Eating junk food is all-round bad for you, as this expert explains

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Learn more about how to give your brain a boost with our articles on fatty acids and brain health, 10 ways to boost your brain power and the 6 supplements experts take.

I get asked about ultra-processed food (UPFs) a lot. The first time was about 10 years ago, but back then most people were more interested in salt, fat and sugar. Now, though, we talk about UPFs so much that we just use the initials, because it would take up too much of our lives to say it in full every time. Even the average person in the street has heard of them.

Exactly what we mean by UPF is a bit sketchy because there isn’t one agreed definition and there is plenty of nuance. Most people use the NOVA classification which says UPFs use ingredients that are not recognisable as food, such as emulsifiers (like xanthum gum), or that have undergone processes to alter them (like soy isolate). Nutrition research has evolved away from single nutrients like salt, fat and sugar as being the problem with our diets and is finding more and more that UPFs are causing problems for our health. Obesity, type 2 diabetes, heart disease and bowel cancer are all thought to be more likely if we consume a lot of ultra-processed foods. But that’s not all. There is growing evidence that UPFs can also affect our brain health. From mood, to brain-fog to dementia risk, the quality of our diet has a big impact. The thinking is still partly that what’s in our food is causing us problems, but also crucially what’s not in our food is a problem too. UPFs are often missing micronutrients and another vital ingredient: fibre.

I’m a nutritionist and here’s why UPFs are deadening your brain

The gut-brain connection (and why it matters)

The bacteria in our gut feed on the fibre we eat and if we don’t get enough fibre the consequences go way beyond feeling bloated. The gut influences every other organ system in the body, including the brain. A healthy gut will have a diverse microbiome of gut microflora which perform important functions like training the immune system, producing fuel for cells, making neurotransmitters like serotonin (often called the happy hormone) and extracting nutrients. The greater variety of fibre that we eat, the greater variety of bacteria our gut can support and the more effectively these processes can happen.

There’s now a mass of evidence that your gut health plays a crucial role in your mental health. The gut and brain are connected by the gut-brain axis – a two-way communication pathway that sends messages between them, and most of the messages come from the gut. A healthy gut microbiome helps regulate mood, stress responses and cognitive function.

Unfortunately UPFs can disrupt the delicate balance of the microbiome. They tend to be very low in fibre and high in refined carbs, unhealthy fats and emulsifiers – a combination that the microbiome really doesn’t like. Multiple studies suggest this can lead to increased inflammation, disrupted serotonin production and impaired cognitive performance.

How UPFs affect your brain

1. Cognitive decline

The more UPFs you eat, the faster your brain seems to age. Truly worrying is the link between UPF consumption and increased risk of dementia. A recent large study found that the more UPFs participants consumed, the faster their cognitive decline. So, limiting UPFs may help delay the onset of dementia which is important if we want to live well as we age.

2. Depression and anxiety

Diet tangibly affects mood. Several big studies and meta-analyses have found that higher consumption of UPFs is linked to symptoms of depression. This may be in part due to UPFs having an inflammatory effect. It is now understood that inflammation affects the brain as well as the rest of the body and people with depression and anxiety have been found to have high levels of inflammation. While at this stage the scientists are cautious about saying UPFs cause depression, the evidence is mounting. Having seen the difference that a better diet makes for people in my clinic, I believe the link could definitely be causal.

3. Concentration, focus and mental agility

Nutrients directly influence brain function and your brain needs a host of them to function efficiently. Omega-3 fatty acids, B-vitamins, zinc and magnesium (among other vitamins and minerals) are all necessary. UPFs tend to be low in these nutrients and without enough of them, memory, focus and learning can be affected, which can result in lower academic performance, problems with flexibility of thought and difficulty switching between tasks quickly. Additionally, carbohydrate foods that are ultra-processed cause blood sugar spikes and crashes, which affect us pretty quickly because the brain runs on sugar. Low blood sugar means the brain doesn’t have enough fuel and that can result in irritability (anyone ever felt hangry??) and brain fog.

4. Sleep and brain recovery

Higher UPF consumption is linked to a higher risk of insomnia, potentially because of disruption to the gut microbiome. Sleep is when repair and maintenance happens and the brain is doing all the jobs that it can’t do while you’re awake, like clearing out all the waste products that accumulate throughout the day and can clog up synapses (which increases risk of dementia). If UPFs are making us sleep less, these important jobs don’t get finished. And as a kicker, when people are tired they tend to reach for easy, convenient, energy-dense foods. A vicious cycle.

UPFs, dopamine and decision-making

Here's where it gets fascinating, but unfortunately in a slow-moticon-car-crash kind of way. UPFs can alter brain chemistry and structure, which in turn alters behaviour and decision making.

Eating highly processed foods causes a spike in dopamine, the neurotransmitter that is involved in motivation and reward. UPFs hijack this system because they are designed to taste good and have a great mouth-feel, all of which trigger the release of dopamine.

But just because we trigger this reward signal, doesn’t mean it actually feels good. We have all sometime or another got to the point where we don’t want to eat any more, but can’t help ourselves. That dopamine hit can create a repeating loop: eat the food, feel good temporarily, crave more. This is because UPFs can affect the prefrontal cortex, the part of the brain responsible for impulse control and decision-making. In other words, the more UPFs you eat, the harder it becomes to stop eating them, which is one of the reasons researchers are looking into whether UPFs could be addictive.

How to eat better for your brain

Having said all this, it’s important to remind ourselves that not all UPFs are the same. The term can also be confusing because it isn’t always the processing that is the issue. There are plenty of convenience foods that are great: I often recommend baked beans on toast to my clients, for example. Foods (even if they are highly processed) that are high in fibre, micronutrients and essential fats are going to be much better for us than foods that contain refined carbohydrates, lots of emulsifiers and lots of ingredients that aren’t made from food. I recommend getting into the habit of reading the ingredient labels on the food you buy. The fewer ingredients that aren’t recognisable as food, the better.

Happily the brain and the gut can, and do, change according to the environment they find themselves in, so reducing UPFs and increasing real, recognisable ingredients and home-cooked meals can get your brain (and the rest of the body) to a healthier place.