Is tracking your food purchases good for your health?

With a packet of biscuits in one hand and her smartphone in the other in the biscuits sucrées aisle of her local Hyper U supermarket west of Paris, Nathalie sees red. Literally.

"Look at that!" she says showing me her phone. 0/100 is marked in red lettering.

"This is one of Malo's [her 12-year-old son's] favourites but it's not only full of sugar and saturated fats, there are four additives as well including one health risk," she says.

Nathalie clicks on the additive in question: E450. "A mineral which, taken in excess, can lead to bone marrow and kidney problems," she reads.

"Honestly, that they can put this sort of thing in food aimed at children drives me nuts!" she says.

We scan an Italian alternative whose packaging gives you the impression those biscuits have been hand-made by peasant women wearing black shawls.

The score is not much better: "Malo hates shopping with me now," says Nathalie. "You spend ages scanning and he can never have what he wants."

The app, having activated the red alert, suggests a healthier alternative. It's organic, containing wholewheat, fruit and fibre.

"You end up buying a lot more organic stuff so it's more expensive," she says.

Nathalie is one of a growing number of people using Yuka, an app developed in France, to shop more healthily. Not just for food but cosmetics and toiletries too.

Download it and you can use your phone to scan the barcodes of any one of the six million products on the Yuka database (about 1,200 new ones a day) and it'll tell you immediately – green for good, red for bad, yellow for could be better. If you want to know more, you can delve further. Pages and pages if you want.

Started in 2015, Yuka now has 85 million users in 12 countries: numerous European ones plus the US, Canada and Australia.

The third-biggest user is the UK with around five million, second is France with six million, but the biggest by a very long way is the US with 28 million.

Yuka has some high-profile fans in the US. For example, Donald Trump's Secretary of Health and Human Services, Robert F Kennedy Jr, says it's his favourite app.

Yuka has a traffic light system plus extra nutritional information

Yuka was founded in France where it still has its headquarters, but three years ago co-founder and CEO Julie Chapon moved to the States because the app was doing so well there.