Conjugated Linoleic Acid (CLA)
Summary
CLA is sold for fat loss. Across 70 trials it lowered body weight by about 0.35 kg and fat mass by about 0.44 kg, but high-quality trials showed no fat loss (grade C). One isomer, t10,c12, raised insulin resistance by 19% in obese men. EFSA found CLA safe for up to six months but not established beyond that or in type 2 diabetes.
Key facts
- A mix of fatty acid isomers found mainly in dairy and beef; supplements usually contain c9,t11 and t10,c12 in equal parts[1][2]
- Body fat (small effect, C); lean mass (small increase, C); insulin sensitivity (no benefit; t10,c12 worsened it)[6][8][9][10]
- EFSA: safe for up to six months at 3–3.5 g/day; safety beyond six months and in type 2 diabetes not established; body-fat claim rejected in 2015[2][3]
- The 1-year and 6-month trials were run by Scandinavian Clinical Research AS, a contract research firm; the 12-month safety trial tested the branded product Clarinol[8][10][13]
- 6 graded human outcomes on this page
- October 10, 2026
How it works
ProposedIn animal and laboratory studies, CLA increases fat breakdown and fatty acid burning in muscle, reduces fat storage and promotes fat-cell death. The t10,c12 isomer drives most of these effects and also the insulin-resistance signal.[1][9]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Body fat | Grade C | Improved | Meta-analysis of 70 trials · n = 4,159 · 2024 | 3 rows |
| Insulin sensitivity | Grade C | No effect | RCT · n = 118 · 2007 | 2 rows |
| Lean mass | Grade D | Improved | RCT · n = 66 · 2020 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Body weight and fat mass | Improved | Grade C | Meta-analysis · n = 4,159 · 2024 Adults in 70 randomized trials Form: CLA supplements (mostly isomer mixtures) · Dose: Varied across trials · Duration: Varied across trials CLA lowered body weight by 0.35 kg, fat mass by 0.44 kg and body fat by 0.77 percentage points versus placebo; in high-quality trials it did not change fat mass or body fat percentage. | 37671495 (opens PubMed)Source [6] |
| Body fat mass | Improved | Grade C | RCT · n = 180 · 2004 Healthy adults with overweight (BMI 25–30) Form: CLA as free fatty acid or triglyceride (isomer mixture) · Dose: About 3.4–3.6 g CLA daily (per the NIH ODS summary) · Duration: 1 year Body fat mass was 6.9–8.7% lower than placebo; LDL rose with the free fatty acid form, HDL fell with the triglyceride form, and lipoprotein(a) rose in both CLA groups. | 15159244 (opens PubMed)Source [8] |
| Insulin sensitivity (clamp test) | No effect | Grade C | RCT · n = 118 · 2007 Adults with overweight or obesity Form: CLA isomer mixture (Clarinol) · Dose: Dose not stated in the abstract · Duration: 6 months CLA did not change insulin sensitivity measured by clamp in the 49-person clamp subgroup (41 completed both clamps), or fasting measures of insulin resistance, compared with olive oil placebo. | 17031391 (opens PubMed)Source [10] |
| Insulin resistance (an adverse effect) | Worsened | Grade C | RCT · n = 60 · 2002 Abdominally obese men with metabolic syndrome Form: Purified t10,c12-CLA or CLA isomer mixture · Dose: 3.4 g daily · Duration: 12 weeks Purified t10,c12-CLA raised insulin resistance by 19% and blood glucose by 4% and lowered HDL by 4% versus placebo; the isomer mixture did not change glucose metabolism or body composition but lowered HDL by 2%. | 12196420 (opens PubMed)Source [9] |
| Muscle mass | Improved | Grade D | RCT · n = 66 · 2020 Chinese adults aged 18–45 with high body fat Form: CLA capsules · Dose: 3.2 g daily · Duration: 12 weeks The authors concluded CLA may help preserve muscle mass, especially in the trunk, compared with sunflower oil placebo. | 32684362 (opens PubMed)Source [12] |
| Body composition and blood lipids | No effect | Grade D | Crossover RCT · n = 27 · 2011 Men aged 18–60 with overweight and borderline high LDL cholesterol Form: CLA isomer mixture (Clarinol G-80) or c9,t11-CLA · Dose: 3.5 g daily · Duration: 8 weeks per phase Neither CLA preparation changed body composition, lipid profile or safety markers compared with safflower oil. | 21593349 (opens PubMed)Source [11] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| 50:50 isomer mixture (c9,t11 and t10,c12), e.g. Tonalin, Clarinol | Varies[1][2][8] | About 80% CLA isomers in the branded oils; no human absorption figures in our sources.[2] | Mostly digestive upsets (constipation, diarrhea, loose stools, nausea); EFSA considered it safe for up to six months.[1][2][5] | Most body-composition trials at 3.2–3.6 g/day |
| Purified t10,c12-CLA | Varies[9] | No absorption data in our sources.[9] | Raised insulin resistance and blood glucose and lowered HDL in obese men.[9] | Insulin-sensitivity research; not a typical retail form |
| c9,t11-CLA (the main form in dairy and beef) | Varies[1][11] | No absorption data in our sources.[11] | No change in safety markers over 8 weeks at 3.5 g/day.[11] | Food sources and a few single-isomer trials |
Studied doses
Doses studied in human trials ranged from 3.2 to 3.6 g/day for 8 weeks to 1 year in body-composition trials, up to 6 g/day in a 12-month safety trial. Pooled analyses put the typical dose at about 3.2 g/day.[4][8][12][13]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- Diabetes medicinesRCTThe t10,c12 isomer raised insulin resistance and glucose in obese men, and EFSA says CLA safety in type 2 diabetes has not been established.[9][2]
- Cholesterol-lowering medicinesRCTCLA raised lipoprotein(a) and shifted LDL or HDL in a 1-year trial, though pooled trials in people at cardiovascular risk found no effect on lipids.[8][7]
Who should be careful
- Type 2 diabetes or insulin resistance
- EFSA says CLA safety in type 2 diabetes is not established, and purified t10,c12-CLA worsened insulin resistance in men with metabolic syndrome.[2][9]
- Use beyond six months
- EFSA found CLA safe at the proposed doses for up to six months; longer use has not been shown to be safe.[2]
- Breastfeeding
- The NIH ODS notes CLA might lower breast-milk fat, though more research is needed.[1]
- Liver concerns
- Three case reports linked CLA products to hepatitis, though contamination could not be ruled out.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Safety
CLA is mostly well tolerated, but regulators flag open questions about long-term use and metabolic effects.
- Insulin and glucose
- Purified t10,c12-CLA raised insulin resistance by 19% in obese men; the isomer mixture did not change insulin sensitivity over 6 months in another trial.[9][10]
- Blood lipids and inflammation
- A 1-year trial found higher lipoprotein(a); EFSA noted rises in lipid peroxidation and inflammation markers that could mean vascular harm in the longer term.[8][3]
- Digestive effects
- Constipation, diarrhea and soft stools were the main side effects in pooled trials.[5][1]
- 12-month safety trial
- In a trial of 6 g/day Clarinol, laboratory tests showed no adverse effects and side effects were less common than with placebo.[13]
How to read the label
- Label dose vs clinical doseMost trials used 3.2–3.6 g/day of CLA isomers; check that the label states isomer content, not just oil weight.[4][8][2]
- Isomer ratioRetail CLA is usually a 50:50 mix of c9,t11 and t10,c12; the t10,c12 isomer carries the insulin-resistance signal.[1][9]
- ClaimsEFSA rejected a "reduction in body fat mass" claim for Clarinol and Tonalin in 2015.[3]
Cost per studied dose, without the sales pitch
Compare any product you already have by the amount it delivers, not by capsule count or front-of-pack weight.
Cost per studied dose
Enter the price, servings and the amount per serving from your label.
Frequently asked questions
Does CLA help you lose fat?
Only slightly. Pooled trials found about 0.44 kg less fat mass, and high-quality trials found no fat loss.[6]
Is CLA safe?
EFSA judged CLA safe at 3–3.5 g/day for up to six months; safety for longer use and in type 2 diabetes is not established.[2]
Does CLA affect blood sugar?
The purified t10,c12 isomer raised insulin resistance by 19% in obese men; a mixed-isomer product did not change insulin sensitivity over 6 months.[9][10]
Does CLA build muscle?
Some trials found small gains or preservation of lean mass, such as a 12-week trial of 3.2 g/day in Chinese adults.[6][12]
What foods contain CLA?
CLA is found mainly in dairy products and beef, mostly as the c9,t11 isomer.[1]
Sources
- [1]Dietary Supplements for Weight Loss: Fact Sheet for Health Professionals (updated May 18, 2022). NIH Office of Dietary Supplements, 2022. fact-sheet
- [2]Statement on the safety of the "conjugated linoleic acid (CLA) rich oils" Clarinol and Tonalin TG 80 as Novel Food ingredients (EFSA Journal 2012;10(5):2700). European Food Safety Authority (EFSA) NDA Panel, 2012. guideline
- [3]Scientific Opinion on the substantiation of a health claim related to an equimolar mixture of the CLA isomers c9,t11 and t10,c12 (Clarinol and Tonalin) and "contributes to a reduction in body fat mass" (EFSA Journal 2015;13(1):3953). European Food Safety Authority (EFSA) NDA Panel, 2015. guideline
- [4]Efficacy of conjugated linoleic acid for reducing fat mass: a meta-analysis in humans.. Am J Clin Nutr, 2007. meta-analysis
- [5]The efficacy of long-term conjugated linoleic acid (CLA) supplementation on body composition in overweight and obese individuals: a systematic review and meta-analysis of randomized clinical trials.. Eur J Nutr, 2012. meta-analysis
- [6]The effects of conjugated linoleic acid supplementation on anthropometrics and body composition indices in adults: a systematic review and dose-response meta-analysis.. Br J Nutr, 2024. meta-analysis
- [7]The effects of conjugated linoleic acid supplementation on cardiovascular risk factors in patients at risk of cardiovascular disease: A GRADE-assessed systematic review and dose-response meta-analysis.. Br J Nutr, 2024. meta-analysis
- [8]Conjugated linoleic acid supplementation for 1 y reduces body fat mass in healthy overweight humans.. Am J Clin Nutr, 2004. RCT
- [9]Treatment with dietary trans10cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome.. Diabetes Care, 2002. RCT
- [10]The effect of 6 months supplementation with conjugated linoleic acid on insulin resistance in overweight and obese.. Int J Obes (Lond), 2007. RCT
- [11]Conjugated linoleic acid supplementation for 8 weeks does not affect body composition, lipid profile, or safety biomarkers in overweight, hyperlipidemic men.. J Nutr, 2011. crossover-RCT
- [12]Conjugated linoleic acid supplements preserve muscle in high-body-fat adults: A double-blind, randomized, placebo trial.. Nutr Metab Cardiovasc Dis, 2020. RCT
- [13]Safety profile of conjugated linoleic acid in a 12-month trial in obese humans.. Food Chem Toxicol, 2004. RCT
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: every evidence row re-read against its PubMed abstract; the 1-year trial dose is taken from the NIH ODS weight-loss fact sheet because the abstract omits it. Official sources opened before citing: NIH ODS Dietary Supplements for Weight Loss (updated May 18, 2022), EFSA 2012 statement on Clarinol and Tonalin TG 80 safety, EFSA 2015 opinion rejecting the body-fat claim. Industry ties: 1-year and 6-month trials by Scandinavian Clinical Research AS; the 12-month safety trial tested Clarinol; the 2015 EFSA claim was filed by BASF and Stepan Lipid Nutrition. Meta-analyses without a participant total (2007, 2012, 2024 cardiovascular) are cited in insights and FAQ only. Retraction, expression-of-concern, erratum and withdrawn checks on all 10 PMIDs: none flagged. Page set indexable. Independent browser review (4 parallel reviewers, every evidence row checked against its abstract and official sources on the Vercel preview) found issues that were fixed: evidence direction now follows the site convention (up = improved, down = worsened), plus wording and disclosure corrections listed in the batch-14 PR review comment.