High glycated hemoglobin A1c (HbA1c) is strongly correlated with developing type 2 diabetes mellitus (T2DM) complications; this study reviews the efficacy of various types of metabolic surgeries in reducing HbA1c levels in type 2 diabetics with BMI <35 kg/m(2). An electronic search of MEDLINE databases using terms 'metabolic surgery', type 2 diabetes mellitus, BMI <35 kg/m(2), and related keywords for studies published between 1987 and 2013. Data from 53 articles with 2,258 patients were selected for this review. The weighted mean change in HbA1c was -2.8 % (95 % CI -2.8 to -2.7, p < 0.01) and weighted mean BMI change was -5.5 kg/m(2) (95 % CI -5.6 to -5.4, p < 0.01). There was a strong correlation between weighted percentage mean change in HbA1c and BMI. Adjustable gastric banding and duodenal jejunal bypass were inferior to other surgeries in reducing BMI and HbA1c in BMI <35 kg/m(2). Metabolic surgery significantly decreases HbA1c in T2DM patients with BMI <35 kg/m(2) and that the magnitude of HbA1c change may be a useful surrogate of DM control.