( UPDATED September 4, 2013 ) Eating certain whole fruits may reduce the risk for type 2 diabetes, according to the results of 3 combined prospective longitudinal cohort studies.
However, juice consumption may up the risk for diabetes, Isao Muraki, PhD, MD, from the Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts, and colleagues report in an article published online August 29 in BMJ.
"Increasing fruit consumption has been recommended for the primary prevention of many chronic diseases, including type 2 diabetes, although epidemiologic studies have generated somewhat mixed results regarding the link with risk of type 2 diabetes," the authors write. "The inconsistency among these studies may be explained by differences in types of fruits consumed in different study populations as well as difference in participants' characteristics, study design, and assessment methods, although a meta-analysis did not show that the associations differed by sex, study design, or location."
To get a better assessment of the role fruit might have in diabetes risk, the investigators combined data from 3 studies: the Nurses' Health Study (n = 66,105), Nurses' Health Study II (n = 85,104), and Health Professionals Follow-up Study (n = 36,173).. Participants in all 3 studies completed questionnaires assessing health and lifestyle factors, including diet, every 2 years.
The researchers excluded participants with a baseline diagnosis of diabetes, cardiovascular disease, or cancer, as well as those who had missing data for fruit or fruit juice consumption or an extremely high or low caloric intake, and those who had an unclear date of diabetes diagnosis.
Over the course of 3,464,641 person-years of follow-up, 12,198 participants developed type 2 diabetes. In a multivariate analysis adjusted for personal, lifestyle, and dietary risk factors for diabetes, every 3 servings of fruit per week were associated with a lower risk for type 2 diabetes (hazard ratio [HR], 0.98; 95% confidence interval [CI], 0.96 - 0.99).
When the researchers looked at individual types of fruit in a multivariate analysis, adjusted for the same factors, they found that 3 servings per week of some fruits were more closely associated with reduced risk than others:
blueberries: HR, 0.74; 95% CI, 0.66 - 0.83;
grapes and raisins: HR, 0.88; 95% CI, 0.83 - 0.93;
apples and pears: HR, 0.93; 95% CI, 0.90 - 0.96;
bananas: HR, 0.95; 95% CI, 0.91 - 0.98; and
grapefruit: HR, 0.95; 95% CI, 0.91 - 0.99.
Conversely, the intake of cantaloupe (HR, 1.10; 95% CI, 1.02 - 1.18) or fruit juice (HR, 1.08; 95% CI, 1.05 - 1.11) was associated with an increase in the risk for type 2 diabetes.
In a secondary analysis, the investigators found that the consumption of high glycemic load fruits was linked to a lower risk for type 2 diabetes (HR, 0.93; 95% CI, 0.91 - 0.96), whereas consumption of moderate glycemic index fruits was inversely related to risk (HR, 0.94; 95% CI, 0.90 - 0.97).
Limitations of the study included inevitable errors in the estimation of fruit consumption, recall bias, and low ethnic diversity among the study participants.
"Our findings suggest that there is significant heterogeneity in the associations between individual fruits and risk of type 2 diabetes," the authors write. "Overall, these results support recommendations on increasing consumption of a variety of whole fruits, especially blueberries, grapes, and apples, as a measure for diabetes prevention."
The study received funding from the National Institutes of Health. The authors have disclosed no relevant financial relationships.
BMJ. Published online August 29, 2013.
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