Evidence suggests that a high-protein diet promotes superior improvements in glycemic control than a lower-protein, higher-carbohydrate diet. In two 6-month randomized controlled trials that provided all meals to participants, a high-protein diet (30% of energy from protein, 40% from carbohydrate, 30% from fat) and a high-carbohydrate diet (15% of energy from protein, 55% from carbohydrate, 30% from fat) facilitated similar weight loss, and both diets facilitated improvements in markers of glycemic control and beta-cell function compared to baseline, but improvements were greater with the high-protein diet.[1][2] Furthermore, in one of these studies, which only included participants with prediabetes, 100% of participants in the high-protein diet group no longer met the criteria for prediabetes at the end of the study, while only 33% of participants in the high-carbohydrate diet group accomplished this feat.[2] This result may be a consequence of body composition differences: lean mass percentage increased in the high-protein group, while it decreased in the high-carbohydrate group, despite similar weight loss.
In support of these findings, an acute (2-day intervention) crossover trial in people with prediabetes or normal glucose levels found reduced postprandial glucose levels with a high-protein diet compared to a high-carbohydrate diet.[3] The beneficial effects of a high-protein diet on glycemic control may be due to protein’s ability to enhance the secretion of incretin hormones[2][3] — glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) — which potentiate insulin secretion and increase glucose disposal.[4]