Glycine supplements in severe obesity: metabolic and liver markers
What it found
In 19 people with severe obesity, two weeks of glycine supplements raised blood glycine and changed several metabolic and liver markers.
Body weight, blood sugar and insulin did not change.
What they found
Studies in people
Glycine levels rose
Plasma glycine increased by 49.2 micromol/L, about 35%, reaching levels similar to healthy normal-weight people. Serine and cysteine also rose, while tryptophan fell slightly.
Detoxification pathway
Urine levels of four acylglycines (isobutyrylglycine, tigylglycine, isovalerylglycine, hexanoylglycine) increased significantly. This suggests the glycine conjugation pathway that clears potentially toxic metabolites was working harder.
Liver markers improved
Plasma triglyceride and the liver enzymes alanine transaminase and aspartate transaminase fell significantly. The glutamate-serine-glycine index, a marker linked to metabolic dysfunction-associated liver disease, also improved.
No change in weight or blood sugar
Body weight, body composition, blood pressure, cholesterol, fasting glucose, insulin, and measures of insulin resistance did not change. Energy expenditure and fuel oxidation rates also stayed the same.
Antioxidant and one-carbon effects
Red blood cell glutathione and plasma malondialdehyde did not change. However, plasma folate and homocysteine rose, which the authors interpret as increased one-carbon cycle activity.
What the authors conclude
“In conclusion, we found that dietary glycine supplements corrected obesity-associated glycine deficiency, increased urine acylglycine excretion, and plasma metabolites associated with one-carbon metabolism.”
Also in their conclusions
- They conclude that dietary glycine supplements corrected obesity-associated glycine deficiency and enhanced the glycine conjugation detoxification reaction and one-carbon cycle flux.
- They say the improvements in liver markers suggest glycine supplements should be investigated as a potential novel treatment for MASLD.
- They advise that future randomized controlled trials with larger sample sizes and longer durations are needed to confirm clinical efficacy and safety.
How it was done
People with severe obesity tend to have low glycine, which may impair detoxification, antioxidant defences and one-carbon metabolism. The authors wanted to see whether glycine supplements could correct this and improve related metabolic pathways.
19 adults with severe obesity took oral glycine at 100 mg/kg/day for two weeks. Blood and urine were collected before and after to measure amino acids, acylglycines, liver markers, glutathione, and other metabolic measures.
What it can’t tell you
- This was a small exploratory study without a control group, so it cannot prove that glycine supplements caused the changes seen.
- The study did not include liver imaging or biopsy, so it cannot confirm effects on liver tissue itself.
- The two-week duration means longer-term effects and safety, including on homocysteine, remain unknown.
Who paid
- Funding
- Funded by Khoo Mentored Research Award (from the PubMed record).
- Conflicts
- Declarations. Competing interests: The authors declare no competing interests.
- Authors work at
- Singapore General Hospital, Singapore; Duke-NUS Medical School, Singapore; USDA/ARS Children's Nutrition Research Centre, USA
The paper
- Title
- Metabolic impact of dietary glycine supplementation in individuals with severe obesity
- Type
- Clinical trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Tan HC, Hsu JW, Tai ES, et al (2025). Metabolic impact of dietary glycine supplementation in individuals with severe obesity. Scientific reports. doi:10.1038/s41598-025-20511-xFree full textPubMed 41107432DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error