People who stick to plant-based diets may have a lower risk of developing Type 2 diabetes compared to those who follow these diets with lower adherence by 23% according to new research from Harvard T.H. Chan School of Public Health.
“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,” says 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.
How was the Study Conducted?
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.
Depending on the goal of the individual studies included in the meta-analysis, the best adherence to a plant-based diet is either the practice of vegan or vegetarian diets or the best score of plant-based eating index, which summarizes how “close” the diet is to vegan or vegetarian diets, Dr. Qi Sun, associate professor in the Department of Nutrition and senior author of the study tells dLife.
For the index, the more plant-based foods in the diet, the higher the score.
Sun explains in studies that used the index to measure adherence to plant-based diets, there’s no black-or-white, clear-cut answer about what foods are allowed or not allowed.
“Instead it has a relative interpretation. A plant-based diet should be, in general, low in animal product intake and high in plant food intake, says Sun.
Having said this, Sun says it’s also necessary to emphasize what foods shall be encouraged and what foods should be discouraged:
A healthy plant-based diet should include lots of fresh fruits and vegetables, whole grains, legumes, nuts, and coffee and use vegetable oils for cooking and should exclude red meats, processed meats, refined carbohydrates, sugar-sweetened beverages, and the use of animal fat for cooking or baking.
“Most people do not practice strict vegan or vegetarian diets, but people shall be smart about what animal proteins that they eat,” says Sun. “Healthy animal products, such as fish or yogurt, can very nicely complement the diets that primarily consist of healthy plant-based foods.”
What were the Findings?
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.
The reason for 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,” says Sun.
The authors note several limitations to the study.
First, all of the diets were assessed using self-reports through questionnaires, which the authors note have inherent measurement errors and misclassifications, particularly because most of the studies did not conduct repeated assessments of diet.
In addition, the authors note that all of the studies were observational.
They note that future studies could study whether other demographic or clinical characteristics, including medical history, may modify the association between plant-based dietary patterns and risk of Type 2 diabetes.
“Our meta-analysis included only studies from relatively high-income countries, and the findings may not be generalizable to populations following plant-based dietary patterns in low- or middle-income countries, where the food quality and composition may differ substantially,” the authors conclude.
As far as how other common low-carb diets, such as the keto diet, compared to plant-based diets in relation to diabetes, Sun says the jury isn’t out yet.
“Most of us will say we don’t have solid evidence to suggest whether the long-term practice of ketogenic diets are better or worse than other diets just yet,” he says, “But we do know that Mediterranean diet, DASH diet, and healthy plant-based diet are robustly associated with lower risk of developing T2D and therefore shall be recommended to folks who want to keep their diabetes risk at bay.”
The researchers received grants from the National Institutes of Health and the National Institute of Diabetes and Digestive and Kidney Diseases. For a complete list of conflict of interest/funding disclosures, view the link to the study below.
The study is published in JAMA Internal Medicine.
- Harvard T.H. Chan School of Public Health. (2019, July 22). Following a healthy plant-based diet may lower Type 2 diabetes risk. EurekAlert! Retrieved July 22, 2019, from https://www.eurekalert.org/pub_releases/2019-07/htcs-fah071819.php