High-protein vegan and omnivorous diets improve peripheral insulin sensitivity to a similar extent in people with type 2 diabetes

Background: High-protein diets have been recognized as a potential strategy in the nutritional management of type 2 diabetes (T2D). Mycoprotein is a high-fibre, high-protein food ingredient previously shown to improve acute glycaemic control. We determined whether incorporating mycoprotein into a high-protein vegan diet would improve glycaemic control to a greater extent than an isonitrogenous omnivorous diet in people with T2D. Methods: Seventeen adults (f = 5, age = 58.3 ± 8.3 years, BMI = 32.9 ± 4.7 kg∙m⁻², HbA1c = 60 ± 15 mmol∙mol⁻¹) with T2D were randomly allocated to a 5-week eucaloric high-protein (30% energy from protein) diet, either an omnivorous diet (OMNI; 70% protein from omnivorous sources) or an isonitrogenous, mycoprotein-rich, vegan diet (VEG; 50% protein from mycoprotein). Glycaemic control was assessed using a two-step hyperinsulinaemic-euglycaemic clamp (HEC) with D-[6,6-²H₂] glucose infusion, a mixed-meal tolerance test (MMTT) and continuous glucose monitoring. Results: The rate of glucose disappearance (RdT), glucose disposal rate and endogenous glucose production, as well as postprandial time-course of blood glucose, serum insulin and C-peptide were assessed during the HEC and MMTT, respectively. Both groups had improved peripheral insulin sensitivity (intervention effect, p = 0.006; increased RdT/Insulin of 1.0 ± 0.6 and 1.0 ± 0.3 mg kg⁻¹ min⁻¹ in OMNI and VEG, respectively), HbA1c (intervention; p = 0.001) and glycaemic variability (intervention; p = 0.040; increased time in-range of 11.8 ± 9.3% and 23.3 ± 12.9% in OMNI and VEG). There were no improvements in hepatic insulin sensitivity or in postprandial blood glucose and serum C-peptide (p > 0.05) during the MMTT. Conclusions: High-protein diets, whether predicated on vegan or omnivorous proteins, can improve glycaemic control by increasing peripheral insulin sensitivity in people with T2D.