Can processed and sugary foods harm the brain?

Sugary and processed foods are tasty, convenient and very tempting. You likely know about the damage they can do to your waistline and your heart, but have you ever thought how they might affect your brain?

Diets laden with ready meals, breakfast cereals, biscuits, fizzy drinks and other sugary and ultra-processed foods (UPFs) have been linked to cognitive decline and dementia.  Some research has even found that the hippocampus, the brain’s memory hub, is smaller in people who eat a lot of junk food.

In one study from 2022, more than 70,000 people aged 55-plus in the UK provided detailed information on their diet. All were free of dementia at the start of the study but, ten years later, 518 had developed the condition. That includes 287 people who had been diagnosed with Alzheimer’s disease. Alzheimer’s disease is one of the main causes of dementia. 

Those who ate more UPFs had a higher risk of dementia. The good news is that replacing 10% of UPFs in your diet with unprocessed or minimally processed food could reduce your risk of developing dementia by 19%.

Even a small change, such as having half an apple a day, instead of a bar of chocolate, may cut your risk.

(The definition of UPFs varies but they typically contain emulsifiers, preservatives, artificial colours and other substances that you wouldn’t find in your own kitchen. They also tend to be high in refined sugar, fat and salt. Examples include sausages, crisps, supermarket bread, fizzy drinks, biscuits, microwave meals and flavoured yoghurts.  Unprocessed and minimally processed foods include fruit & veg, milk, pulses, eggs, nuts and seeds.)

Another study, also from 2022, tracked the health of more than 10,000 people aged 35 and upwards for around eight years.  The participants told the researchers about their eating habits and underwent regular cognitive tests.  

Test scores fell over time, as might be expected with age, but they decreased more swiftly in those who ate more UPFs.  Specifically, someone who got at least 20% of their calories from UPFs saw their memory and thinking decline 28% faster than someone who ate less of these foods.

The link between processed food and cognitive decline was particularly strong in the under-60s and the researchers said that limiting UPF consumption, especially in middle-age, may help keep the brain sharp in years to come. 

The study’s lead author, Dr Natalia Gomes Goncalves, of the University of Sao Paulo, told Brain Health Network: “Cognitive decline, as well as neurodegenerative diseases, does not happen overnight. It is a long process. 

“The choices we make when we are younger do influence our cognitive health when we are older. Middle age is an essential period of life to adopt preventive measures through lifestyle changes, and this effort is worth it when we are older.”

The studies didn’t prove that processed foods were directly to blame but there are several ways they could harm the brain.

They might, for instance, damage the blood vessels.  This would reduce blood supply to the brain – and deprive it of oxygen and nutrients.  The researchers also point the finger at the high level of salt in UPFs and at chemicals that can leach out of the packaging.  Plus, if we are filling up on junk food, we are likely not eating healthier foods that can help nourish our brain.

Another intriguing possibility is that an unhealthy diet impairs the growth of the brain.  One study found that the hippocampus, the brain’s memory hub and one of the areas damaged in Alzheimer’s, tends to be smaller in people who eat lots of sugary, salty and fatty food than in those who eat more healthily.

Another study found that rats suffered memory problems – they found it harder to remember where they’d seen things before – when they drank sugary water (the water was sweetened with table sugar).  They also made fewer new brain cells in the hippocampus.

Here are some simple ways to cut back on processed foods and refined sugar:

• Eating out or ordering a takeaway? Remember that sweet and sour dishes, sweet chilli dishes and some curry sauces tend to be high in sugar.

• Swap sugary breakfast cereal for porridge topped with dried apricots or a few slices of banana.

• “I like to have fresh fruit available to grab and go as an easy snack,” says Dr Gomes Goncalves.

• Buy plain yoghurt instead of fruit yoghurt and pop some fresh, frozen or dried fruit on top.

• Batch cook and freeze to reduce your reliance on ready meals.