Conjugated linoleic acid (CLA)Fat

• Fat massPossibly helps

  The two big poolings reach opposite conclusions, and the newer one is less flattering.
  
  A 2007 meta-analysis of 18 human RCTs found CLA at a median 3.2 g/day produced a modest reduction in fat mass against placebo [2].
  
  A 2023 systematic review and dose-response meta-analysis found small but statistically significant improvements in body-composition markers — while noting that the high-quality studies failed to show a fat-lowering effect [4]. Its authors judged any real effect too small to be clinically important.
  
  Other reviews describe the picture across trials as simply inconsistent: some show reduced fat mass, some show none [6]. ^[4]

• Lean and muscle massPossibly helps

  A 2020 double-blind, randomised, placebo-controlled trial in Chinese adults with elevated body-fat percentage used 3.2 g/day for 12 weeks [5].
  
  Trunk muscle mass rose against placebo — with no significant between-group difference in fat mass change in that same trial [5].
  
  So the muscle result and the fat result did not arrive together. Other reviews report trials showing increased or preserved lean mass, and others showing nothing [3]. ^[5]

• c9,t11 — the isomer nature makesThis is what you get from grass-fed butter or beef, at milligram rather than gram scale .

  Elemental content

  Roughly 80–90% of the CLA in ruminant meat and dairy, but only about 40–45% of a supplement

  Absorption

  In animal models it is associated with neutral-to-improved lipid metabolism, and in some studies better insulin sensitivity [12].
  
  In an ob/ob mouse study it did not significantly raise liver lipid weight [20].

  Best for

  This is what you get from grass-fed butter or beef, at milligram rather than gram scale [8].

• t10,c12 — the isomer supplements are loaded withNothing this page recommends. Its risk profile is covered in the interactions section below .

  Elemental content

  About 3–5% of natural CLA, but 40–45% of a typical commercial supplement

  Absorption

  This is the isomer more consistently driving fat-mass loss in research [3].
  
  It is also the one linked to insulin resistance and to adverse glucose and lipid changes in animal work [12].
  
  The fat-loss effect and the metabolic-risk signal appear to travel together in the same molecule.

  Best for

  Nothing this page recommends. Its risk profile is covered in the interactions section below [12].

• Mixed-isomer supplement — the standard productNearly every human trial used this blend, so it is what the evidence actually covers .

  Elemental content

  Roughly 40–45% c9,t11 and 40–45% t10,c12, an approximately 1:1 blend

  Absorption

  Made from safflower, sunflower, corn or soybean oil by an alkaline-catalysed reaction [3].
  
  That delivers a far higher share of t10,c12 than any diet ever would.

  Best for

  Nearly every human trial used this blend, so it is what the evidence actually covers [2].

• Free fatty acid (FFA) against triacylglycerol (TG)Taste, essentially. TG form is milder; FFA form is more astringent .

  Elemental content

  Two chemical carriers for the same isomer mix, sold interchangeably

  Absorption

  A human RCT over 12–24 months found both reduced body fat mass similarly, with no significant difference in efficacy or adverse events [17].
  
  In rats, FFA-form c9,t11 was incorporated into the liver more than TG-form, with no resulting difference in the bone outcomes measured [11].
  
  Broader animal and human evidence shows no meaningful functional split between the two forms [11].

  Best for

  Taste, essentially. TG form is milder; FFA form is more astringent [11].

• Gastrointestinal and other common effects

  A 2019 meta-analysis of body-composition trials lists nausea, stomachache, diarrhoea, bloating, headaches and skin rashes [1].
  
  A consumer drug reference names upset stomach as the single most common one [9]. Many people tolerate CLA without any of these. ^[1]

• Insulin resistance from the t10,c12 isomer

  This is the finding the weight-loss marketing does not mention.
  
  A Swedish research group gave purified t10,c12 CLA at 3.4 g/day for 12 weeks to obese men with metabolic syndrome. Insulin sensitivity worsened, and fasting glucose, insulin and C-reactive protein all rose [3].
  
  Most trials using mixed-isomer CLA — the typical commercial form — at 3–8 g/day for up to 6 months found no worsening of glucose metabolism [3]. One 6-month trial at 3.2 g/day specifically reported no adverse insulin resistance, liver function, or inflammation.
  
  The disagreement tracks the isomer, not the research group's opinion. A commercial product is roughly 40–45% t10,c12 [3]. ^[3]

• Liver fat

  The clearest liver signal is animal data, and it is isomer-specific. In a mouse study, livers of animals fed t10,c12 held about 4 times more total lipid than controls, mostly triglycerides [20].
  
  The c9,t11 isomer alone did not significantly raise liver lipid weights [20].
  
  Human trials using mixed-isomer CLA at 3–8 g/day for up to 6 months found no adverse liver-function changes [3]. Mouse liver is not human liver, and neither result cancels the other. ^[20]

• Cholesterol, in disputed directions

  The sources do not agree, so here they are separately.
  
  A 2022 meta-analysis found CLA raised triglycerides, total cholesterol and LDL — and also raised HDL [1].
  
  WebMD states CLA may lower HDL without lowering LDL [9]. Several individual trials summarised in a broader human-trials review likewise report HDL decreasing [3].
  
  That is a live disagreement about the direction of the HDL effect, not a matter of effect size. ^[1]

• No documented drug interactions is not the same as none

  A 2024 pharmacology review of weight-loss supplement interactions identified no well-established drug-drug interactions for CLA, including with statins or anticoagulants [13].
  
  A hospital-run supplement reference reports no known interactions with medicines as of its last review, while explicitly cautioning that unknown ones may exist [7].
  
  Given the isomer-specific insulin findings above, anyone on diabetes medication has a concrete reason to raise CLA with their doctor first [3]. ^[13]

• Allergy to the source oil

  Most commercial CLA is manufactured from safflower, sunflower, corn or soy oil [9].
  
  People allergic to those plants may react to the supplement because of what it was made from, not because of CLA itself [9]. ^[9]

• Pregnancy and breastfeeding

  Doctors generally do not recommend CLA supplements during pregnancy or breastfeeding, or for children, citing a lack of safety evidence [10].
  
  Whether or how supplemental CLA affects pregnancy is not known, and whether it passes into breast milk is not known either [9].
  
  One source calls CLA 'likely safe' at ordinary food amounts, while stating the evidence is insufficient at supplemental doses in either state [16]. ^[9]

• Vitamin A handling

  CLA has been shown to increase tissue levels of retinol (vitamin A) and its carrier protein RBP, by mechanisms that are not understood [13].
  
  A 2024 pharmacology review raises this as a theoretical competition for shared metabolic pathways. No clinical consequence has been documented [13]. ^[13]

CLA is essentially exclusive to ruminant animal products in nature — the meat and milk of cattle, sheep and goats [8].

Dairy is generally richer than meat. Butter runs about 6.0 mg CLA per gram of fat, mozzarella 4.9, whole homogenised milk 4.5, cheddar 3.6, against fresh ground beef at 4.3 [8].

Feed changes the number substantially. Grass-fed and pasture-raised animals yield roughly 300–500% more CLA than grain-fed ones [10].

In a controlled cattle-feeding study, adding dietary oil took beef from about 2.8 to 14 mg per gram of fat [14]. Higher-marbling Wagyu reached about 134 mg per 100 g of meat under oil-supplemented feeding, against about 25 mg per 100 g on standard feed.

So both the feed and the animal's own fat content decide what ends up on the plate [14].

Plant foods contain no meaningful amount. The vegetable-oil route only produces CLA industrially, through the alkaline reaction used to make supplements [3].

There is little direct clinical evidence on timing — most of the guidance here comes from commercial and practitioner sources rather than trials [15].

Because CLA is a fat, the standard advice is to take it with meals rather than on an empty stomach, both for absorption and to reduce nausea [15].

Published trials line up with that. Dosing is commonly split across 2–3 doses at meals rather than taken as one large hit [3].

One 16-week trial using 8 g/day had participants take 2 g with each meal plus a dose before bed [3].

No published trial establishes a required time of day. Advice to prefer mornings, or to avoid taking it before bed, is practitioner opinion rather than a finding [15].