CLA (Conjugated Linoleic Acid)

Supplements · Fatty Acids · Supplement, Typed Supps

A modified fat sold as a fat burner — the real effect is tiny.

Stage by stage

Intake (Softgel): Digested like other dietary fats.
Small intestine (Standard fat absorption): Absorbed alongside dietary fat.
Bloodstream (Incorporated into tissue): Carried through the blood to fat and muscle tissue.
Body composition (Modest, inconsistent effect): Studied for effects on body fat percentage, with results that are small and inconsistent across trials.

Reducing body fat — limited evidence. Meta-analyses find a statistically significant but very small reduction in fat mass (on the order of a few hundred grams), widely judged to be below clinical importance.
Producing meaningful weight loss in real-world use — insufficient evidence. Despite heavy marketing, pooled effects on body weight are trivial and inconsistent, so it does not deliver the fat loss it is sold for.
Evidence that it causes Worsening blood-sugar control and liver enzymes — limited evidence. A pooled analysis found CLA raised fasting glucose and one liver enzyme (AST); animal data show fatty liver and insulin resistance at high doses. The signal is a reason for caution rather than proof of harm.

Around 3–3.4 g/day in trials

Upper limit: No established UL; higher doses raise the metabolic-safety concerns above

With food, standard dosing.

Diabetes medication (metformin, insulin, sulfonylureas): Not a pharmacokinetic interaction. A pooled analysis of trials found CLA raised fasting glucose, which pulls against what the medication is doing. If you take it alongside diabetes treatment, monitoring is sensible — and it is fair to ask what you are getting in return for that, given how small the fat-loss effect is. (moderate)
Medicines requiring liver-enzyme monitoring (statins, methotrexate, isotretinoin): The same pooled analysis found CLA raised AST, and animal work shows fatty liver at high doses. It can muddy the interpretation of routine liver-function monitoring, so tell whoever orders the test that you take it. (moderate)

“CLA is a proven fat burner.” In reality: Meta-analyses generally show only a very small effect on body fat, well short of its marketing reputation.