Many products contain added omega-3, but you can't always trust the claims on food labels, says Which?

The consumer watchdog tested the amount of omega-3 in a range of products - from oily fish where it occurs naturally, to foods where it has been added - and found up to 1,000% more or 98% less than the quantity declared. "And even the omega-3 that is present may not be doing you as much good as you think," the group warned consumers.

Omega-3 from plants is not as beneficial as that from fish, but this difference is rarely made clear on food labels, it claimed.

"Even products with added fish oil often fail to say just how much you'd have to eat or drink to get a useful amount of omega-3."

Tesco's Healthy Living pomegranate juice drink with added omega-3 came under fire from Which? as the group claimed consumers would have to drink 1.5l a day to get the advised daily amount.