Eating a plant-based diet was tied to a reduced risk for developing type 2 diabetes, according to a review.
Pooled data from nine observational studies indicated that high adherence to a plant-based diet was associated with a 23% lower risk for incident type 2 diabetes versus poor adherence to such a diet (95% confidence interval [CI] -29% to -16%), reported Qi Sun, MD, ScD, of Harvard T. H. Chan School of Public Health in Boston, and colleagues.
Writing in JAMA Internal Medicine, the researchers reported modest heterogeneity among the studies included in the meta-analysis (I2=44.5%, P=0.07 for heterogeneity). They also found similar outcomes when using a fixed-effects model for computing relative risk (RR 0.80, 95% CI 0.75-0.84).
Among the studies with a stricter, arguably healthier definition of a plant-based diet — one comprising only of fruits, vegetables, whole grains, nuts, and legumes — the point estimate for diabetes risk reduction was somewhat great (RR 0.70, 95% CI 0.62-0.79).
Lead author Frank Qian, MPH, also at the Chan School, said in a statement, “Plant-based dietary patterns are gaining popularity in recent years, so we thought it was crucial to quantify their overall association with diabetes risk, particularly since these diets can vary substantially in terms of their food composition.”
And based upon these findings, senior author Sun said that “these data highlighted the importance of adhering to plant-based diets to achieve or maintain good health, and people should choose fresh fruits and vegetables, whole grains, tofu, and other healthy plant foods as the cornerstone of such diets.”
For the systematic review, the research team scanned the major databases for studies addressing links between plant-based diets and incidence of type 2 diabetes in adults. Such diets could include vegetarian and vegan diets as well as others with animal-based foods at low levels. However, the group’s relatively loose definition of plant-based diets also encompassed less-than-healthy foods, such as sugars, refined grains, and sweetened-beverages.
The meta-analysis then included nine cohorts from seven published studies, including data on over 307,000 adults and 23,544 cases of incident type 2 diabetes. Follow-up periods in these studies ranged from 2 to 28 years and mean baseline BMIs were 23 to 26.7.
In subgroup analysis conducted by Sun’s team, the relationship between a plant-based diet and relative risk reduction in incident type 2 diabetes was still apparent. Specifically, the group found significant diabetes risk reductions when the pooled cohort was stratified by age — 55 years and older (RR 0.85, 95% CI 0.78-0.92) and younger than 55 (RR 0.77, 95% CI 0.70-0.84) — and by sex — male (RR 0.81, 95% CI 0.76-0.87) and female (RR 0.80, 95% CI 0.72-0.89).
When cohorts were broken down by global region, high adherence to a plant-based diet was associated with reduced diabetes risk: North America: RR 0.78 (0.73-0.84), Europe: RR 0.82 (95% CI 0.65-1.02), and Asia: RR 0.82 (95% CI 0.74-0.89).
Sun and colleagues said the most likely mechanism behind the association is that components of the plant-based diets improve insulin sensitivity, blood pressure, reduce inflammation, and help to maintain a healthy weight. Such diets are also typically low in cholesterol and L-carnitine.
“Moreover, plant-based diets may also improve the profile of adiposity-related risk markers, including leptin, adiponectin, high sensitivity C-reactive protein, and interleukin-6,” they added.
But people don’t necessarily have to eliminate animal products entirely to enjoy such benefits, the group noted. Their findings are “broadly consistent” with associations seen with “several other dietary patterns that also emphasize plant-based foods but do not completely exclude animal foods, including the Mediterranean dietary pattern, the Dietary Approaches to Stop Hypertension (DASH) pattern, and the Alternative Healthy Eating Index,” they wrote.
Some limitations to the meta-analysis included the lack of randomized clinical trials, and reliance on studies using self-reported diet data and food frequency questionnaires.