An extensive meta-analysis provides comprehensive evidence that consistently following a healthful, plant-based diet could help lower the risk of type 2 diabetes.

According to data from the Centers of Disease Control and Prevention (CDC), more than 100 million adults in the United States have diabetes or prediabetes — the set of conditions that precede the development of type 2 diabetes.

One of the main risk factors for type 2 diabetes — the most common form of diabetes — is diet. However, this is a modifiable entity, meaning that, if a person adopts more healthful dietary habits, they can reduce their risk of developing this metabolic condition.

In recent years, many studies have suggested that vegan, vegetarian, or other plant-based diets could significantly reduce a person's diabetes risk.

Now, a team of researchers from the Harvard T. H. Chan School of Public Health in Boston, MA, has conducted a comprehensive review and meta-analysis of nine studies that considered the association between dietary patterns and the risk of type 2 diabetes.

Between them, these studies involved no fewer than 307,099 participants, among whom 23,544 had type 2 diabetes.

"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," notes the review's first author Frank Qian.

Qian and colleagues report their findings in a paper that appeared yesterday in JAMA Internal Medicine.

Adherence and healthfulness both matter

In their analysis, Qian and team first looked at how adherence to a predominantly plant-based diet of any kind related to diabetes risk. In this scenario, "predominantly plant-based" could mean a diet that centered on both healthful plant foods, including fruits, vegetables, nuts, and legumes, and less healthful ones, such as potatoes and sugars. These types of diets could also include some products of animal origin.

Then, the team assessed the association between diabetes risk and following healthful plant-based diets that featured, primarily, a high amount of healthful fruit, vegetables, legumes, whole grains, and nuts.

The researchers found that, in general, participants who adhered more strictly to plant-based diets had a 23% lower risk of type 2 diabetes than those who presented a less strict adherence to these dietary patterns.

However, they add that the association with a lower risk of type 2 diabetes was even stronger in the case of people who adhered to strictly healthful plant-based diets.

While the researchers have only observed a correlation, they suggest that a causal relationship may underlie it. They also observe that there are several mechanisms that could explain this link.

For one, they note that healthful, plant-based foods can demonstrably improve both insulin sensitivity and blood pressure, each of which plays a role in the development of diabetes. Moreover, plant-based diets can prevent or reduce weight gain, as well as reduce low grade inflammation, two other factors that contribute to a person's risk of diabetes.

"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 health[ful] plant foods as the cornerstone of such diets." Senior author Dr. Qi Sun

While the current research only received grants from national research funding bodies (the National Institutes of Health), some of the authors involved in the review have disclosed potential conflicts of interest.

Thus, one co-author reported receiving individual research support from the California Walnut Commission, as well as honoraria from Metagenics and Standard Process, two companies that produce dietary supplements. Dr. Sun has reported receiving consultancy fees from Emavant Solutions GmbH, a healthcare facilities company.