fiber in fruit juice leads to faster and greater changes to serum glucose and insulin levels.2 While we might think this explains the increased risk of developing diabetes from juice consumption, the authors suggest that the difference in risk from whole fruit does not have anything to do with differences in glycemic impact. Rather, it likely has to do with the different types and quantities of phytochemicals contained in each fruit. Anthocyanins reduce the amount of glucose produced in the liver.3 We should consider levels of resveratrol, chlorogenic acid, and naringin in individual fruits as well. This study implies that, due to the variety of phytochemical compounds, all fruits are not created equal.
The data collected were based on recall questionnaires, which have inherent recall bias. Recall bias may be of particular concern here given that the 3 cohorts were comprised solely of health professionals. This implies the participants have a better than average knowledge of what “should” be eaten. So while the cohort of participants is large, it may not represent the average American.
[Editor’s note: A correction to this publication was published in the same journal (see erratum notation above). This correction led to a slight variation in the data but did not negate any significant findings nor did it change the conclusion of the study. It is the view of the
Natural Medicine Journal that the correction does not lessen the clinical utility of the study. Please refer to the correction itself for detailed information.]