Even if you only have a passing interest in healthy eating, you’ll be aware of the latest food scare: ultra-processed foods or UPFs.
This is a catch-all term for foods that contain a long list of ingredients, such as takeaways, ready meals, pre-prepared pasta sauces and soups, most snacks and desserts, breakfast cereals – even most loaves of bread.
The idea has taken off that UPFs are behind the rising rates of obesity and related health conditions in the UK and most other countries. But it’s not clear what exactly it is about this kind of food that is so bad for us.
A range of culprits have been blamed, including artificial chemicals or the high fat, salt and sugar levels normally found in UPFs. Now a new study points to a different explanation – the fact that factory-made food usually has much less fibre in it than homemade meals, and that this nutrient may have powerful appetite-reducing effects.
It raises the question: does a focus on fibre suggest a way to get the health benefits of a wholefood diet without having to shun UPFs entirely and make all our meals from scratch?
When it comes to healthy eating, most experts have long considered only what food is made of, in particular, how much it contains of the chief dietary sins of fat, salt and sugar.
In the past few years, the idea has grown that the real explanation might be the takeover of the modern diet by UPFs – which now makes up nearly two thirds of the average person’s food intake in the UK.
That matters, because while most processed food is high in fat, salt and sugar, some isn’t – like wholemeal bread, baked beans, some pasta sauces and healthy versions of cereal and yogurt. So anti-UPF campaigns might lead people to miss out on those nutritionally useful foods, or just “dilute” the more evidence-based NHS food advice about eating less fat, salt and sugar.
Key to the problem is that while multiple studies have found people who eat more UPF are more likely to be overweight, we don’t know exactly which components of processed foods are responsible. That means we don’t yet know exactly how people should try to improve their diets.
The new study from Dr Aygul Dagbasi, at Imperial College London, suggests that much of the benefits of wholefoods comes from their fibre content.
The finding comes from asking 10 people to try different diets after having a thin tube three metres long threaded up their nose and down into their stomach, until it reached their intestines. “It’s really difficult to access this deep inside into the gut, because it’s so inaccessible,” says Dr Dagbasi.
When people spent a day eating homemade meals like chicken, peas and carrots, their intestines produced more of an appetite-suppressing hormone called PYY than another day when they ate similar food but in the form of UPF, which was lower in fibre. “Diets high in processed foods may be keeping us less full, therefore we may be eating more calories, eventually leading to weight gain,” she says.
While most UPF campaigners agree the low fibre content of processed food is one of its problems, there has been a recent focus on other potential explanations for its harms, especially its long list of artificial ingredients, like preservatives, sweeteners and emulsifiers.
Other theories include the fact that UPF is often made using “industrial processes”, and often involves reducing foods to core ingredients, like high-fructose corn syrup or hydrolysed protein, which are then reconstituted into products such as cakes and veggie burgers.
If those ideas are right, that means we should try to cut out all UPF or at least, eat as little as possible, as argued by Dr Chris van Tulleken’s in his book Ultra-Processed People: Why Do We All Eat Stuff That Isn’t Food…and Why Can’t We Stop?.
If fibre really is key, that’s good news as it suggests that people could get some of the benefits of whole foods without giving up more convenient processed foods – by just adding more fibre-rich foods to their diet.
Foods high in fibre include pulses such as peas, beans and lentils, wholemeal bread, pasta and rice, as well as nuts and seeds, according to Dr Duane Mellor, a dietitian and spokesperson for the British Dietetic Association.
Fibre expert Dr Jens Walter at Ireland’s University College Cork says one of the easiest ways to boost a meal’s fibre content is to add a side of garden peas. “Peas are one of my go-tos,” he says.
Another of his quick options is oven-baked carrot batons mixed with broccoli stalks and quartered onions, coated with olive oil. “I like it when they get slightly crispy and caramelised,” he says. “I bulk up every single meal.”
Some people also use fibre supplements, such as Fybogel, a powder that is turned into a drink. But it is unclear if this form of fibre gives the same benefits as fibre naturally present in food, says Dr Walter: “It’s still an open question.”
The new research isn’t the last word on the explanation for why UPF may be bad for us – not least because it was a small study, and needs to be repeated by other researchers. It’s also possible that fibre is just part of the explanation, with other things going on too, says Dr Dagbasi.
“This is another piece of the puzzle, which helps explain human appetite and weight control,” says Dr Mellor. “I think it will wake us up to the need to recognise the importance of fibre.”