CLA (Conjugated Linoleic Acid)

The verdict

Is CLA worth taking?

CLA is one of the most extensively studied weight loss supplements in existence and one of the most consistently disappointing when the full literature is examined. Animal studies, particularly in mice, showed dramatic fat loss effects. Human studies showed modest, inconsistent, and clinically questionable results. The isomer problem is critical and rarely explained on commercial products: the t10,c12 isomer drives most metabolic effects but also drives insulin resistance, increases CRP (an inflammatory marker), and may worsen liver enzyme markers in some trials. The c9,t11 isomer is considered safer but has less metabolic activity. Supplement CLA from safflower or sunflower oil delivers both isomers in roughly equal proportion with no ability for the consumer to separate them.

What it does

What CLA does in the body

Marketed for fat loss, lean mass preservation, and body composition improvement. The reality is a modest, inconsistent effect that has not held up under scrutiny in well-designed human trials, alongside a safety picture that raises legitimate long-term concerns that most product marketing does not acknowledge.

The evidence

What the research actually shows

Overhyped. A 2024 review in Nutrients explicitly described CLA’s effects on obesity as showing inconsistent findings due to dose-dependent outcomes and individual variability, with the dual nature of CLA showing both beneficial and adverse effects raising questions about long-term safety. A comprehensive review concluded no consistent result was observed even in similar studies at different laboratories. The t10,c12 isomer specifically has been shown to increase insulin resistance in abdominally obese men in multiple trials, a finding that is directly counterproductive to fat loss goals and is almost never mentioned in commercial CLA marketing. Consumer-facing evidence summaries are unusually direct on this one: most research shows CLA does not improve cholesterol levels or help with weight loss.

Food first

Getting CLA from food

Grass-fed beef and full-fat grass-fed dairy contain natural CLA predominantly as the c9,t11 isomer, which is the safer and more favorably studied form, in contrast to the mixed-isomer commercial supplements derived from chemically processed vegetable oils. If CLA intake is a goal, these whole food sources represent a meaningfully better choice than supplemental CLA from non-ruminant vegetable oil sources.

What the guide adds

The part that is not on this page

Everything above is the assessment. What the guide adds for CLA is the protocol:

• Optimal Form
• Dose Range
• Bioavailability
• Purity Red Flags
• Stack With / Avoid

147 entries across nine categories, every one graded against the clinical literature the same way.

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About the author

Who graded this

Daniel Edlund is a Le Cordon Bleu-trained private chef in Los Angeles, a certified personal trainer and strength coach, and an internationally licensed massage therapist. Thirty years of strength training and fifteen years cooking in private estate kitchens. He is the author of The Complete Supplement Guide, which grades 147 entries against the clinical literature, and of The EASY Way to Organic Cooking, first published in 2013.

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This page is information, not medical advice. Supplements interact with prescription medication and with each other, and the right answer depends on your own bloodwork and history. Talk to your doctor before starting anything, particularly if you are pregnant, nursing, managing a health condition, or already taking medication.

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All 147 entries, graded →