Vegan diet aids weight loss in adults with type 1 diabetes, study finds

Replacing animal products with plant-based foods can lead to significant weight loss in adults with type 1 diabetes, according to a new study published in Frontiers in Nutrition by the Physicians Committee for Responsible Medicine. The findings suggest that even plant-based foods classified as "unhealthy" by standard dietary indices offer a better alternative than animal-based meals when it comes to weight management.

The study, led by Dr Hana Kahleova, Director of Clinical Research at the Physicians Committee and lead author of the report, analyzed dietary habits and weight outcomes in a randomized clinical trial involving 58 adults with type 1 diabetes. Over 12 weeks, participants followed either a low-fat vegan diet with no caloric or carbohydrate restrictions or a conventional portion-controlled diet aimed at reducing daily calorie intake.

“Our research shows that replacing animal products with plant-based foods – even so-called ‘unhealthy’ ones, as defined by the plant-based diet index – benefits people with type 1 diabetes who are looking to lose weight,” said Kahleova. “Whether you have an orange and oatmeal for breakfast or orange juice and toasted white bread, either option is a better choice for weight loss than eggs and cottage cheese.”

This latest analysis used a scoring system based on the plant-based diet index (PDI), which includes both healthful and unhealthful categories of plant foods. Healthful options – measured by the healthful PDI (hPDI) – included fruits, vegetables, whole grains, legumes, nuts, and unsweetened beverages like tea and coffee. Conversely, the unhealthful PDI (uPDI) captured consumption of foods such as fruit juice, sugar-sweetened drinks, refined grains, sweets, and potatoes.

Participants on the vegan diet saw significant increases in their overall PDI and hPDI scores, indicating greater intake of beneficial plant-based foods. Notably, their uPDI scores also increased slightly, reflecting a broader inclusion of less nutritious plant items – but this did not undermine the overall benefits. The portion-controlled group showed no changes in their PDI or uPDI scores and a smaller increase in hPDI.

On average, participants following the vegan diet lost 5.2kg (approximately 11 lbs), while those in the portion-controlled group did not experience significant weight changes. Weight loss among the vegan group was closely tied to improvements in PDI and hPDI scores, while changes in uPDI had no observable impact on weight.

Alongside weight loss, earlier findings from the same study showed that the vegan diet led to improvements in insulin sensitivity, reductions in insulin requirements, better glycemic control, and enhanced kidney and cholesterol markers.

Further breakdown of eating patterns revealed that the vegan group significantly increased their consumption of legumes, fruits, and whole grains while decreasing intake of nuts and vegetable oils. Meanwhile, participants on the portion-controlled diet only modestly increased whole grain consumption and reduced refined grain intake.

These results add to a growing body of evidence supporting the use of plant-based diets in managing chronic conditions, including diabetes. While previous studies have focused largely on type 2 diabetes, this research is among the first to provide randomized clinical trial data specific to individuals with type 1 diabetes.

The study underscores that even plant-based foods often seen as less healthful can contribute positively when they replace animal-derived options. In doing so, it challenges the assumption that all vegan diets must be strictly composed of whole, minimally processed ingredients to be effective in clinical settings. Instead, the data suggest that the overall shift toward plant-based eating may offer benefits, regardless of the exact composition of the diet.