How ultra-processed foods are rewiring your brain, from white bread to ready meals

Anyone who has ever found it hard to stick to just one or two biscuits without wanting to devour the entire pack will recognise that ultra-processed foods (UPFs) can be extremely addictive – and scientists are starting to figure out why.

Earlier this year, a new study by Canadian neuroscientists provided the latest hints on how UPFs might rewire our brain chemistry to make it harder to stop eating them.

While examining MRI scans of thousands of British people who consumed varying amounts of UPFs, researchers found a link between eating higher quantities of UPFs and changes in the structure of key brain regions. In particular, they noticed changes in the hypothalamus, a region involved in regulating the appetite, and also in the nucleus accumbens, which is the brain’s pleasure centre.

According to Filip Morys, a researcher at the Montreal Neurological Institute who led the study, this observation could explain why people who consume a lot of UPFs are more likely to experience weight gain, lose control of their eating habits and be at risk of obesity. “Most of the changes we observed were very specific to brain regions involved in feeding and reward-related behaviours,” says Morys.

Other studies of UPFs have drawn similar conclusions, with another notable experiment finding that simply eating a small high-fat snack on a daily basis can drive long-term brain changes. Ashley Gearhardt, a professor of psychology at the University of Michigan, says that the reason they can rewire our neural circuitry is because their concoctions of ingredients activate the pleasure centre and reward networks in our brain, causing them to become dependent on abnormally intense levels of stimulation.

Because of this, she equates the addictive nature of these foods with cigarette smoking, as the nicotine you inhale when you puff on a cigarette hijacks a natural biological system which the body normally uses to regulate memory, attention and mood by mimicking the behaviour of a natural brain chemical called acetylcholine.

“UPFs are engineered to hijack the brain’s reward systems in much the same way,” says Gearhardt.

So what are some of the common culprits which we’re encountering on a regular basis?

The UPFs in your kitchen

It might be easy to think of UPFs as simply burgers and takeaways but in reality, their presence within our lives is far more insidious. Ready meals – consumed by approximately 88 per cent of all UK adults, with two in every five people eating them on a weekly basis – are a classic example of a UPF.

Tim Spector, an epidemiology professor at King’s College London and founder of ZOE, lists protein bars, flavoured yoghurts and condiments as other key examples of UPFs. He says: “They’re often packed with artificial sweeteners, emulsifiers, stabilisers and other high-risk additives, even if they look healthy. A good example would be certain sauces which people don’t usually think of as UPFs but can contain lots of sweeteners and additives.”

Importantly, Spector notes, not all UPFs are created equal. How addictive they’re likely to be depends on the level of processing, which is why health tech companies like ZOE are working to develop new technology which allows consumers to take a supermarket product, scan its barcode, and see where it sits on the spectrum according to a “processed food risk scale”.

As an example, Spector says that while Weetabix is technically a UPF, it’s actually low risk because of its high fibre content and minimal additives. Traditional forms of white bread bought in a bakery are also processed foods, but they are also classed as low risk because they are simply made from just flour, water, yeast and salt. Spector notes that the more industrially-packaged versions, however, can be a different story, as many of these products are filled with emulsifiers, preservatives and added sugars.

Let’s take a deeper look at some of the problematic ingredients found in UPFs and why they might be capable of altering our brain’s responses to push us into eating more of them.

The brain-hijacking UPF ingredients

Salt

When you buy sliced bread in a supermarket, it’s worth looking at the salt content. According to the NHS, adults should consume no more than six grams a day – and bread can be a surprising culprit. The campaign group Action on Salt found that three in four sliced breads contained just as much or more salt per slice than a packet of ready salted crisps.

According to Gearhardt, salt can accentuate food cravings by amplifying sweetness and other biological and sensory cues which keep people coming back for more. “Salt does more than just make food taste better,” she says. “It also strengthens the appeal of other addictive components [in UPFs] such as refined fats and carbohydrates.”

In the Canadian study, researchers also noted that the brain changes observed in people who consumed high amounts of UPFs were at least partly mediated by systemic inflammation, which can be exacerbated by excessive salt intake. “This can activate the body’s stress and inflammatory pathways which have downstream effects on the brain,” says Gearhardt. “That may blunt the brain’s ability to regulate cravings and fullness over time.”

Fructose

Whether it’s fruit juices “from concentrate”, fizzy drinks, condiments, baked goods or sweets, many UPFs are flavoured with this simple sugar. According to Gearhardt, the problem with consuming a lot of fructose is that it causes rapid spikes in blood sugar which then triggers the brain chemical dopamine, which is intrinsic to the brain’s reward systems. “This can overstimulate these pathways in the brain that evolved to help us seek out energy-rich foods,” she says.

Refined carbohydrates

In fruits and vegetables, carbohydrates come packaged alongside fibre, water and various micronutrients which slow digestion and promote fullness.

However in most UPFs, such as snacks, ready meals, packaged bread, instant soups or frozen desserts, carbohydrates are refined or essentially predigested. They are often disguised under the moniker of starches – you might recognise the terms “modified starch”, “cornstarch” or “potato starch” on many labels – and are used to thicken products and blend ingredients together.

A decade ago, a study carried out by Gearhardt found that foods high in refined carbohydrates were rated as having higher addictive qualities. She says that this is because they are absorbed so quickly in the mouth and gut, which then floods our system with glucose and triggers a sharp dopamine hit followed by a crash. Over time this pattern makes us less responsive to normal foods and more dependent on the intense stimulation provided by UPFs.

“This constant rollercoaster can change how the brain responds to food, driving cravings and making these foods genuinely addictive for some,” says Spector. “It’s one reason why we find ourselves reaching for another biscuit or bowl of sugary cereal, even when we’re not really hungry.”

High levels of fats and sugar

Richard Hoffman, a nutrition researcher at the University of Hertfordshire, reminds us that high levels of sugar and fat rarely occur together in natural foods. In UPFs, however, the two ingredients are regularly blended together.

Gearhardt says that this combination has a dramatic effect on dopamine, causing it to surge three times higher than baseline levels. This also makes us more susceptible to becoming addicted to these foods. Alexandra DiFeliceantonio, an assistant professor at Virginia Tech, says that studies have even found that combinations of fats and sugars are encoded markedly differently in the brain.

Emulsifiers and stabilisers

Without emulsifiers and stabilisers, it simply wouldn’t be possible for UPFs to contain complex blends of fat, sugar and refined carbohydrates. They also prevent products from spoiling over time. The presence of stabilisers is why UPFs can still be consumed after many weeks or months.

While they don’t directly affect the brain in the same way that added salt, fructose, or refined carbohydrates do, some additives may still have more subtle long-term effects by increasing inflammation in the body – for example, by disrupting the gut microbiome. “There is emerging evidence that some emulsifiers and additives lead to inflammation in the gut,” says DiFeliceantonio. “This could possibly lead to higher systemic inflammation.”

Additionally, Spector points out that these emulsifiers create the soft, easily digestible textures that make many UPFs so easy to overconsume, increasing the likelihood that our brains become hooked on their pleasurable signals.

Dyes

The addictive signals UPFs send to our brains come not only from taste, but also from factors like packaging and colour, which hack both our visual senses and our tongues.

“These additives serve a powerful psychological and sensory role,” says Gearhardt. “Colourants, artificial flavours and texture agents are designed to intensify the sensory impact of food – bright colours, creamy textures and rapid flavour bursts that fade quickly and prompt another bite. Industry insiders have openly described this as designing to amplify craving and promote indulgence.”

Spector explains that there isn’t one single ingredient which explains why UPFs are hacking our brain chemistry. Instead, it’s the combined effect of dozens of these chemicals. He says: “The bigger issue is that the system produces foods that are designed to be cheap, addictive and long-lasting rather than nourishing.”