Plant-based dietary patterns — especially when they are enriched with healthful plant-based foods (such as fruits, vegetables, whole grains, legumes, and nuts) — are beneficial for the primary prevention of type 2 diabetes, according to a systematic review and meta-analysis of previous observational studies, published online this month in the JAMA Internal Medicine.

“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,” said Frank Qian, a researcher at the Harvard T.H. Chan School of Public Health.

Qian and colleagues conducted a systematic review and meta-analysis of prospective studies to assess the association between plant-based dietary patterns and the risk of type 2 diabetes.

They identified nine studies that looked at this association and were published through February 2019.

Their meta-analysis included health data from 307,099 participants with 23,544 cases of type 2 diabetes.

The team analyzed adherence to an ‘overall’ predominantly plant-based diet, which could include a mix of healthy plant-based foods such as fruits, vegetables, whole grains, nuts, and legumes, but also less healthy plant-based foods such as potatoes, white flour, and sugar, and modest amounts of animal products.

The scientists also looked at ‘healthful’ plant-based diets, which were defined as those emphasizing healthy plant-based foods, with lower consumption of unhealthy plant-based foods.

They found that people with the highest adherence to overall predominantly plant-based diets had a 23% lower risk of type 2 diabetes compared to those with weaker adherence to the diets.

They also found that the association was strengthened for those who ate healthful plant-based diets.

One mechanism that may explain the association between predominantly plant-based diets and reduced type 2 diabetes risk is that healthy plant-based foods have been shown to individually and jointly improve insulin sensitivity and blood pressure, reduce weight gain, and alleviate systemic inflammation, all of which can contribute to diabetes risk.

“Overall, 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,” said Dr. Qi Sun, from the Harvard T.H. Chan School of Public Health and the Brigham and Women’s Hospital and Harvard Medical School.

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Frank Qian et al. Association Between Plant-Based Dietary Patterns and Risk of Type 2 Diabetes: A Systematic Review and Meta-analysis. JAMA Intern Med, published online July 22, 2019; doi: 10.1001/jamainternmed.2019.2195