The new science on what ultra-processed food does to our brains

Studies are finding links between these foods and changes in the way we learn, remember and feel, Indeed, they describe them as almost addictive.

Many ultra-processed foods hit the brain rapidly when we eat them and have a strong effect on its reward system, which is involved in pleasure, motivation and learning.

Ultra-processed foods may not only affect our bodies, but our brains too.

Research suggests links between ultra-processed foods – such as chips, many cereals and most packaged snacks – and changes in the way we learn, remember and feel.

These foods can act like addictive substances, researchers say, and some scientists are proposing a new mental health condition called “ultra-processed food use disorder”. Diets filled with such foods may raise the risk of mental health and sleep problems.

The science is still early and researchers say there is a lot they don’t know. Not all ultra-processed foods are equal, some scientists say, adding that some might be good for you. A diet high in ultra-processed foods has been linked with obesity, type 2 diabetes, cancer and cardiovascular disease, but researchers are still figuring out exactly why, beyond calorie counts and nutrient composition.

Makers of foods such as processed meats and muffins defend their products, and note there isn’t a consistent, universally accepted definition of ultra-processed food.

Many ultra-processed foods hit the brain rapidly when we eat them and have a strong effect on its reward system, which is involved in pleasure, motivation and learning.

Those effects are similar to ones when people use nicotine, alcohol and other addictive drugs, says Ashley Gearhardt, a professor of psychology at the University of Michigan, who is a co-creator of a measure of food addiction.

“People intensely crave ultra-processed foods and consume them compulsively and find they can’t stop eating them,” she said.

The way foods are produced might partly explain why. To make items such as chips, breakfast cereals and snack bars, manufacturers often break down the cellular structure of ingredients, stripping them of water and fibre, making them easy to chew, eat and digest quickly. The components hit our brains fast, making the foods more addictive, Gearhardt says.

The combination of high levels of both fat and carbs in many ultra-processed foods is likely another reason why we crave them and have a tough time stopping when we eat them.

Chocolate, ice cream, pizza and chips are among the top foods people report eating in an addictive way, according to Gearhardt’s studies. Many of these are high in both refined carbohydrates and fat, a combination that isn’t typically found in nature. Foods in nature are often high in fat or carbs, but not both.

“Bananas are naturally high in sugar but you eat one and you’re good,” Gearhardt says.

In a recent study published in the journal Cell Metabolism, researchers primed participants with two different kinds of snacks and saw how their brains later responded to a cue for a high-fat, high-sugar food, which many ultra-processed foods are.

Scans of their brains showed the participants who ate a high-fat, high-sugar snack for eight weeks had much higher activity in parts of the brain that create dopamine, a neurotransmitter involved in motivation, learning, and expecting and experiencing rewards, when they saw a cue telling them to expect another high-sugar, high-fat food.

“When they see the sign of their favourite fast-food place or the packaging of their favourite snack, they have more brain activity and are potentially feeling more craving activity that could make them more likely to consume that food,” says Alexandra DiFeliceantonio, associate director of the Centre for Health Behaviours Research in Virginia, who was a co-author of the study.

Scientists were surprised to find that people who had been eating the high-fat, high-sugar snack also had changes in how their brains learned.

While participants were having their brains scanned, the researchers had them do a basic learning task, requiring them to push a button associated with a picture when they heard certain tones.

When people who had been eating the high-fat, high-sugar snack did not get the picture they expected, their brains showed greater activity in parts involved in evaluating situations. This high-sugar, high-fat diet “is changing something really basic about how we learn”, DiFeliceantonio says.

In a different study, four days of having a breakfast high in saturated fat and added sugar was linked to reductions in performance on some learning and memory tests, according to researchers in Australia. People who had a healthier breakfast did not have the performance changes.

Mental health is also affected by diet. Several recent studies have found a link between diets high in ultra-processed foods and an increased risk of depression. A large review of research published last month in the British Medical Journal found an increased risk of depression, anxiety and sleep problems with diets high in ultra-processed foods.

Gearhardt and colleagues are proposing a new mental health disorder they plan to call “ultra-processed food use disorder” or “highly processed food use disorder” for inclusion in the official guide that psychiatrists and psychologists use to diagnose patients.

Symptoms include intense cravings, difficulty cutting down consumption and withdrawal symptoms such as irritability and agitation when people try to reduce their intake.

One of the main ways diet affects mental health is likely via the gut microbiome, says Felice Jacka, director of the Food & Mood Centre at Geelong’s Deakin University.

The gut microbiome refers to the microbes that live in the digestive tract. It influences immune function, the stress response system and the production of neurotransmitters such as serotonin, all of which affect mental health, Jacka adds.

Eating a diet full of ultra-processed foods can change your microbiome so it is less diverse and has fewer types of beneficial bacteria.

Changes in the brain’s reward system caused by high-fat, high-sugar foods could also likely feed into mental-health problems, DiFeliceantonio says.

“The fact that your diet is altering that reward system pretty profoundly actually means that everything in your life is being affected,” she says.

The Wall Street Journal