Can eating ultra-processed food adversely affect YOUR mental health as study shows eating regular takeaways not only damages your waistline
It has long been claimed that regularly eating ultra-processed foods – packaged products that contain lots of fat, sugar, salt and additives – can raise the risk of cancer, heart disease and diabetes.
But now some of the most high- profile scientists in nutrition are raising the alarm about another, surprising consequence of a junk food diet: mental illness.
On Thursday, top UK experts in the field of diet-related diseases and brain health came together for a major summit about the crisis in the quality of British food and its repercussions for our health.
The Mail on Sunday was granted a coveted seat at the prestigious event, held at the home of the country’s biggest motorsport convention – Goodwood. Amid the discussions about obesity and heart health were intriguing revelations from psychiatrists about the growing evidence of links between what we eat and our mental health.
Prof Edward Bullmore, a neuroscientist and psychiatrist, said ‘a revolution is inevitable’ in the way doctors treat mental illness. In some cases, the causes will be seen as the very same as those that trigger heart disease.
‘I am very sure that food affects mental health, and there is a good amount of evidence to link ultra-processed food with poor mental health outcomes,’ says Dr Chris van Tulleken, a BBC presenter and infectious disease expert
The warnings come a week after researchers from Harvard Medical School published one of the largest studies into the link between depression and ultra-processed food after tracking the eating habits of 31,000 women over 14 years
‘We used to think it wasn’t possible for harmful things entering the body to cause depression,’ he added. ‘But now we know this is conceivable.’
Others say it might not be a coincidence that as ultra-processed diets have become increasingly prevalent – made up of ready-to-eat meals, savoury snacks, processed meat and artificial sweeteners – the number of people seeking mental health treatment has soared.
‘I am very sure that food affects mental health, and there is a good amount of evidence to link ultra-processed food with poor mental health outcomes,’ says Dr Chris van Tulleken, a BBC presenter and infectious disease expert. ‘The data can be confusing, but I suspect we will find eventually that the relationship is causal.’
Dr van Tulleken spoke about his own mental health issues at the hands of ultra-processed food. Referring to his recent BBC documentary What Are We Feeding Our Kids?, he added: ‘My experience of going from having very little ultra-processed food to very high amounts was that I saw a direct impact on my mental health.’ In the programme, Dr van Tulleken ate virtually nothing but ultra-processed food for a month before undergoing health tests.
‘I felt awful. [Ultra-processed food] dehydrates and constipates you, and that leads to you to not sleeping very well. I had increased depression and anxiety. At the end of the experiment, when I stopped being constipated, sleepless and thirsty in the middle of the night, my frustrations diminished. Most of that just went away.’
The warnings come a week after researchers from Harvard Medical School published one of the largest studies into the link between depression and ultra-processed food after tracking the eating habits of 31,000 women over 14 years. Even after accounting for other factors that could affect mental health – such as alcohol intake, body weight and lack of sleep – eating nine portions of these foods per day was associated with a 50 per cent increased risk of depression, compared with those who ate four or less.
‘The research is now pointing to structural brain changes as a result of what we do or don’t eat,’ said Kimberley Wilson, a psychologist specialising in nutrition and a co-presenter of the BBC podcast Made Of Stronger Stuff
The scientists found this relationship was particularly strong in those who consumed above-average quantities of artificial sweeteners found in fizzy drinks, for example. What’s more, there is even research linking these foods to a greater risk of dementia.
So what exactly is going on?
The reasons why ultra-processed food is bad for the body are relatively well publicised.
First there are the large quantities of calories, salt, fat and sugar, increasing the risk of weight-gain along with heart disease. Then there are the plethora of additives, such as emulsifiers, artificial sweeteners and other flavourings, which are said to destroy the healthy bacteria in our gut – which can protect against disease – and interfere with natural hunger signals, making us eat when we’re full.
But until recently, the supposed harms to the brain were relatively unknown. The bulk of the research in this area was what’s known as observational – where scientists track the diets in groups of people over a long period and look for patterns in their health outcomes.
A number of studies from France and Italy have shown the more ultra-processed food a person eats, the more likely they are to develop depression and anxiety disorders
A number of studies from France and Italy have shown the more ultra-processed food a person eats, the more likely they are to develop depression and anxiety disorders. However, critics have argued that this evidence is not proof of ultra-processed food’s effect on mental health. They claim it could be the case that poor mental health leads people to seek out fast food.
‘It is very possible that people with depression change their diet and might decide to consume foods that are easier to prepare – which would often be foods considered ultra-processed,’ said Gunter Kuhnle, professor of nutrition and food science at the University of Reading.
But emerging evidence suggests diets high in this type of food do in fact directly impact brain health.
In 2020, a group of international researchers carried out a trial in which 50 adults were asked to eat eight Belgian waffles and two takeaways over the course of a week.
At the end, and once back to their normal diet three weeks later, they completed cognitive assessments to test the area of the brain called the hippocampus which is involved with memory, learning, emotional processing and mood. Their results were compared with another group who ate a typical, nutritious diet. Scientists found that the waffles and takeaway group performed far worse on the tests at the end of the week, and that their results improved significantly once back to their regular diet.
The authors argued that the results suggested that just a small amount of ultra-processed food can impair the hippocampus.
Previous studies have found that those who eat diets high in ultra-processed food were more likely than others to have an unusually small hippocampus.
‘The research is now pointing to structural brain changes as a result of what we do or don’t eat,’ said Kimberley Wilson, a psychologist specialising in nutrition and a co-presenter of the BBC podcast Made Of Stronger Stuff.
Some experts believe the explanation lies in the nutrients missing from most junk food products.
Studies from Brazil and Mexico involving more than 30,000 people have noted that the more junk food a person eats, the more likely they are to be deficient in vitamins and minerals that are vital for brain health
Studies from Brazil and Mexico involving more than 30,000 people have noted that the more junk food a person eats, the more likely they are to be deficient in vitamins and minerals that are vital for brain health. This includes a range of B vitamins found in leafy green vegetables such as kale and spinach, milk and fresh fish.
Research shows that these nutrients, in particular Vitamin B12 and folate, are essential for growing healthy brain cells and protecting them from age-related damage.
A number of trials have shown that giving a combination of B vitamins to older people can reduce the death of brain cells, and even improve scores on memory tests. But there’s also evidence of mood benefits, too. A 2015 trial, published in the British Journal of Psychiatry, showed that combining antidepressants with B12, folate and B6 greatly reduced the risk of relapse after a year compared with taking drugs alone.
Dr Carmine Pariante, professor of biological neuroscience at The Institute of Psychiatry at King’s College London, said that the psychological impact of weight gain caused by ultra-processed food is often underestimated
Another emerging area of research is the impact of ultra-processed food on the trillions of bugs inside the bowel, called the microbiome.
This collection of microscopic bacteria – often labelled ‘good’ or ‘friendly’ bacteria – play a vital role in many bodily processes, including the immune system, the gut and, increasing numbers of studies show, mental health. It is thought certain bacteria interact with enzymes in our food, releasing chemicals that send stress-relieving signals to the brain.
Dr James Kinross, a consultant colorectal surgeon at Imperial College London, highlighted the role of the vagus nerve, which connects the gut and brain and is involved in physical feelings of fear and anxiety.
‘Studies show the microbiome can influence how well the vagus nerve functions,’ he said. ‘If it operates erratically, there’s interference in the signals which could lead to increased feelings of anxiety.’
Over the past decade, scientists have identified foods that fuel our microbiome, as well as those that kill them off. Experts say some foods interact with gut bugs to generate inflammatory chemicals – substances that send the immune system into ‘attack’ mode.
‘The immune system releases harmful proteins which weaken the barrier between the brain and the body,’ Ms Wilson added. ‘It means pathogens can cross over and affect the brain’s ability to make new connections between cells. Studies show that this is a feature of depression.’
Prof Bullmore also highlighted recent studies by scientists at the University of Auckland in which participants were given a typhoid injection – a safe way to trigger inflammation – and underwent scans of their brains.
‘The people who had the inflammation showed a big spike in activity in brain areas associated with depression and anxiety,’ he said.
Foods that are known to benefit healthy gut bacteria are high in fibre and naturally fermented – such as fruits, vegetables, oats, pulses, including chickpeas and lentils, and yogurt.
‘If there is one, simple thing you can do to improve your physical and mental health, it’s to eat more fibre,’ Dr Kinross said.
He added that eating an extra seven grams of fibre per day (the equivalent of two large bananas) has been shown to improve mental health. It’s estimated that only about one in ten UK adults get their daily recommended intake of 30g of fibre.
Other experts have highlighted less complex, yet equally powerful, reasons why junk food affects our emotional health.
Dr Carmine Pariante, professor of biological neuroscience at The Institute of Psychiatry at King’s College London, said that the psychological impact of weight gain caused by ultra-processed food is often underestimated.
‘They are made with high quantities of salt, fat and sweeteners or sugar – a combination which stimulates the reward system in the brain, making it hard to stop eating.
‘It means people who eat diets high in ultra-processed food are more likely to gain weight easily, which can lead to issues with body confidence. The more someone feels unhappy about how they look, the more they may seek comfort in food, creating a vicious cycle.’
Dr Pariante added that more work needs to be done before we can be ‘100 per cent sure’ that ultra-processed food causes mental illness, though.
‘But a lot of different types of studies appear to be pointing in the same way,’ he accepted.
‘It is clear that if people eat more fresh, healthy ingredients, they experience fewer mental health issues.
‘But exactly how or why? That’s one question we’re very far from finding an answer to.’
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