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Research · Supplements

CLA

Meta-analyses found fat loss of about 0.1 kg a week at 3.2 g a day and about 0.4 to 1.3 kg overall, with body weight 0.4 to 0.7 kg lower than placebo. Higher-quality trials showed no fat mass change. In obese men, the trans-10 cis-12 isomer raised insulin resistance 19% and CRP 110%. Pooled trials found CRP higher with CLA.

Add to Bio HackChecked 2026-11-13
Status
Dietary supplement in the US.
Also called
conjugated linoleic acid, Tonalin, Clarinol, trans-10 cis-12 CLA, t10c12 CLA, cis-9 trans-11 CLA, rumenic acid, CLA softgels
Taken for
fat loss, weight loss, belly fat, lean muscle, toning, body composition

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help3

Reported risks3

What people take it for, and what was found

Shown to help3

Strong

Body weight

Shown to lower body weight by about 0.35 to 0.7 kg more than placebo in adults, a change that may not be clinically important.

The numbers and sources
Effect
In trials of 6 months or more, weight loss was 0.70 kg greater than placebo (95% CI -1.09 to -0.32) [2]. Across 70 RCTs, body weight was 0.35 kg lower (95% CI -0.54 to -0.15) and BMI 0.15 kg/m² lower [3].
Population
Overweight and obese adults [2]; adults [3].
Sources
[2], [3]
Caveats
The authors of [3] wrote that the weight change may not reach clinical importance.
Moderate

Lean mass

Shown to raise fat-free mass by about 0.3 kg in adults, under 1% of fat-free mass.

The numbers and sources
Effect
In the same 18 trials pooled for fat loss, fat-free mass rose 0.3 kg during CLA treatment, with no effect of dose or duration [4]. In 70 RCTs, fat-free mass rose 0.27 kg (95% CI 0.09 to 0.45) [3].
Population
Adults in RCTs [3][4].
Sources
[3], [4]
Caveats
The change was under 1% of fat-free mass [4].
Moderate

CLA combined with exercise

Shown to lower body fat and insulin resistance more than exercise alone, mainly in women, people with a BMI of 25 or more and after 4 weeks.

The numbers and sources
Effect
In 20 trials of CLA plus exercise against exercise alone, body fat fell more (SMD -0.42, 95% CI -0.70 to -0.14, I² 65%) and insulin resistance fell more (SMD -0.25, 95% CI -0.44 to -0.06). Body weight, exercise performance and blood lipids did not differ [5].
Population
18 RCTs and 2 crossover trials [5].
Sources
[5]
Caveats
Effects were seen mainly in subgroups with BMI of 25 or more, women and interventions longer than 4 weeks [5].

Mixed results1

Moderate

Fat mass

Mixed results: pooled trials found about 0.4 to 1.3 kg more fat loss than placebo in adults, while the high-quality subgroup showed no change.

The numbers and sources
Effect
Across 18 placebo-controlled trials, CLA at a median 3.2 g a day reduced fat mass by 0.09 kg a week more than placebo, with the effect linear up to 6 months [1]. In 7 trials lasting at least 6 months, fat loss was 1.33 kg greater than placebo (95% CI -1.79 to -0.86, I² 54%) [2]. In 70 RCTs with 4,159 participants, fat mass was 0.44 kg lower (95% CI -0.66 to -0.23) and body fat 0.77 percentage points lower, but the high-quality subgroup showed no change in fat mass or body fat percentage [3].
Population
Adults in RCTs [1][3]; overweight and obese adults [2].
Sources
[1], [2], [3]
Caveats
Four of the 7 long-term trials had serious reporting flaws, and the authors called the effect's clinical relevance uncertain [2]. The pooled estimates shrink as trial quality rises [3].

Doses studied

The fat mass meta-analysis adjusted results to a median 3.2 g of CLA a day [1]. Long-term trials ran 6 months or more [2]. The insulin resistance trial in obese men used 3.4 g a day of a CLA isomer mixture or of purified trans-10 cis-12 CLA for 12 weeks [6].

Risks

Reported risks3

LimitedStudied in menHow often is not known

Insulin resistance with the trans-10 cis-12 isomer

One trial found the purified trans-10 cis-12 isomer raised insulin resistance by 19% in 60 obese men. The commercial mixture did not change glucose metabolism.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In 60 abdominally obese men given 3.4 g a day for 12 weeks, purified trans-10 cis-12 CLA raised insulin resistance by 19% and blood glucose by 4%, and lowered HDL cholesterol by 4%, compared with placebo. The commercial isomer mixture did not change glucose metabolism and lowered HDL by 2% [6].
Population
60 men with signs of the metabolic syndrome, measured by euglycemic clamp [6].
Sources
[6]
Caveats
One trial. Pooled trials of CLA with exercise found insulin resistance lower, not higher [5].
ModerateHow often is not known

Inflammation and oxidative stress markers

Shown to raise CRP in adults across 14 studies. Sources disagree on oxidative stress, with one marker rising and another falling.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Across 14 studies, CLA raised serum CRP by 0.63 mg/dL, the unit as the review's abstract prints it (95% CI 0.13 to 1.13, I² 52.3%), independent of dose or duration [7]. In the 12-week trial in obese men, trans-10 cis-12 CLA raised the lipid peroxidation marker 8-iso-PGF2α by 578% and CRP by 110% compared with placebo [8]. A separate pooled analysis of 22 RCTs found malondialdehyde, another oxidative stress marker, lower with CLA [9].
Population
Adults in prospective studies [7]; 60 men with metabolic syndrome randomized to trans-10 cis-12 CLA, a CLA mixture or placebo, the same design as [6] [8]; adults in RCTs [9].
Sources
[7], [8], [9]
Caveats
The size of the CRP rise is uncertain. The abstract of [7] gives it in mg/dL, and 0.63 mg/dL is 6.3 mg/L, a large change for a pooled result. The full text could not be read to confirm the unit, so the direction is reported here and the size is not relied on. Sources disagree on oxidative stress. The isoprostane rise [8] and the malondialdehyde fall [9] used different markers and mostly different products.
ModerateHow often is not known

Digestive side effects

Long-term trials reported constipation, diarrhea and soft stools. Adverse events were about as common with CLA plus exercise as with exercise alone.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Long-term trials reported constipation, diarrhea and soft stools [2]. In trials of CLA with exercise, adverse events did not differ from exercise alone (risk ratio 1.32, 95% CI 0.94 to 1.84) [5].
Population
RCTs [2][5].
Sources
[2], [5]
Caveats
Event counts are not given in the abstract of [2].

Checked, no increase found1

Moderate

Liver enzymes

ALT and AST did not change with CLA against control across 22 trials.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In 22 RCTs, ALT and AST did not change with CLA compared with control [9].
Population
Adults in RCTs [9].
Sources
[9]
Caveats
Effect sizes are not given in the abstract.

Claims tested and not found

  1. That CLA reduces fat mass in high-quality trials. The high-quality subgroup of 70 RCTs showed no change in fat mass or body fat percentage [3].
  2. That CLA improves exercise performance. Performance did not differ between CLA plus exercise and exercise alone [5].
  3. That CLA added to exercise lowers body weight. Body weight did not differ from exercise alone [5].

Sources

  1. Whigham LD, Watras AC, Schoeller DA. Efficacy of conjugated linoleic acid for reducing fat mass: a meta-analysis in humans. American Journal of Clinical Nutrition. 2007. https://doi.org/10.1093/ajcn/85.5.1203
  2. Onakpoya IJ, Posadzki PP, Watson LK, et al. 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. European Journal of Nutrition. 2012. https://doi.org/10.1007/s00394-011-0253-9
  3. Asbaghi O, Shimi G, Hosseini Oskouie F, et al. The effects of conjugated linoleic acid supplementation on anthropometrics and body composition indices in adults: a systematic review and dose-response meta-analysis. British Journal of Nutrition. 2024. https://doi.org/10.1017/s0007114523001861
  4. Schoeller DA, Watras AC, Whigham LD. A meta-analysis of the effects of conjugated linoleic acid on fat-free mass in humans. Applied Physiology, Nutrition, and Metabolism. 2009. https://doi.org/10.1139/h09-080
  5. Liang CW, Cheng HY, Lee YH, et al. Effects of conjugated linoleic acid and exercise on body composition and obesity: a systematic review and meta-analysis. Nutrition Reviews. 2023. https://doi.org/10.1093/nutrit/nuac060
  6. Risérus U, Arner P, Brismar K, et al. Treatment With Dietary trans10cis12 Conjugated Linoleic Acid Causes Isomer-Specific Insulin Resistance in Obese Men With the Metabolic Syndrome. Diabetes Care. 2002. https://doi.org/10.2337/diacare.25.9.1516
  7. Mazidi M, Karimi E, Rezaie P, et al. Effects of conjugated linoleic acid supplementation on serum C-reactive protein: A systematic review and meta-analysis of randomized controlled trials. Cardiovascular Therapeutics. 2017. https://doi.org/10.1111/1755-5922.12275
  8. Risérus U, Basu S, Jovinge S, et al. Supplementation With Conjugated Linoleic Acid Causes Isomer-Dependent Oxidative Stress and Elevated C-Reactive Protein: A Potential Link to Fatty Acid-Induced Insulin Resistance. Circulation. 2002. https://doi.org/10.1161/01.cir.0000033589.15413.48
  9. Haghighat N, Shimi G, Shiraseb F, et al. The effects of conjugated linoleic acid supplementation on liver function enzymes and malondialdehyde in adults: A GRADE-assessed systematic review and dose-response meta-analysis. Pharmacological Research. 2022. https://doi.org/10.1016/j.phrs.2022.106518

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