Conjugated linoleic acid (CLA)

About Conjugated linoleic acid (CLA)

A group of positional and geometric isomers of linoleic acid found naturally in ruminant fat and dairy. Supplements are made from safflower oil and contain roughly equal amounts of the cis-9,trans-11 and trans-10,cis-12 isomers, which behave very differently.

CLA is the clearest example in this group of a supplement whose animal data never survived contact with people. In mice, the trans-10,cis-12 isomer produces dramatic fat loss; in humans, meta-analyses put the average effect at roughly 0.05 kg of fat per week, which over six months is a change most people would not detect. The same isomer has been shown in controlled trials to worsen insulin sensitivity in overweight men, to lower HDL cholesterol and to raise markers of oxidative stress and liver enzymes. Naturally occurring CLA in dairy fat is a different exposure from a supplement enriched in the isomer that causes the problems.

Sold as

Softgel, Oil, Powder

Standardised to

Usually 78–80% total CLA as a roughly 50:50 mix of the two active isomers — a product without this marker may not resemble what was studied.

Also known as

CLA, Conjugated linoleic acid, Rumenic acid

Regulation: Sold as a dietary supplement in the US with no pre-market efficacy or safety review. EFSA has assessed CLA health claims for weight and body composition and concluded a cause-and-effect relationship was not established.

What the research used

The amounts, forms and durations published trials of Conjugated linoleic acid (CLA) actually administered.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.