It is in your coffee, your smoothie and, it would seem, your entire social media feed, and most of the positive studies have been paid for by people who sell it.
The claim
The claim is everywhere, generally accompanied by a photograph of someone laughing at a salad. To test it properly, we looked through the systematic reviews and large trials, setting aside the single small studies that tend to produce the most exciting newspaper headlines and the least reliable answers.
Check who paid for the study before you pay for the tub.
The studies
The strongest evidence comes from randomised controlled trials, and here there are a few good ones. Results lean in a positive direction, although the effects are small, and they vary considerably among different groups of people. Observational studies look far more impressive, as observational studies very often do.
Our verdict
Beware of the phrase "linked to". It may mean a causal relationship, but it may mean only that people who do one healthy thing tend to do lots of other healthy things as well. Careful researchers try to adjust for this. No one can ever adjust for it entirely.
Our verdict is at the top of this page. It is unlikely to do you any harm, and it may help a little, but it will not replace the basics. Please do be sceptical of anybody who offers you certainty, particularly if their website also has a shopping basket.
