Weighing up the evidence: Plant-based diets and type 2 diabetes

With diet known to play a role in the development of type 2 diabetes, could plant-based nutrition actually help to reduce that risk? 

Lifestyle factors such as diet and exercise are known to be important in the development of type 2 diabetes. Following the publication of a systematic review in 2020 that included over a million people with type 2 diabetes, the impact of lifestyle modification became even clearer.

Among those with the healthiest lifestyle, there was a 75 per cent lower risk of developing type 2 diabetes when compared to the least healthy lifestyle. Adopting a healthy lifestyle among those who already had the disease also reduced the risk of diabetes complications. So what constitutes a healthy diet for those with type 2 diabetes? 

The NHS suggests that people with type 2 diabetes should eat a wide range of foods, including fruit, vegetables, and some starchy foods like pasta, potatoes and rice. Though eating more fruits and vegetables is considered to be part of a healthy diet, are there additional benefits from switching to a purely plant-based diet? 

While the fact that vegetarian diets provide metabolic advantages for the prevention and treatment of type 2 diabetes has been known for some time, by 2018 a review concluded that the benefits of vegetarian diets in the prevention and treatment of type 2 diabetes had become well established.

How does a vegetarian diet work?

While reductions in body weight can lower the risk for type 2 diabetes among those eating a plant-based diet, are there are any additional factors at play? Furthermore, to what extent does the quality of a plant-based diet matter? 

These were the questions addressed in a recent cohort study using data from the participants in the UK Biobank. This database represents a treasure trove for researchers and contains information on genetics, lifestyle and a wealth of other health-related statistics that is regularly provided by over half a million UK individuals. 

For the purposes of the study, researchers used two metrics to define the quality of a plant-based diet. These were defined by ‘healthful’ and ‘unhealthful’ plant-based indices.

For example, when someone stated they ate whole fruits, this added to their healthy plant-based score. In contrast, for an individual reporting they drank fruit juices, this added to their unhealthy score. 

Researchers then looked for any association between the two scores and the risk of type 2 diabetes. The team also assessed if there was any link with factors such as waist circumference, body mass index, an individual’s genetic risk of type 2 diabetes as well as inflammatory biomarkers such as C-reactive protein and measures of liver and kidney function.

A total of 113,097 people were followed for a period of 12 years, during which 2,628 developed type 2 diabetes. In those with the highest compared to the lowest level of a healthy plant-based diet, the risk of developing type 2 diabetes was reduced by 24 per cent.

But this risk was not only due to a lower waist circumference and BMI; there were also lower levels of C-reactive protein and other markers of liver and kidney health. 

Conversely, for those with the highest unhealthy plant-based diet scores, there was a 37 per cent higher risk of developing type 2 diabetes. In other words, the lower risk of developing type 2 diabetes from following a healthy plant-based diet is not just because of reductions in weight but also improvements in liver and kidney function. 

Advice for patients

As the Biobank study was observational, it is not possible to say for certain that switching to a plant-based diet reduces the risk of developing type 2 diabetes.

Nevertheless, abundant other evidence shows that a vegetarian dietary pattern improves glycaemic control and many other markers in patients with type 2 diabetes. 

In light of the currently available evidence, it would seem sensible to suggest that patients either with type 2 diabetes or at risk of developing the condition, might benefit from adopting a high-quality plant-based diet.