Plant-based diet outperforms portion control in new type 1 diabetes study

Switching out animal products with plant-based foods — even those defined as “unhealthy” by the plant-based diet index — has been deemed effective for weight loss in adults diagnosed with type 1 diabetes by a new study. 

The paper published in Frontiers in Nutrition details how participants following a vegan diet lost an average of 11 pounds, compared to a lack of significant weight loss for participants who followed a portion-controlled diet.

“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,” says lead author Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee for Responsible Medicine and lead author.

Investigating vegan weight loss

The new research is a secondary analysis of a Physicians Committee study, which was the first randomized clinical trial to look at a vegan diet in people with type 1 diabetes.

In the 12-week study, 58 adults with type 1 diabetes were randomly assigned to either a low-fat vegan group with no limits on calories or carbohydrates or a portion-controlled group that reduced daily calorie intake for overweight participants and kept carbohydrate intake stable over time.

In this secondary analysis, participants’ dietary records were used to assess the relationship of a plant-based diet index (PDI), healthful PDI (hPDI), and unhealthful PDI (uPDI) with weight loss in adults with type 1 diabetes.

“Healthful” plant-based foods, as defined by the PDI system, include fruits, vegetables, whole grains, nuts, legumes, oils, coffee, and tea.

“Unhealthful” plant-based foods include fruit juice, sugar-sweetened beverages, refined grains, potatoes, and sweets. In each of the categories, a higher score indicates greater consumption of the plant-based foods in that category.

Dietary parameters

In the study, the overall PDI score increased on the vegan diet and did not change on the portion-controlled diet. Meanwhile, the hPDI score increased on both diets, more on the vegan diet.

Also, uPDI increased on the vegan diet and did not change on the portion-controlled diet.

Participants on the vegan diet significantly increased consumption of “healthful” plant foods, including legumes, whole grains, and fruits, while significantly decreasing consumption of vegetable oils and nuts.

On the portion-controlled diet, participants increased their intake of whole grains.

On either diet, the consumption of “unhealthful” plant foods did not change significantly, except for reduced consumption of refined grains on the portion-controlled diet.

Study findings

Participants on the vegan diet lost 5.2 kilograms on average, which was associated with changes in PDI and hPDI scores, while there was no weight change for participants on the portion-controlled diet. Changes in uPDI did not result in changes in weight.

The original study found that a vegan diet also reduced insulin needs, improved insulin sensitivity and glycemic control, and improved cholesterol levels and kidney function in people with type 1 diabetes.

Aside from weight loss, scientists have previously investigated plant-based diets for their impact on weight training. In one study, researchers found that vegan diets during weight training do not impact muscle building. It concluded that following plant- or animal-based diets made no difference in muscle protein synthesis.

Another New Zealand study evaluating protein intake and quality revealed that three in four vegans ate sufficient protein. Still, half didn’t meet daily requirements for the essential amino acids lysine and leucine when accounting for protein digestibility.