Glycine supplementation during six months does not alter insulin, glucose or triglyceride plasma levels in healthy rats

Nowadays, glycine is used in nutritional supplements and to attenuate chronic complications of diabetes and obesity; however, its use has side effects as insulin resistance. Our aim was to evaluate the effect of chronic glycine supplementation on insulin, glucose and triglyceride levels in healthy Wistar rats. Groups were: Control (C), that received sterilized water only, glycine (GG), that received 1% glycine and taurine (TG), that received 0.5% taurine during 6 months (n = 10). Our results showed no differences in plasma insulin levels after six months of supplementation (C: 13.22 +/- 2.0; GG: 11.4 +/- 2.0; TG: 11.13 +/- 2.0 ng/ml; p = 0.64). Likewise, neither glucose plasma concentration (C: 99.9 +/- 3.9 mg/dl; GG: 104.3 +/- 4.3 mg/d TG: 104.5 +/- 4.8 mg/dl) (p = 0.88) nor triglyceride levels (C: 58.4 +/- 5.6 mg/dl; GG: 46.9 +/- 2.3 mg/dl: TG: 50.68 +/- 3.3 mg/dl), showed differences after six months supplementation (p = 0.22). Furthermore, the analysis of glycine (C: 80 +/- 24.6: GG: 83.9 +/- 25.9: TG: 90.7 +/- 13.5 nmol/ml) (p = 0.19) and taurine (C: 169 +/- 15.17: GG: 148.7 +/- 23.9: TG: 165.8 +/- 22.5 nmol/ml) (p = 0.4) in the plasma of animals with supplementation showed no significant changes. Additionally, general urine tests and histological analysis of liver or kidneys showed no alterations. In conclusion, chronic supplementation with 1% glycine did not have any significant detrimental side effects in our model. However, more studies are still necessary to evaluate the effect of 1% glycine supplementation in humans.