Also known as: Conjugated linoleic acid, Tonalin, Clarinol, t10c12 CLA, Safflower CLA
Fat MetabolismEmerging evidence
A modified fatty acid sold for fat loss since the 1990s. The animal data was striking, the human data was not, and the isomer responsible for any effect is also the one raising concerns.
Typical dose
3.0–6.0 g per day
With meals, split across the day
What it is
Conjugated linoleic acid is a group of isomers of linoleic acid, an omega-6 fat, in which the double bonds sit in different positions. It occurs naturally in beef and dairy from grass-fed ruminants.
Supplements do not use the natural mixture. They are made industrially from safflower or sunflower oil and contain roughly equal amounts of two isomers: c9t11 and t10c12.
That distinction matters more than it sounds. The natural form in food is predominantly c9t11. The t10c12 isomer, which is responsible for the body composition effects, is present in supplements at levels far above what any diet would supply, and it is also the one linked to the metabolic concerns below.
How it works
The t10c12 isomer appears to inhibit an enzyme involved in storing fat in fat cells, and to influence the transcription factors that govern fat cell development.
There is also evidence of increased fat oxidation and energy expenditure, though effects are small at achievable doses.
The complication is that the same isomer has been associated in some research with reduced insulin sensitivity and unfavourable shifts in lipid markers. The mechanism that produces the effect and the mechanism that produces the concern are the same one, which is unusual and makes the risk-benefit calculation genuinely awkward rather than simply cautious.
What the evidence shows
Animal research, particularly in mice, showed dramatic reductions in fat mass, which is what launched the category. Those results have not translated proportionally to humans.
Meta-analyses of human trials report fat mass reductions of roughly 0.5 to 1 kg over six months. That is statistically detectable and, over six months of daily supplementation, of questionable practical value.
Some trials have reported unfavourable changes in insulin sensitivity and lipid markers alongside the modest fat loss. Given the small benefit, those findings weigh more heavily than they would if the effect were larger, and they are the main reason to be cautious rather than merely unimpressed.
Dosing
Trials have typically used 3 to 6 g daily, split across meals. This is a substantial amount of oil, usually taken as several large softgels.
Take with food, since it is a fat and absorbs better alongside a meal.
Be realistic about what the evidence supports: around half a kilogram to a kilogram of fat mass over six months, alongside some findings that give reason for caution. If fat loss is the goal, the diet and training that produce it are the thing to invest in, and this is not where a limited budget should go first.
At a glance
Common forms
Safflower-derived CLA softgels, Tonalin, Clarinol, CLA powder, Within fat loss blends
Half-life / duration
Incorporated into tissue over weeks; trial effects assessed over 3-6 months
Timing
With meals, split across the day
Competition status
Permitted — not on the WADA Prohibited List
Category
Fat Metabolism
Safety and side effects
The most commonly reported effects are digestive: nausea, loose stools and abdominal discomfort, generally mild and dose-related.
The more substantive consideration is metabolic. Some trials have reported reduced insulin sensitivity and unfavourable lipid changes with the t10c12 isomer at supplemental doses. This is not a universal finding, but it is repeated enough to matter.
Take particular care if your blood sugar or lipids are being monitored, and speak to your doctor before use in that case. There are also isolated reports of liver-related effects at higher intakes.
Who should avoid it
Take particular care if your blood sugar or lipid levels are being monitored, and speak to your doctor first — some trials report unfavourable changes in both. Avoid if you have been told your liver is not working normally. Speak to your doctor before use if you take regular medication. Not established in pregnancy or breastfeeding.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
