Cellophane-wrapped bread, strawberry-flavoured yoghurt, wholegrain breakfast cereal, steak pasties, protein snack bars, gummy bears, hot dog sausages, supermarket cupcakes, microwave lasagne… The list of ultra-processed foods (UPFs) goes on and on.
Any food that is made industrially, with ingredients or techniques that you wouldn’t typically find in a home kitchen, is technically UPF. In the UK and US, that’s more than half of the average person’s diet.
As you may have suspected, this is unlikely to be a good thing. Eating more of this food is associated with a higher risk of a smorgasbord of health conditions, including obesity, type 2 diabetes, heart disease and various cancers.
If, while chomping on a ready meal, you glance at its long ingredients list, you might assume that all its unfamiliar additives are the main reason why.
You’re not totally misguided. Scientists have found evidence that some of the chemicals added to UPFs might lead to poorer health outcomes.
For instance, certain food dyes are associated with hyperactivity in children, some preservatives in processed meat have been linked with heightened cancer risk, and specific emulsifiers may damage the gut microbiome.
Clearly, that’s a problem – but it’s not the whole story. Increasingly, scientists are pointing to a less obvious culprit: texture.
“The reason that ultra-processed food is so bad for us isn’t just these additives and emulsifiers,” says Prof Sarah Berry, nutrition scientist at King’s College London.
“It’s partly that, but it’s not all about that. Ultra-processed food generally has had its texture changed so it’s very soft. What that means is, you eat it more quickly, so then you eat more of it.”
It may sound almost too simple to matter – softer foods are easier to eat. But that small detail is now beginning to reshape how scientists think about ultra-processed foods altogether.
We overconsume UPFs
If you want a clear glimpse of what UPFs do to our daily calorie intake, look to a landmark UPF study led by US nutrition scientist Kevin Hall.
For two weeks, the study’s 20 participants ate either a minimally or ultra-processed diet – and then, for another two weeks, they switched.
Meals were nutritionally matched for calories, carbs, protein, fat, sugar, salt and fibre, and the participants were allowed to eat as much or as little as they liked.
When individuals ate the ultra-processed grub, they ate an average of 500 calories extra per day – mainly from fat and carbs – compared to the less processed diet. They also gained almost 1kg (2lb) of weight.
The question is, why? When scientists analysed results from the Hall study, one major difference between the diets stood out: participants ate their ultra-processed meals more quickly.
We eat food faster when it’s softer. And, when manufacturers process food, they often break down ingredients’ natural structure to create soft, melty textures that don’t require laborious munching.
The study’s UPF meals were softer than their minimally processed counterparts, so participants could chow them down without much effort.
“We’ve been able to show for years and years now that to eat at a faster rate means you’re going to consume more energy,” says Prof Ciarán Forde, nutrition scientist at Wageningen University, the Netherlands.
In fact, when we speed up our eating by 20 per cent, Forde’s research has shown we tend to eat between 11 and 15 per cent more calories.
“Eating faster will drive intake up in any format,” he says. “Whatever it might be – the purest, most unrefined, most minimally processed food in the world – if you eat it fast, you’ll eat more of it.”
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People who tend to eat quickly in general are also more likely to be overweight, to have higher blood pressure, and to be at risk of type 2 diabetes.
“The first phase of digestion occurs behind your lips, not down in your stomach,” explains Forde. “You’re priming the body to receive nutrients, and so how you chew influences how you digest your meal, and how full you feel afterwards.”
When we eat, the muscles around the stomach stretch and gradually start to release fullness signals. But this process doesn’t happen instantaneously.
“There’s a small lag between eating and the change in chemistry to the brain,” says Forde. “We’ve done studies where, if you chew the same calories for longer, you get a stronger satiety secretion.”
That means if the food you’re eating is so soft that you barely need to chew it – like a lot of UPFs – you can eat a large portion before your brain gets the message that your body is full.
“One thing that all junk foods have in common is they’re often softly textured and energy dense,” says Forde. “So, you’re more likely to consume more calories and not necessarily be aware of it.”
Not all UPFs
At this point, you might be thinking that not all UPFs are soft. Some are crunchy or chewy – like protein bars or nutty granola. Wouldn’t those slow you down?
It’s exactly that line of thinking that led Forde to run another experiment. His team developed a trial similar to Hall’s – again with two diets, each followed for two weeks, that were matched for nutrition and likeability.
Except this time both diets were 95 per cent ultra-processed, and the key difference was texture. One diet contained chewier, crunchier, harder foods designed to be eaten slowly, and the other contained softer, spongier, wetter foods that could be eaten quickly.
“What we found was really striking,” says Forde. “With no instructions whatsoever to participants, just by giving them everyday foods in your supermarket, people ate on average about 370 calories less when they slowed down their intake.”
The study’s 41 participants didn’t just consume significantly more on the faster diet; they also gained more body fat, by nearly 500g (1lb).
“Of course, all of the foods in our trial were ultra-processed,” Forde adds. “So, you can make the statement that ‘most ultra-processed foods are softly textured and energy dense,’ but we found a whole separate set of ultra-processed foods that were eaten at a slower rate, and reduced intake.”
That marries with evidence from large observational studies, which found that not all categories of UPF are equally bad for us.
Interestingly, in studies that found links between UPFs and conditions such as type 2 diabetes, notable exceptions included wholegrain bread, flavoured yoghurt, plant-based meat alternatives and breakfast cereals.
Combine this with Forde’s texture-based work, and we can see that the ultra-processed category contains a spectrum of healthiness.
“Our results are sometimes hijacked as evidence that all UPFs are bad, and promote excess calorie consumption,” says Forde. “That’s a misappropriation of our outcomes.
“We’ve shown that we can move beyond these simple, binary, good–bad, processed vs not-processed discussions.”
Forde argues we should pay attention to “simple watchouts” such as calorific, rapidly-consumed foods – many (but not all) of which are ultra-processed – and swap them for “just as enjoyable” foods that take longer to eat.
“This could be part of a solution in the future,” says Forde. “If you want to add texture to your diet, you can make those changes within a realm of foods that you enjoy eating – and there are loads of processed foods that you can use to do that.
“You can enjoy the pleasure of eating, and feel satisfied and full, without having to feel bad about it.”
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