We use essential cookies (authentication, your saved goals/stack) by default. With your permission we’ll also enable privacy-respecting analytics (Vercel Web Analytics, anonymous load-time metrics) and error-replay diagnostics (Sentry — DOM snapshots only when an error fires) so we can fix bugs faster. Learn more about cookies
Conjugated Linoleic Acid
A group of fatty-acid isomers heavily marketed as a fat-loss aid. The honest picture: meta-analyses of human trials show only a small, inconsistent reduction in fat mass that the authors themselves call clinically uncertain — and the active t10c12 isomer has actually WORSENED insulin sensitivity and lowered HDL in obese men.
What the evidence says
Most CLA studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from high-quality meta-analyses and randomised trials published 2000–2026 with a typical study size of 1,476 participants.
Based on 142 studies · 21 meta-analyses · 115 RCTs · 5,700 total participants
Confidence
High confidenceBy outcome
Human meta-analyses find only a small, clinically-uncertain fat-mass reduction with no reliable weight loss, while the active t10c12 isomer worsened insulin resistance and HDL — so the score stays low and emerging.
145 rigorous studies
121 randomized trials · 21 meta-analyses · 3 systematic reviews
Our evidence rating for CLA is accountable to this entire body of rigorous research indexed in PubMed — not a hand-picked subset.
PubMed · as of Jul 2026
65 trials ongoing or recruiting · 374 completed on ClinicalTrials.gov
71 of the completed trials have posted results
Registered trials show research momentum for CLA, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Sep 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for CLA meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Not authorised by EFSA
“CLA (conjugated linoleic acid) CLA can support lean body mass”
“CLA (conjugated linoleic acid) CLA may protect against free radicals”
“CLA or conjugated linoleic acid Strong plant antioxidant. Antioxidant”
“Conjugated linoleic acid (CLA) Contributes to healthy blood glucose level”
“Conjugated linoleic acid (CLA) Helps to reduce muscle protein 'loss during a diet”
“Conjugated linoleic acid (CLA) Support of (HepB) vaccine response/Helps respiratory comfort in asthma”
“Conjugated linoleic acid (CLA) Aids slimming by reducing body fat and preserving lean muscle Helps to reduce muscle protein loss during a diet”
“CLA (acido linoleico coniugato) Con acido linoleico coniugato che AIUTA A DIMAGRIRE Clarification provided Conjugated linoleic acid can support lean body mass”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Conjugated linoleic acid (CLA) is a family of positional and geometric isomers of linoleic acid, sold as a body-composition supplement on the strength of dramatic fat-loss effects seen in mice. In humans the story is far weaker.
The two most-cited human meta-analyses (Whigham 2007; Onakpoya 2012) find at most a small fat-mass reduction (~1.3 kg over many months) that the authors describe as of 'uncertain' clinical relevance, with serious methodological flaws in several included trials and no convincing effect on body weight.
More concerning, the purified trans-10,cis-12 isomer — the one thought to drive fat loss — increased insulin resistance by ~19% and lowered HDL cholesterol in a controlled trial of abdominally obese men (Risérus 2002).
So CLA is a case where the marketing outruns the evidence, and where the 'active' isomer carries a real metabolic downside. We score it low and emerging.
In rodents the t10c12 isomer reduces fat storage and increases fat oxidation; these effects are far smaller and less consistent in humans.
Proposed modulation of adipocyte differentiation and lipid-handling enzymes — mechanistic, and the same pathway implicated in the adverse insulin/HDL signals.
How CLA works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Avoid — t10c12 CLA worsened insulin sensitivity in obese men with metabolic syndrome.
Not established as safe — avoid.
CLA (especially the t10c12 isomer) has worsened insulin sensitivity and raised glycemia in trials — may oppose glucose control.
CLA has lowered HDL cholesterol in trials — an unfavorable lipid shift.
Tip: Take with food; discontinue if persistent
Tip: Monitor lipids; avoid in those with low HDL
Tip: Avoid isolated t10c12; caution in metabolic syndrome
CLA has an evidence score of 3/10 — emerging evidence based on 118 indexed studies, including 2 meta-analyses. A group of fatty-acid isomers heavily marketed as a fat-loss aid. The honest picture: meta-analyses of human trials show only a small, inconsistent reduction in fat mass that the authors themselves call clinically uncertain — and the active t10c12 isomer has actually WORSENED insulin sensitivity and lowered HDL in obese men. Representative study: PMID 21990002.
The commonly studied dose of CLA is 3.2-3.4g daily of CLA isomer mix (the dose used in most trials; benefit remains small/uncertain). Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take CLA is with meals. Take it with food. Fat-soluble; taken with meals to reduce GI upset.
CLA should be used with caution — talk to a healthcare provider before taking it. The most commonly reported side effects are GI upset (constipation, diarrhea, soft stools), reduced HDL cholesterol, increased insulin resistance (t10c12 isomer). Use caution if any of these apply to you: Metabolic syndrome / insulin resistance / type 2 diabetes (t10c12 worsened insulin sensitivity); Pregnancy/breastfeeding (not established as safe).
Caffeine
Likely helpsBlocks adenosine receptors to boost alertness, reaction time, and endurance — one of the most proven ergogenic aids.
Berberine
Likely helpsActivates AMPK to regulate blood sugar, improve insulin sensitivity, and support lipid metabolism — comparable to metformin in some trials.
Epicatechin
Probably helpsDark chocolate flavanol with consistent human evidence for improved endothelial function and modest blood pressure reduction. Muscle-building claims are not supported in humans.
Beta-Ecdysterone
Mostly mechanism / observationalPhytoecdysteroid that activates the PI3K/Akt pathway; studied for muscle protein synthesis and strength. Non-steroidal, though human strength evidence is limited.
Explore: Best supplements for Vitality & LongevityBest supplements for Athletic Performance
Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 142 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
Tap node to isolate • Pinch to zoom • Tap edge for research