A new study has found that eating healthy plant-based food and drink, such as fruit, vegetables, nuts, legumes and even coffee, can help lower the risk of developing type two diabetes (T2D).

The research, published in Diabetologia, and conducted by the Department of Nutrition, Harvard T.H. Chan School of Public Health, aimed to identify the benefits of different plant-based diets and investigate possible associations between this and the risk of developing T2D.

Over 90 percent of diabetes cases in the UK alone are the type two form, and the condition is common around the world. Global prevalence of the disease in adults has more than tripled in less than two decades, with cases increasing from around 150 million in 2000 to over 450 million in 2019 and projected to rise to around 700 million in 2045, according to the study.

The researchers of the study suggest that plant-based diets – especially healthy ones rich in foods such as whole grains, fruits and vegetables – have been associated with a lower risk of developing T2D but add that the underlying mechanisms involved are not fully understood.

The team conducted an analysis of blood plasma samples and dietary intake of over 10,000 participants.              

Study participants completed food frequency questionnaires (FFQs) which were scored according to their adherence to three plant-based diets: an overall Plant-based Diet Index (PDI), a healthy Plant-based Diet Index (hPDI), and an Unhealthy Plant-based Diet Index (uPDI). The team distinguished between healthy and unhealthy plant foods according to their association with T2D, cardiovascular disease, certain cancers, and other conditions, including obesity and high blood pressure.

The researchers tested blood samples taken back in the late 1980s and 1990s, in the early phase of the three studies mentioned, to create metabolite profile scores for the participants, and any cases of T2D during the follow-up period of the study were recorded. Analyses of these data together with the diet index scores enabled the team to find any correlations between diets and the risk of developing T2D.

The study found that compared with participants who did not develop T2D, those who were diagnosed with the disease during follow-up had a lower intake of healthy plant-based foods. In addition, they had a higher average BMI, and were more likely to have high blood pressure and cholesterol levels, use blood pressure and cholesterol drugs, have a family history of diabetes, and be less physically active.

Further analysis revealed that after adjusting for levels of trigonelline, hippurate, isoleucine,  and triacyglycerols (TAGs), the association between plant-based diets and T2D largely disappeared, suggesting that they might play a key role in linking those diets to incident diabetes. Trigonelline, for example, is found in coffee and has demonstrated beneficial effects on insulin resistance in animal studies, while higher levels of hippurate are associated with better glycaemic control, enhanced insulin secretion and lower risk of T2D. The team suggest that this could be investigated further and may provide better explanations of how plant-based diets can have a beneficial effect on T2D risk.

Since they only collected blood samples at one point in time, the authors also believe that long-term repeated metabolomics data are needed to understand how dietary changes relate to changes in metabolome, thereby influencing T2D risk.

“While it is difficult to tease out the contributions of individual foods because they were analysed together as a pattern, individual metabolites from consumption of polyphenol-rich plant foods like fruits, vegetables, coffee, and legumes are all closely linked to healthy plant-based diet and lower risk of diabetes,” said Professor Frank Hu, lead author of the study.

“Our findings support the beneficial role of healthy plant-based diets in diabetes prevention and provide new insights for future investigation”, the authors concluded.