The Study
Role of insulin in the regulation of human skeletal muscle protein synthesis and breakdown: a systematic review and meta-analysis
This study looked at lots of small experiments where scientists gave people extra insulin and measured what happened to their muscles. It found that insulin helps stop muscles from breaking down, but only helps build muscle if you also eat enough protein. It doesn't prove that taking insulin makes your muscles bigger over time.
Analysis score
Maximum 85 for a systematic review with meta-analysis.
Where the score came from
Insulin doesn't make your muscles grow by itself, but it stops them from breaking down — like a bodyguard for your muscle proteins.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 544 / 100
Quality score
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
Key takeaways
Summary
Based on the study abstract and findings.
- 1This means even small insulin increases (like after eating) are enough to protect your muscles from breaking down — but to build muscle, you need protein too.
- 2In diabetes, this protective system doesn't work right.
- 3Insulin reduces muscle breakdown by 15.46 units and improves net muscle balance by 20.09 units.
- 4It only builds muscle when amino acids are also increased (+13.44 units).
- 5In diabetics, insulin actually reduces muscle building by 6.67 units.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Diabetologia
Year
2015
Authors
H. Abdulla, Kenneth Smith, P. Atherton, I. Idris
Related Content
Claims (6)
Persistently high insulin levels lead to impaired metabolism and increased fat storage, while short-term increases in insulin stimulate the building of muscle protein.
Insulin does not increase muscle protein synthesis in healthy people unless more amino acids are delivered to the muscles. When amino acid delivery increases, insulin raises muscle protein synthesis by 13.44 nmol per 100 ml of leg volume per minute.
In healthy humans, insulin raises the net balance of muscle protein by 20.09 nmol per 100 ml of leg volume per minute by reducing the rate at which muscle protein is broken down, not by increasing the rate of muscle protein production.
In healthy humans, insulin directly lowers the rate of muscle protein breakdown by 15.46 nmol per 100 ml of leg volume per minute, regardless of amino acid levels, showing its main effect on muscle is to prevent breakdown rather than to build new protein.
In people with diabetes, insulin decreases the rate of muscle protein synthesis by 6.67 nmol per 100 ml of leg volume per minute, even when amino acids are supplied normally, showing that insulin’s ability to stimulate muscle growth is impaired in diabetic muscle.
At insulin concentrations around 104.2 pmol/L, muscle protein breakdown reaches its lowest rate, and higher insulin levels do not suppress it further.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.