A low-fat vegan diet with no restrictions on calories or carbohydrates led to significant reductions in insulin use and body weight among adults with type 1 diabetes (T1D), lowering daily insulin costs compared with a standard portion-controlled diet, according to new research.

“This lower insulin use on the low-fat vegan diet reflects a marker of improved cardiometabolic health and of reduced treatment costs, in addition to the likelihood of lower food costs,” the authors, from the Physicians Committee for Responsible Medicine, wrote in their study published in BMC Nutrition.

The findings are from a secondary analysis of a prior randomized clinical trial published in Clinical Diabetes, which compared a low-fat vegan diet with a portion-controlled non-vegan diet.

Weight Loss and Insulin Reduction

The study included 58 adults with T1D randomly assigned 1:1 to follow either a low-fat vegan or portion-controlled diet for 12 weeks.

Under the vegan diet, participants refrained from consumption of any animal products, eating only plant-based foods, while minimizing added fats, with a total fat intake ≤ 30 g/d.

The portion-controlled diet focused on portion size and keeping carbohydrate intake steady. Those who were overweight reduced daily calories by 500-1000 kcal, with 60%-70% of energy derived from carbohydrates and monounsaturated fats, 15%-20% from protein, < 7% from saturated fat, and < 200 mg of cholesterol per day.

Both groups received support from registered dietitians and met weekly online.

Diet adherence was similar in both groups. At the end of the 12-week study, those following the vegan diet had a body weight reduction of 5.2 kg from baseline (P < .001) compared with a nonsignificant reduction in the portion-controlled group (between-group treatment effect, 1.6 kg/m²; P < .001).

Notably, the total insulin dose in the vegan group decreased by 28% from baseline (mean change, -12.1 units per day; P = .007), whereas there was no change in the portion-controlled group (P = .046).

Neither group had increases in hypoglycemia or hyperglycemia. Despite the lower insulin use, A1c reductions were similar between the vegan and portion-controlled groups (-0.8% vs -0.6%, respectively; P = .34).

The authors attributed the lower insulin use with the vegan group to improvements in insulin sensitivity from reduced liver and muscle fat.

In a previous study, the same research team found a 34.4% decrease in liver lipid levels and a 10% reduction in muscle fat in individuals following a low-fat vegan diet, with the changes correlating with improved insulin sensitivity.

Impact on Costs

Using 2024 insulin pricing, the significant reduction in daily insulin use in the vegan group translated into a 27% decrease in costs, or a savings of $1.08 per day (P = .003). There was no significant change in insulin costs in the portion-controlled group.

Patients with T1D typically face higher treatment costs than those with type 2 diabetes (T2D). In one analysis of 12,687 UnitedHealthcare patients with T1D (2015-2017), the average yearly costs were $18,800 per person, approximately $4600 higher than for those with T2D.

Insulin costs have recently declined significantly due to voluntary manufacturer price reductions and the Inflation Reduction Act of 2022, capping the out-of-pocket cost of insulin at $35 per month for Medicare beneficiaries. However, study first author Hana Kahleova, MD, PhD, of the Physicians Committee for Responsible Medicine in Washington, DC, noted that “the difference in costs for type 1 and type 2 diabetes is likely similar today [as seen in the UnitedHealthcare study].”

Despite the cost-capping efforts, “diabetes is a costly disease, and insulin makes up a good portion of these expenses,” Kahleova told Medscape Medical News.

Vegan Diet’s Benefits Seen Across Conditions

Kahleova noted that the group’s previous studies have shown that a low-fat vegan diet led to similar weight reductions in other populations, including postmenopausal women and people with rheumatoid arthritis and other conditions.

“Our clinical research studies regularly show that participants in the vegan group achieve greater weight loss than those in the group who make no diet changes or consume animal products,” she said.

The diet’s emphasis on more fiber and little fat is filling without adding extra calories, Kahleova explained.

“Our previous research also shows that a vegan diet actually increases post-meal metabolism, which helps burn calories.”

Potential longer-term benefits associated with improvements in insulin sensitivity and glycemic control include cardiovascular and kidney health improvements, she added.

“The take-home message for clinicians is that they should recommend that patients with type 1 diabetes try a vegan diet to not only reduce insulin use — but to achieve a healthy weight, improve heart and kidney health, and realize other possible health benefits associated with a plant-based diet,” Kahleova said.

The study was funded by the Physicians Committee for Responsible Medicine and supported by a grant from the Institute for Technology in Health Care. Kahleova reported receiving compensation from the Physicians Committee for Responsible Medicine for her work on this study.