Glycine, obesity and metabolic disease: what the evidence shows
What it found
People with obesity, type 2 diabetes and fatty liver disease tend to have lower levels of glycine in their blood than healthy people.
Some small studies in people suggest glycine supplements may improve insulin response and glucose tolerance.
What they found
Studies in people
Lower glycine in metabolic disease
People with obesity, type 2 diabetes and fatty liver disease consistently have lower levels of glycine in their blood than healthy people. One analysis found glycine was 11% lower in obesity and 15% lower in type 2 diabetes.
Glycine and insulin sensitivity
Among all amino acids measured, glycine had the strongest link to how well insulin works in 399 non-diabetic people. Higher glycine went with better insulin sensitivity.
Glycine supplements in people
A dose of 5 g of glycine per day improved insulin response and glucose tolerance in short-term studies. A longer study giving 0.1 g per kg per day for 14 days alongside N-acetylcysteine improved insulin sensitivity in older patients with HIV.
Betaine supplement trial
A randomised trial of betaine supplements in people with obesity and pre-diabetes found no major effect on blood sugar control or liver fat. Betaine is a precursor that the body can turn into glycine.
Animal and lab studies
Gut bacteria use glycine
In young pigs, about 30% of dietary glycine was used or broken down in the small intestine by gut bacteria before it could reach the rest of the body. In people with type 2 diabetes not taking metformin, gut bacteria had more genes for breaking down glycine.
Studies in people and animals
Glycine and glutathione
Glutathione, an antioxidant, was 60% lower in red blood cells of people with type 2 diabetes compared to controls. Glycine supplements raised glutathione levels in some animal models and in people.
What the authors conclude
“However, it is still unclear whether the decline in glycine levels is causatively involved in the pathogenesis of metabolic disorders, particularly glucose intolerance, insulin resistance, and T2DM.”
Also in their conclusions
- They say glycine is now recognised as a relevant blood marker for metabolic diseases linked to obesity and is a promising amino acid for improving metabolic health.
- They note it is still unclear whether the drop in glycine levels actually causes these metabolic disorders.
- They call for long-term intervention studies and dose-finding studies to confirm any benefit of glycine supplements.
How it was done
The authors wanted to pull together recent findings on how glycine is made and used in the body, why levels fall in obesity and related conditions, and whether raising glycine intake could help slow these conditions.
They reviewed published studies on glycine metabolism, including dietary surveys, blood measurements in people, animal experiments and some small supplement trials. They looked at how diet, gut bacteria and liver metabolism affect glycine levels.
What it can’t tell you
- Most of the evidence linking low glycine to metabolic disease comes from studies that follow people over time, which can show a link but not prove that low glycine causes the disease.
- Many of the supplement studies were short or small, so they cannot show what happens over years.
- Animal and lab studies cannot show what happens in people.
Who paid
- Conflicts
- The authors do not have any conflict of interest to declare.
- Authors work at
- Université de Lyon, France
The paper
- Title
- Glycine Metabolism and Its Alterations in Obesity and Metabolic Diseases
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Alves A, Bassot A, Bulteau AL, Pirola L, Morio B (2019). Glycine Metabolism and Its Alterations in Obesity and Metabolic Diseases. Nutrients. doi:10.3390/nu11061356Free full textPubMed 31208147DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error