Little is known about how they potentially interact with medications
Scientists are warning that not enough is known about the long-term safety of modified foods which claim to be good for your health.
Yoghurts designed to be good for your heart and margarines which claim to help lower cholesterol are among the so-called "functional foods" highlighted by experts.
And while there is no data showing the foods cause harm, little is known about their long-term safety or how they potentially interact with medications, they said.
Writing in the British Medical Journal, the experts from the Utrecht Institute for Pharmaceutical Sciences in Holland said the active health-drink market is one of the fastest growing in the UK, with a turnover of £316m in 2005.
They added fears over the way phytosterol and stanol-enriched products, such as margarines, interact with cholesterol-busting statins have led to health authorities in Canada prohibiting the sale of the foods.