Ultra-processed foods – such as chicken nuggets, ice cream and breakfast cereals – have been linked to early death and poor health, scientists say.
Researchers in France and Spain say the amount of such food being eaten has soared.
Their studies are not definite proof of harm but do come hot on the heels of trials suggesting ultra-processed foods lead to overeating.
Experts expressed caution but called for further investigation.
What are ultra-processed foods?
The term comes from a way of classifying food by how much industrial processing it has been through.
The lowest category is "unprocessed or minimally processed foods", which include: • fruit • vegetables • milk • meat • legumes such as lentils • seeds • grains such as rice • eggs
"Processed foods" have been altered to make them last longer or taste better – generally using salt, oil, sugar or fermentation.
This category includes: • cheese • bacon • home-made bread • tinned fruit and vegetables • smoked fish • beer
Then come "ultra-processed foods", which have been through more substantial industrial processing and often have long ingredient lists on the packet, including added preservatives, sweeteners or colour enhancers.
If a product contains more than five ingredients, it is probably ultra-processed, says Prof Maira Bes-Rastrollo, of the University of Navarra, citing a maxim.
Examples include: • processed meat such as sausages and hamburgers • breakfast cereals or cereal bars • instant soups • sugary fizzy drinks • chicken nuggets • cake • chocolate • ice cream • mass-produced bread • many "ready to heat" meals such as pies and pizza | meal-replacement shakes
How bad were the findings?
The first study, by the University of Navarra, in Spain, followed 19,899 people for a decade and assessed their diet every other year. There were 335 deaths during the study.
But for every 10 deaths among those eating the least ultra-processed food, there were 16 deaths among those eating the most (more than four portions a day).
The second study, by the University of Paris, followed 105,159 people for five years and assessed their diet twice a year.
It showed those eating more ultra-processed food had worse heart health.
Rates of cardiovascular disease were 277 per 100,000 people per year among those eating the most ultra-processed food, compared with 242 per 100,000 among those eating the least.
The rapid increase of ultra-processed foods over less processed foods, "may drive a substantial burden of cardiovascular diseases in the next decades," said Dr Mathilde Touvier, of the University of Paris.
So do these foods damage health?
"[The] evidence is accumulating," said Dr Touvier, noting "increasing numbers of independent studies". Prof Bes-Rastrollo said she was "very certain" ultra-processed foods were bad for health.
Last year, a link was made with an increased risk of cancer.
The challenge is being 100% sure. The studies have spotted a pattern between highly processed food and poor health but they cannot prove that one causes the other.
Those who ate the most ultra-processed food were also more likely to have other unhealthy behaviours, such as smoking, which the researchers tried to account for.
But there's no guarantee everything relevant was covered, says Kevin McConway, a professor of statistics at The Open University.
"These studies do increase my confidence that there's something real behind these associations – but I'm still far from sure."
Why might ultra-processed foods be bad?
The first trial of ultra-processed foods showed they led people to eat more and put on weight.
Researchers at the US National Institutes of Health monitored every morsel of food that volunteers ate for a month.
And when given ultra-processed food, they ate 500 calories a day more than when they were given unprocessed meals.
Other suggestions include: