Glycine Metabolism and Its Alterations in Obesity
and Metabolic Diseases
Received: 10 May 2019; Accepted: 12 June 2019; Published: 16 June 2019
Abstract: Glycine is the proteinogenic amino-acid of lowest molecular weight, harboring a hydrogen
atom as a side-chain. In addition to being a building-block for proteins, glycine is also required for
multiple metabolic pathways, such as glutathione synthesis and regulation of one-carbon metabolism.
Although generally viewed as a non-essential amino-acid, because it can be endogenously synthesized
to a certain extent, glycine has also been suggested as a conditionally essential amino acid. In metabolic
disorders associated with obesity, type 2 diabetes (T2DM), and non-alcoholic fatty liver disease
(NAFLDs), lower circulating glycine levels have been consistently observed, and clinical studies
suggest the existence of beneficial e ects induced by glycine supplementation. The present review
aims at synthesizing the recent advances in glycine metabolism, pinpointing its main metabolic
pathways, identifying the causes leading to glycine deficiency—especially in obesity and associated
metabolic disorders—and evaluating the potential benefits of increasing glycine availability to curb
the progression of obesity and obesity-related metabolic disturbances. This study focuses on the
importance of diet, gut microbiota, and liver metabolism in determining glycine availability in obesity
and associated metabolic disorders.
Keywords: amino acid metabolism; gut–liver axis; pathophysiology of metabolic disorders;
nutritional
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