High-protein diet vs. Mediterranean diet for improving insulin resistance Original paper

A high-protein diet (HP) and a Mediterranean diet (M-diet) have been linked to weight loss and improved health outcomes, including a reduced risk of type 2 diabetes.^[1][2] Is one better than the other for improving markers of insulin resistance?

In this 10-day randomized crossover trial, 20 women (average age of 37) with insulin resistance and obesity consumed two hypocaloric (fewer calories than are burned) diets with equal energy content: M-diet (55% carbohydrate, 25% fat, and 20% protein) and HP (40% carbohydrate, 30% fat, and 30% protein). There was no washout period between diets.

The primary outcomes were fasting insulin, homeostatic model assessment of insulin resistance (HOMA-IR), and glycemic variability (the number of blood sugar swings throughout the day), measured as the daily mean standard deviation of glucose levels during continuous glucose monitoring. The secondary outcomes were blood sugar parameters, assessed by continuous glucose monitor (average blood sugar level and the percentage of time spent within, above, and below target range); body weight; blood pressure; and diversity in the gut microbiome (on the Shannon and Simpson indexes), assessed using fecal samples.

Fasting insulin (−3.50 µIU per milliliter) and HOMA-IR (−1.0) decreased with HP but increased with M-diet (+1.55 µIU/mL and +0.32, respectively). Moreover, glycemic variability was better with HP than with M-diet (14.8 vs. 17.9 milligrams per deciliter), as was the average blood sugar level.

Both diets reduced body weight and blood pressure and altered gut microbiome composition to a similar extent. Changes in Eubacterium xylanophilum, Desulfovibrio, and Terrisporobacter genera were associated with the positive effect of HP on glycemic variability.

This study is limited by a small sample size, a short intervention period, and the absence of a washout. Also, despite the inclusion of many outcomes, the researchers did not adjust for multiple comparisons, which increases the risk of false-positive results. The findings should be considered exploratory.