DR MICHAEL MOSLEY: How ‘bad’ gut bacteria could make you mean and aggressive

You are what you eat is far from a new idea. But would you be surprised to learn that there’s a link between our diet and how aggressive we are? And that supplementing prisoners’ food with vitamins and minerals has been shown to reduce violence and bad behaviour?

The idea that a poor diet can make people more aggressive is not strictly new, either.

Back in the 1940s a maverick scientist called Dr Hugh Sinclair (who was one of the first people to prove the health benefits of eating oily fish) was urging the wartime British government to give children free cod-liver oil and orange juice, on the grounds that, among other things, a poor diet can lead to antisocial behaviour.

I also remember reading a book in the 1970s, called Nutrition And Your Mind, by U.S. psychologist Dr George Watson, where he argued that if you get people to eat more nutrient-dense, fibre-rich foods and more ‘good’ bacteria (in the form of yoghurt), this will improve not only their gut health but also their behaviour.

People didn’t know much about gut bacteria back in the 1970s, so he was clearly ahead of his time.

These claims — that you could improve people’s behaviour by changing their diet — were largely ignored until researchers at the University of Oxford decided, in 1998, to carry out a nutrition study in a nearby prison.

At the time, prisoners were fed on a cheap and starchy diet, consisting largely of cereal, white bread and ultra-processed foods such as mass-produced meat pies. (According to a friend of mine, who works in a prison, little has changed in prison catering.)

For the study, the Oxford researchers randomly allocated 231 male prisoners either to taking a pill containing vitamins, minerals and omega 3 (a fatty acid that you mainly get from consuming oily fish), or a placebo.

Neither group knew what they were taking and both groups took their pills every day for just over four months.

During this time, the researchers tracked the prisoners’ behaviour through ‘the Governor reports’, which are records of any acts involving intimidation or violence.

At the end of the study, which was published in the British Journal of Psychiatry in 2002, the researchers found there had been a remarkable 37 per cent reduction in reports of violence in the group getting the supplements, while there was no significant change in the behaviour of the prisoners taking the placebo.

A similar study was later carried out by California State University in the U.S. in 2021, with 450 young offenders, who were given a vitamin and mineral supplement, with added omega 3 — this led to a 39 per cent reduction in violent attacks on staff and other prisoners.

The researchers pointed out that since committing violent actions leads to more time in prison, as well as higher levels of sick leave and more burnout among prison staff, giving prisoners supplements would be a cost-effective way to not only reduce levels of aggression in prisons, but also save money (according to the Ministry of Justice, it costs more than £47,000 a year to house a single prisoner — so spending a small amount on improving their nutrition seems to me to be a good investment).

And, of course, it’s not just prisoners. A study of aggressive children, aged 11 to 12 years old, by the University of Pittsburgh in 2016 showed that three months of taking supplements containing vitamins, minerals and omega 3 led to a significant fall in aggressive behaviour. Sadly, when the children stopped taking the supplements, the bad behaviour returned. So why does taking supplements have this effect?

Well, anyone who is eating a largely junk food diet is almost certainly deficient in key nutrients, and we know from numerous studies that getting an adequate supply of the right vitamins and minerals, throughout your life, is essential for the proper functioning of your brain and central nervous system.

And that, in turn, can have a big effect on impulse control, where you are able to control your feelings of anger and aggression.

There is also the impact that a poor diet has on your gut microbiome — the microbes that live in our gut and that influence our health in so many different ways.

In a recent study involving mice, which is yet to be published, scientists at Bar-Ilan University in Israel showed they could make mice more or less aggressive simply by manipulating their microbiome. The less diverse their microbiome, and the more ‘bad’ bugs they were harbouring, the more aggressively the mice behaved.

It’s not clear why, but it could be because the bad bugs produce chemicals that cause inflammation, and those chemicals can travel to the brain via our blood supply.

Conversely, if you are harbouring a lot of ‘good’ bugs in your gut, they help produce feel-good hormones such as dopamine.

On top of that, the scientists showed that changing the mice’s microbiome led to the switching on, or off, of genes linked to aggression in their brains.

I am not sure any of this means we can say ‘it wasn’t my fault, my gut bacteria made me do it’ — but there seems little doubt that looking after your gut bacteria could help keep mood levels steady.

You know the drill: eat a healthy, Mediterranean-style diet with lots of vegetables, nuts and oily fish, and include fermented food such as sauerkraut and yoghurt.

It may feel like ages ago, but when you were on the beach last summer enjoying the sun, what was actually happening is that your body was busy producing melanin, a chemical that protects our skin against the sun’s UV light. Now researchers at Northwestern University have developed a cream that contains a synthetic version of melanin, which not only protects skin against sun damage, but also heals skin already damaged by the sun or chemical burns.

The hope is that in future, it could be used in sun lotions and for patients about to undergo radiation therapy.

The future for donor patients?

I’ve long been fascinated by the range of things that surgeons can transplant — I’ve filmed people having kidney transplants, heart transplants, lung transplants and even a hand transplant.

The latter was particularly strange because the donor arm, which was grafted on to a man, actually came from a woman; and because it was a different size, it looked out of place. But the main thing is it worked.

So I was excited to read in the Mail that Aaron James, a U.S. veteran, has recently had the world’s first whole eye transplant, along with a partial face transplant, after surviving a 7,200‑volt electric shock.

The major drawback with transplants is that you normally have to take immune-suppressing drugs for life, and these have significant side-effects. So much so that one patient who had an arm transplant gave up taking the drugs after three years and lost the arm.

But this may all change: in a recent study by the University of Pittsburgh in the U.S., patients about to undergo a liver transplant were infused with dendritic cells from the donor. Dendritic cells roam your body, identifying anything they think is ‘foreign’, flagging it up to the immune system to destroy it.

But adding dendritic cells before the liver transplant ‘taught’ the recipient’s immune system to tolerate the new organ, so immune-suppressing drugs were not needed.

If further trials are successful, this could revolutionise transplants.

Embrace the cold to live longer

How old are you really? Not how many birthdays you’ve had, but deep down, at the cellular level?

As part of a recent series I made about super-agers (people in their 70s and over who look and act decades younger) I went to the Clock Foundation in California, where they’re doing cutting-edge research into longevity.

They’ve developed a biological age test — based on work by the University of California, Los Angeles — that measures certain chemical changes in DNA that happen over time. The test is also known as the ‘Death Clock’, because it’s a far better predictor of how long you have left than the number of candles on your birthday cake. To my relief, the test showed that although I’m 66, my biological age is only 61.

Being biologically younger than your age can make a difference: new research published in the Journal of Neurology, Neurosurgery and Psychiatry found that if your biological age is five years higher than your real age, you have a 40 per cent higher risk of developing dementia or a stroke.

But you can reduce your biological age. Studies suggest doing more exercise, good quality sleep and a healthy microbiome all help — as may mild hypothermia (i.e. being cold). So that’s one good thing as we face the cold months ahead.