Most of us know we are supposed to avoid eating too much ultra-processed food, or UPF. But did you realise it could be sending you to an early grave?
At least, that is the latest claim, based on a new study that found processed food is responsible for one in seven premature deaths.
It is enough to make you bin all the junk food in your house. But anyone thinking of doing so might want to first consider the range of opinions about UPF among doctors, dietitians and food scientists.
The idea that junk food is bad for us is not new. Gastronomists have long turned up their noses at takeaways, microwave meals and snacks like sweets or crisps. And doctors say we should avoid such foods because they are high in fat, sugar and salt.
But the more recent concept of UPF is a lot broader. It covers anything that is made in a factory, including any pre-prepared foods that contain ingredients you wouldn’t find in a typical kitchen.
Artificial chemicals
Some campaigners say it is bad for us because of the artificial chemicals, like preservatives, sweeteners and emulsifiers. Others, that it is because the food is made by breaking down raw ingredients into their constituent chemicals, and modifying and reassembling them, to make, for instance, hydrolysed vegetable proteins or high-fructose corn syrup.
Whatever the explanation, the category of UPF includes a lot of food that has long been seen as good for us, like most wholemeal bread and breakfast cereals that are low-sugar and high-fibre. It would also include baked beans, hummus, diet foods and veggie sausages and burgers.
As UPF makes up more than half of a typical Briton’s diet, anyone trying to seriously cut down would have to radically change the way they eat, by making all their meals and snacks from scratch. They would even have to bake their own bread or buy expensive artisan loaves.
Such a change would be worth it if it improved our health. But the evidence that it would is a lot weaker than it might appear.
The latest research is case in point. The scientists analysed seven previous studies that found correlations between the amount of UPF people ate and their likelihood of dying over a certain period.
Overall, for every 10 per cent increase in UPF, people had a 3 per cent higher risk of death.
The scientists then used existing data about typical diets in different countries to calculate that UPF causes 14 per cent of “premature deaths” in places such as the UK and the US, where it makes up a lot of the diet. Premature deaths are defined as those occurring between the ages of 30 and 69. The study was published in the American Journal of Preventive Medicine.
But that conclusion hinges on whether the figures were right from those seven previous studies.
Questions over the reliability of research into UPF
These were of a kind known as “observational studies”, meaning that they are less reliable than the gold standard of medical evidence, the randomised trial.
Observational studies can be biased by the fact that, for instance, people on lower incomes tend to eat more processed food, and tend to die earlier for other reasons, like smoking and drinking more. “People who consume UPF might have a much less healthy lifestyle,” said Professor Gunter Kuhnle, a nutrition researcher at the University of Reading, who wasn’t involved with the study.
Almost all previous studies showing harm from UPF are of this type of observational research. One randomised trial has been done, and this found that people offered unlimited processed food ate more than when given home-cooked food. But that trial had only 20 people in it and they tried each diet for just two weeks.
Dr Eduardo Nilson, a nutrition researcher at the University of São Paulo in Brazil, who carried out the latest study, said that it was too hard to carry out long-term randomised trials of different diets. “We have to rely on the available evidence,” he said.
Observational studies have previously been relied on to show that smoking causes lung cancer, he added, a finding that is now accepted.
But smoking has a much stronger impact on lung cancer, raising the risk by about 20-fold (or 2,000 per cent). Compare that with this study’s claimed 3 per cent raised risk of death from eating 10 per cent more UPF. “The effect size is so tiny,” said Professor Kuhnle. “I seriously doubt you can measure 3 per cent with any reliability.”
Government science advisers have previously said that the studies on UPF so far are “concerning”, but that the evidence is so uncertain, it should not change healthy eating guidelines.
In the UK – as in most countries – advice remains that we should eat food that is low in fat, sugar and salt, and high in fibre – whether it was made in factories or cooked from scratch at home.
“We already have dietary guidance on reducing high-fat, high-sugar foods, and that is relatively easy for the consumer,” said Dr Nerys Astbury, a nutrition scientist at the University of Oxford. “Making dietary recommendations on UPF is going to make that very confusing.”
Perhaps, the latest claims about UPF should be taken with a pinch of salt.