Eating a plant-based diet is linked to lower chances of developing type 2 diabetes, according to a wide-ranging study.
Researchers in the United States analysed nine studies on 307,099 participants with 23,544 cases of type 2 diabetes, using the search terms “vegan”, “vegetarian” and “plant-based diet”.
They said a “significant inverse association” was found between people who followed “plant-based dietary patterns” and the risk of the disease.
They defined “plant-based dietary patterns” as the higher consumption of plant-based foods and lower consumption or exclusion of animal-based foods.
Those who adhered to the definition most strictly were found to have the lowest risk of developing the disease, according to the paper, published in JAMA Internal Medicine.
The link was strengthened when only healthy plant-based foods – including fruits, vegetables, whole grains, legumes and nuts – were used in the definition.
The authors, from Harvard TH Chan School of Public Health, Boston, say they believe the study provides “the most complex evidence on the association between plant-based dietary patterns and incidence of type 2 diabetes”.
In all the studies, the highest category of adherence to plant-based diets, which included vegans and vegetarians, still involved a significant amount of food derived from animals.
More research is needed to determine whether further restrictions yield additional health benefits, they say.
But the authors said they believed it was possible to follow a strict vegan diet without losing out on key nutrients.
They said: “Concerns have been raised that strict vegan diets that exclude dairy and fish may lead to inadequate intakes of certain nutrients in the general populations, including vitamins B12 and D and calcium, consumption of which is associated with lower risk of type 2 diabetes.
“However, consuming animal products is not the only way to prevent nutritional deficiencies for these specific nutrients.
“The consumption of a balanced, plant-based dietary pattern with the inclusion of fortified foods and the use of dietary supplements can help individuals who practice a vegan or vegetarian diet meet their needs for these nutrients.
“The dose-response association observed in our analysis suggests that, in general populations that do not practice strict vegetarian or vegan diets, replacing animal products with healthful plant-based foods is likely to exert a significant reduction in the risk of diabetes.”
Clinical trials have shown diets rich in fruits, vegetables, nuts and wholegrains individually and jointly improve insulin sensitivity and blood pressure and reduce long-term weight gain.
People following these diets tend to avoid red and processed meats, which have been linked with an increased risk of developing the disease.
The authors said not all plant foods were equally beneficial. Unhealthy plant-derived foods, such as refined grains, starches and sugar, were linked to a higher risk of type 2 diabetes.
They advise that dietary guidelines should continue to emphasise the importance of the quality of food types.
They also said the benefits go further than simply weight management, with plant-based diets “improving measures of glycemic control independently of body weight” in people with and without type 2 diabetes.
Dr Ian Johnson, a nutrition researcher and Emeritus Fellow at the Quadram Institute Bioscience, said: “This rigorous statistical analysis of nine previously published prospective studies shows that the more closely the participants approached an entirely plant-based dietary pattern, the lower their risk of developing type 2 diabetes.
“This was particularly true for diets containing large quantities of whole-grain cereals, nuts, fruits and vegetables, rather than foods based on highly refined flour and sugar.
“The benefits may come from reduced consumption of meat and other animal products, from protective effects of plant constituents such as dietary fibre, from a lower risk of overweight and obesity, or perhaps from a combination of all these effects.
“Whatever mechanisms may be at work, this study is consistent with current public health advice to consume substantial quantities of lightly processed plant foods rich in whole-grains and fibre, and to limit consumption of animal products.
“Importantly for the UK, where type 2 diabetes is a rapidly increasing burden on the NHS, this new analysis suggests that any shift toward this type of dietary pattern could be beneficial.”