HBA1 and diabetes mellitus: A meta-analysis that included 13 studies found that high protein diets (protein to energy ratio between 25% and 33%) did not significantly reduce HbA1 c levels (%) in patients with diabetes over a period of 12 weeks to 52 months (−0.05 (95% CI (−0.18 to 0.08, p = 0.92))) [17].