People who follow predominantly plant-based diets with greater adherence may have a lower risk of developing type 2 diabetes than those who follow these diets with lower adherence, according to a new meta-analysis from Harvard T.H. Chan School of Public Health. The researchers also found that the association was stronger for people whose diets emphasized healthy plant-based foods.
The study will be published online July 22, 2019 in 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 first author Frank Qian, who conducted the research as a masters student in the Department of Nutrition.
While previous studies have suggested that plant-based dietary patterns may help lower type 2 diabetes risk, there has been a lack of research analyzing the overall body of epidemiological evidence. According to the researchers, the current study provides the most comprehensive evidence to date for the association between adherence to healthy plant-based diets and reduced type 2 diabetes risk.
The researchers 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. They 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 researchers 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.
The researchers 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, according to the researchers, 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 senior author Qi Sun, associate professor in the Department of Nutrition.
Other Harvard Chan authors of the study included Gang Liu, Frank Hu, and Shilpa Bhupathiraju.