How ultra-processed food affects your brain

Ultra-processed foods now make up around 39% of the average Australian diet. We all know that eating too many ultra processed foods isn't great for your physical health. But how does it affect your brain?

Large population studies consistently link a high intake of ultra processed food with poorer cognitive and cardiovascular health. While researchers are still working to understand exactly why this happens, the evidence points to an important connection between the foods we eat and how our brains function over time.

What is ultra-processed food?

Not all processed food is unhealthy. Foods like tinned tomatoes, frozen vegetables, rolled oats and plain yoghurt are processed, but they only contain one ingredient and they're also nutritious and can be useful parts of a healthy, balanced diet.

The NOVA food classification system helps distinguish between everyday processed foods and ultra processed foods. Ultra-processed foods are defined in the NOVA system as:

“Typically containing 5 or more ingredients, including substances extracted from foods and substances derived from further processing of food components. Ultra-processed foods can also contain food additive classes such as colours, flavours, non-sugar sweeteners, and processing aids.”

In an Australian supermarket, ultra-processed foods often includes:

• Soft drinks, energy drinks and flavoured milks
• Packaged snacks, biscuits and confectionery
• Instant noodles, packet sauces and breads
• Processed meats such as ham and bacon
• Flavoured yoghurts and cereals

What do ultra-processed foods do to the brain?

Research has found a clear association between eating more ultra processed food and poorer brain health.

A study of more than 14,000 adults in the United States found that every 10% increase in the proportion of ultra processed food consumed was linked to a 16% higher risk of cognitive impairment and an 8% higher risk of stroke.

People who ate more minimally processed foods showed the opposite pattern, with those foods appearing to have a protective effect. Similar findings have been reported in studies from Brazil and the United Kingdom.

Researchers still don't really understand why, though chronic inflammation, disruption of the gut microbiome, cerebrovascular damage and weight gain are all possible causes.

What intervention studies found about junk food

Observational studies can identify patterns, but intervention studies help researchers explore cause and effect.

A study at the US National Institutes of Health (NIH) had 20 adults to follow 2 carefully controlled diets. Participants spent 2 weeks eating an ultra-processed diet and another 2 weeks eating a minimally processed diet. Both diets contained similar amounts of energy, sugar, sodium, fibre, fat, carbohydrates and protein, and participants could eat as much as they liked.

Participants consumed around 2,100 kJ more each day while eating the ultra processed diet. They also gained approximately 0.9 kg during those two weeks, while losing weight during the minimally processed phase.

This was partly put down to ultra-processed foods often being softer, more energy dense and requiring less chewing, making them quicker to eat. Our brains usually need around 15 to 20 minutes to register fullness, regardless of what's on the plate. If you eat quickly, it's easier to consume more before your body tells you that you've had enough.

Ultra-processed foods' direct effect on the brain

Research from Virgina Tech shows a diet high in heavily processed foods can negatively impact the brain's ability to focus and increases the risk of developing dementia.

The study examined the diets and cognitive health of more than 2,100 Australian dementia-free adults middle-aged and older.

The findings demonstrate that a slight daily increase in a person's intake of ultra-processed foods is linked to a measurable drop in attention span even if someone otherwise eats healthy.

For every 10% increase in ultra-processed food a person consumed, there was a distinct and measurable drop in their ability to focus.

This meant consistently lower scores on standardised cognitive tests measuring visual attention and processing speed.

It is worth noting that most intervention studies run for only weeks, while cognitive decline develops over decades. Trials of this kind can capture short-term effects, but not the cumulative consequences of a lifetime of eating.

How much ultra-processed food is too much?

There's currently no clinically established “safe” amount of ultra processed food.

Instead of focusing on eliminating these foods altogether, researchers increasingly recommend thinking about what they're displacing from your diet. Every meal built around minimally processed ingredients is one less meal centred on ultra processed alternatives.

For many people, healthy eating doesn't need to mean following a restrictive diet. Small sustainable habits can make a meaningful difference over time. That might include

• Cooking with whole ingredients when you can
• Choosing vegetables, legumes, wholegrains, nuts and oily fish more often
• Using extra virgin olive oil as your main cooking oil
• Treating ultra processed foods as a sometimes food

Current nutrition research consistently supports dietary patterns centered on minimally processed foods for better long-term health, including brain health.