Ultra-processed foods are often high in fat and sugar
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In recent years, there has been a growing demand from scientists, doctors and the media for ultra-processed food (UPF). Some have warned that the trend towards more and more processed foods in our diet is largely responsible for the enormous burden of chronic disease in the modern world. But what are UPFs, what makes them bad for you, and how concerned should you be?
The first question is surprisingly difficult to answer. Humans have processed food for millennia to make it tastier and last longer, for example by grinding grains, salting, drying, fermenting, pickling and smoking. The term ultra-processed food was coined in the late 2000s by Carlos Monteiro at the University of Sao Paulo, Brazil, who defined it as food created by breaking down whole foods into their constituents, such as sugar, fat and fiber, and chemically modifying them into products, often with additives. Things in this category include cereals, biscuits, fish fingers, ice cream, cakes, mass-produced bread and carbonated drinks.
Traditionally, healthy dietary advice has focused on nutritional composition: we are told to avoid foods high in salt, sugar and saturated fat, and choose foods high in fiber and vitamins. The idea of UPFs changed the conversation by suggesting that the degree of processing was more important when deciding which foods are unhealthy. Some countries, such as Brazil, Belgium and New Zealand, have changed their official dietary guidelines to encourage people to avoid these foods.
But is there evidence that UPFs are bad for you? There have now been more than 100 studies that have found that diets high in UPF are associated with poorer health, including a higher risk of cancer, diabetes, dementia, heart disease, bowel disease and obesity. But most of these only show a connection. Since this type of diet tends to contain things we know are bad for you, these studies don’t prove that the treatment itself is a problem. It is also difficult to separate the effect of diet from other lifestyle and environmental factors, such as poverty and pollution. And many of these studies rely on questionnaires, which are notoriously unreliable because people are bad at either remembering or honestly reporting what they eat.
The strongest evidence comes from a randomized study published in 2019 – but even this was only a small, short-term study. Twenty subjects were fed a diet high in either UPF or untreated food for two weeks, then switched to the other diet for another two weeks. The diets were similar in terms of total calories, energy density, protein, carbohydrates, fat, fibre, sugar and sodium. The volunteers were given three meals a day plus unlimited snacks, and they could eat as much or as little as they wanted.
On the UPF diet, volunteers ate about 500 more calories per day than on the untreated diet, and after two weeks they had gained an average of just under a kilogram. On the unprocessed diet, they lost just under a kilo. This suggests that the problem with UPFs is that they make us eat more calories. These foods are engineered to be delicious and moreish, easy to eat and digest, and we just can’t help ourselves.
But some scientists think there are other ways they can harm our health. They may be contaminated with toxins made in food factories. They often contain additives such as emulsifiers, and there is some evidence that these chemicals can be harmful. UPFs can also disrupt our microbiome and promote inflammation. Some advocates argue that UPFs should be subject to the same kinds of regulations as smoking: prominent warnings on packaging, restrictions on advertising, bans in schools and high taxes.
On the other hand, critics say the evidence is not strong enough to support such strict guidelines. They say the UPF label is too broad and can tarnish foods that are actually quite healthy, like yogurt and wholemeal bread. Even nutritionists struggle to agree when asked to categorize a range of foods according to their treatment level, so how is the public supposed to understand which foods to avoid? Also, not everyone has the time or money to cook nutritious meals for themselves every day. Demonizing UPFs could take away a valuable source of cheap and convenient nutrition.
So how worried should you be? While there are certainly problems with UPF as a category, it applies to many foods that are unhealthy and designed to encourage overeating. Most of us would benefit from having fewer UPFs and more whole foods in our diet. But avoiding them altogether is impractical and probably not necessary. By all means, cut back, diversify your diet and cook for yourself when you can. But don’t be rude if you fall back on ready-made pizza from time to time.
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