People who tend to eat mostly plants may be less likely to develop type 2 diabetes, a research review suggests.
Researchers examined data from nine previously published studies with a total of 307,099 participants, including 23,544 people who developed type 2 diabetes. The length of the studies ranged from 2 to 28 years. All of the studies used food frequency questionnaires to assess participants' diets.
Overall, people who most closely adhered to a vegan, vegetarian or other type of plant-based diet were 23 per cent less likely to develop type 2 diabetes than people who consumed the least amount of plant-based meals, researchers report in JAMA Internal Medicine.
"Plant-based diets can promote metabolic health and reduce diabetes risk through many pathways, including preventing excess weight gain, improving insulin sensitivity, reducing inflammation, and other mechanisms," said Dr Qi Sun, senior author of the study and a researcher at the Harvard T.H. Chan School of Public Health and Brigham and Women's Hospital in Boston.
People who eat a healthy variety of plant-based meals can lower their diabetes risk even when they're not strict vegetarians - avoiding meat, poultry and fish - or vegans - also avoiding animal products like milk and eggs.
But they may not benefit as much if their plant-based diet is full of foods like French fries, white bread, and white rice, Sun said by email.
"It does matter what veggies people eat and how the veggies are processed," Sun said. "Therefore, consuming healthy plant foods that are not or minimally processed, such as fresh fruits and vegetables, legumes, nuts, and whole grains, should be emphasised."
People in the study who followed this advice - with the healthiest mix of fruits, vegetables and whole grains in their plant-based diets, were 30 per cent less likely to develop type 2 diabetes than participants who tended to ignore this idea.
Type 2 diabetes, the most common form, is linked to obesity and aging and happens when the body can't properly use or make enough of the hormone insulin to convert blood sugar into energy. Left unchecked, diabetes can lead to serious complications like nerve damage, blindness, amputations, kidney damage and heart problems.
Doctors typically advise patients with type 2 diabetes to follow a low-calorie, low-fat and low-carbohydrate diet that includes lots of fresh fruits, vegetables and whole grains as well as lean poultry and fish. Fatty, sugary foods are discouraged along with consuming too much red or processed meat.
None of the smaller studies in the current analysis were controlled experiments designed to prove whether a plant-based diet helps prevent diabetes or serious complications from the disease.
Still, the results offer fresh evidence of the potential for good eating habits to help prevent and manage diabetes, said Samantha Heller, a nutritionist at New York University Langone Medical Center in New York City.
"Adding more whole plants such as broccoli, edamame, quinoa, extra virgin olive oil, almonds, and berries, to our diet is a great way to help manage type 2 diabetes and weight," Heller, who wasn't involved in the study, said by email.
"Higher fiber foods are healthy for the gut microbiome, improve gastrointestinal function, improve insulin sensitivity, and help manage blood sugar," Heller added. "However, it is important to remember that even (portion sizes) of healthy foods matter."