Can stomach bacteria make you dumber?

  • Can Stomach Bacteria Make You Dumber?
  • Can Stomach Bacteria Make You Dumber?

Can Stomach Bacteria Make You Dumber?

  • By Sarah Lang
  • Dec 18, 2018

We revisit this 2017 interview with gut guru Dr Michael Mosley, ahead of his 2019 talk in New Zealand.

Can Stomach Bacteria Make You Dumber?

There really is a second brain in your gut – and you can make it work smarter, says Dr Michael Mosley. He says improving intestinal health can help you lose weight, boost your immune system, lower the risk of type 2 diabetes, and even lessen anxiety and depression. Sarah Lang reports.

On one summer morning in 2012, Dr Michael Mosley – the award-winning British television journalist, producer and presenter of programmes on biology and medicine – strolled into London’s Science Museum to film a segment for a BBC special.

Overseen by a gastroenterologist, Mosley swallowed a centimetre-long capsule, which contained a tiny camera that takes pictures of the gastrointestinal tract (a procedure known as a capsule endoscopy). The “pillcam” was linked to a screen that broadcast images of Mosley’s gut in action to their human host and a live audience.

This journey through his insides is threaded through Mosley’s just-released book The Clever Guts Diet: How To Revolutionise Your Body From The Inside Out (Simon & Schuster, $35). No dry scientific tome, it’s a funny, fascinating tour of the gut – and the 30-50 trillion microbes (mainly bacteria) that live there and make up your microbiome.

Watch Michael Mosley predicting New Zealand's next health trend:

The ancient Greek physician Hippocrates said all disease begins in the gut; it just took a while to figure out he was on to something. More than 2400 years later, humans have reached a new frontier of gut science, thanks largely to the genetic revolution enabling scientists to identify bacteria by looking for fragments of their DNA, and the introduction of the pillcam.

It's still early days, but already strong evidence is emerging that the microbiome is responsible for a lot more than we thought.

As Mosley outlines, research indicates that improving your gut health can help you lose weight, boost your immune system, reduce the impact of common conditions such as irritable bowel syndrome (IBS), and even lessen anxiety and depression.

The study of the gut-brain axis now has its own name, psychobiotics, and some scientists have even proposed classifying the microbiome as a distinct organ.

Where there’s a gut, there’s poo. In Europe, trials are under way to determine whether gut microbiome transfer (usually called faecal transplants) can treat obesity and diabetes by repopulating participants’ guts with good bacteria.

Here in New Zealand, scientists at the University of Auckland’s Liggins Institute are giving 80 overweight teens capsules that contain gut bacteria from lean donors.

Preliminary results from the Gut Bugs Trial’s pilot study are expected later this year.

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All this research is aiding understanding of how our bodies work – and how we can help them work better. Rather than waiting for the information to disseminate slowly, Mosley wants to help readers slot the science into their lives right now, whether they have gut conditions or simply want to improve their gut health.

The Clever Guts Diet details helpful foods and those to avoid, with some surprises on the lists. And it clears up any confusion about what does and doesn’t constitute prebiotics (non-digestible plant fibre that encourages the growth of “good” bacteria) and probiotics (live bacteria that parachute into your intestines).

This is also a recipe book, with dishes devised by nutritional therapist Tanya Borowski and Mosley’s GP wife Clare Bailey.

Borowski’s two-stage remove-and-repair programme for people with mild gut conditions outlines how to eliminate then reintroduce foods to see if symptoms improve, and Mosley also examines how exercise, sleep and stress interlink with your microbiome, and the damage wrought by antibiotic overuse.

We caught up with him the week his book became a UK bestseller and the accompanying website went live.

Can Stomach Bacteria Make You Dumber?

North & South: Tell me more about swallowing a pill camera at the Science Museum for a big-screen odyssey through your insides. (video below).

Michael Mosley: It was one of the most interesting and informative experiences of my life. I fasted and took some vile-tasting laxatives so the camera would get a clear view.

When the camera got stuck at the bend where the oesophagus meets the stomach, I got a bit panicked that I’d have to go into surgery.

But the gastroenterologist with me said, “Jump up and down, it’ll go through,” so I did and it did.

The audience was partly enthralled, partly disgusted, but I was fascinated. My stomach reminded me of the surface of Mars, while my small intestine reminded me of snorkelling in a bay full of seaweed. Eight hours after I swallowed it, the camera made it to my large intestine, home to the microbiome. Twenty hours after I swallowed it, the camera ended its journey in my toilet.

N&S: Where is it now?                 MM: By my bedside in a little box. I hand it around at talks sometimes. Well-cleaned up, I promise.

N&S: You’ve never heard anyone say they want to dedicate their life to the unglamorous gut. Are you suggesting that poo’s “ew” factor is one reason why research in this field has been neglected until recently? MM:

The Fundamental Link Between Body Weight and the Immune System

Edgar Su / Reuters

It’s simple: Eat less.

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Sometimes combined with the directive move more, this mantra has a clear point. If you can’t lose weight, you are either stupid or lazy—or, probably, both. See also: Calories in, calories out.

But if things were that simple, diets would work. Middle-aged people would not suddenly start gaining weight despite eating and moving similarly year after year.

No one would have to endure the presence of that one friend with the “fast metabolism” who can eat anything he wants.

And who, even though he knows you’re on a diet, says through his overstuffed mouth, “I couldn’t even gain weight if I tried.”

Instead, it is becoming clear that some people’s guts are simply more efficient than others’ at extracting calories from food. When two people eat the same 3,000-calorie pizza, for example, their bodies absorb different amounts of energy. And those calorie-converting abilities can change over a person’s lifetime with age and other variables.

The question is, why? And is it possible to make changes, if a person wanted to?

If so, the solution will involve the trillions of microbes in our intestines and how they work in concert with another variable that’s just beginning to get attention. The immune system determines levels of inflammation in the gut that are constantly shaping the way we digest food—how many calories get absorbed, and how many nutrients simply pass through.

The relationship between microbes and weight gain has long been overlooked in humans, but people have known about similar effects in animals for decades.

After World War II, antibiotics became affordable and abundant for the first time.

Farmers began giving the drugs to their livestock—for example, to treat a milk cow’s infected udder—and noticed that animals who got antibiotics grew larger and more quickly.

This led to a flood of patent applications for antibiotic-laden foods for all sorts of livestock. In 1950, the drug company Merck filed a patent for “a method of accelerating the growth of animals” with “a novel growth-promoting factor” that was, simply, penicillin.

Eli Lilly patented three new antibiotics to mix into the feed of sheep, goats, and cattle because the microbe-killing agents “increased feed efficiency.

” In the ensuing decades it became standard practice to give livestock copious doses of antibiotics to make them grow faster and larger, even though no one knew why this happened, or what other effects the practice might have.

Read: Are antibiotics making people larger?

Researchers have only recently shown that these antibiotics kill off some of the microbes that occur normally in the gut and help livestock, and people, digest food. By breaking down nutrients and helping them pass through the walls of the bowel, these microbes serve as a sort of gatekeeper between what is eaten and what actually makes it into the body.

Killing them is not without consequences. Just as antibiotics are associated with faster growth in cattle, a decrease in diversity in the human microbiome is associated with obesity. As the usage of animal antibiotics exploded in the 20th century, so too did usage in humans.

The rise coincides with the obesity epidemic. This could be a spurious correlation, of course—lots of things have been on the rise since the ’50s.

But dismissing it entirely would require ignoring a growing body of evidence that our metabolic health is inseparable from the health of our gut microbes.

In 2006, Jeffrey Gordon, a biologist at Washington University in St. Louis, reported that the microbiomes of obese mice had something in common: Compared with their lean counterparts, the heavier mice had fewer Bacteroides and more Firmicutes species in their guts.

What’s more, biochemical analyses showed that this ratio made the microbes better at “energy harvest”—essentially, extracting calories from food and passing it into the body. That is, even when mice ate the same amount and type of food, the bacterial populations meant that some developed metabolic problems, while others didn’t.

Similar bacterial patterns have since been confirmed in obese humans.

What’s more, Gordon found, the microbiome associated with obesity is transferable. In 2013, his lab took gut bacteria from pairs of human twins in which only one twin was obese, then fed the samples to mice. The mice given bacteria from the obese humans quickly gained weight. The others did not.

Giulia Enders on what your gut really thinks of you

Enders was plagued by skin problems in her teens. “If I had known more about the gut back then,” she writes, “I could have placed bets on what illnesses I would contract in later life.”Credit:Gordon Welters

I was determined not to fall into the same trap, but we have only gone two blocks when the subject of constipation comes up. Enders is about to fly to Australia and we agree that long-haul travel can play havoc with the insides.

She was recently invited to talk to crew members of Lufthansa, the national airline, and asked how they were affected by the eating and sleeping patterns of frequent flying. There was a chorus of voices. “Everyone wanted to talk about it,” she says.

“For example, it's common to suppress the urge to 'go' in certain places or at inconvenient times, so the bowels go into reverse gear.”

Is she plagued by people wanting to discuss their grumbling tummies or irritable bowels? “Oh, I love this,” she says happily. “At parties, I find myself talking to people I wouldn't normally have anything in common with.

” During her year of hospital training in Karlsruhe, patients were at first embarrassed to talk about their intestinal problems, she says: “They speak in whispers, but I tell them that the gut is an organ being busy and responsible – not something to be ashamed of.”

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We cross a small park encircled by art nouveau buildings – the only bit of prewar Mannheim left standing – through a doorway hung with velvet curtains into a softly lit cafe of brass, plush and mahogany, and choose a quiet corner table.

Enders tells me that her interest in the gut began when she was 17 and troubled by weeping sores on her legs, arms and back. Several visits to doctors produced little help beyond a prescription for cortisone.

“I thought, 'What is my immune system fighting?' So I did some research.”

Do Parasites Make You Dumber?

What can you do to make your kids smarter? Keeping them healthy might help. A new study suggests that worldwide differences in intelligence can be explained by disparities in infectious disease.

The researchers found that countries most heavily affected by infectious diseases generally had the lowest average IQs.

They propose that these illnesses hinder children's brain development, though their conclusion is gathering mixed reviews.

The new research relies on data first published in 2002 in a controversial book called IQ and the Wealth of Nations.

In the book, psychologist Richard Lynn of the University of Ulster in the United Kingdom and political scientist Tatu Vanhanen of the University of Tampere in Finland searched the published literature to come up with measures of average IQ for 81 countries. They also estimated IQ for another 104 countries by averaging the IQs of nearby nations.

Hong Kong topped the list, with an average IQ of 107. The authors argued that national differences in IQ at least partly explained differences in national wealth. In 2006, they expanded the data to include IQ measurements from 113 countries and new estimates for 79 more.

Several groups have attempted to explain the pattern. In the new study, Christopher Eppig, a Ph.D. candidate in biology at the University of New Mexico, Albuquerque, and his colleagues propose that low IQ is tied to the toll of infectious diseases.

Their idea, which the researchers call the “parasite-stress hypothesis,” is that children who contract “parasites,” which they define to include everything from intestinal worms to bacteria and viruses, devote more energy to fighting off infection. As a result, they have less energy available for brain development.

Countries where infectious diseases are prevalent, Eppig and colleagues argue, will have lower intelligence.

To test this idea, the researchers statistically analyzed the relationship between Lynn and Vanhanen's 2006 data and 2004 data on infectious disease burden from the World Health Organization, which measures potential years of healthy life lost to premature death and illness as a result of 28 infectious diseases, including malaria, hepatitis, and tetanus. The researchers also reexamined factors that other research groups had linked to IQ, such as nutrition, literacy, education, gross domestic product, and temperature.

The numbers seem to support the hypothesis, the team will report online tomorrow in the Proceedings of the Royal Society B.

When the researchers analyzed each factor independently, they found that infectious disease burden was more closely correlated to average IQ than the other variables. “Parasites alone account for 67% of the worldwide variation in intelligence,” Eppig says.

To further assess the relationship, the researchers built a statistical model that allowed them to test the predictive power of infectious disease burden against other variables previously associated with IQ, such as education, temperature, distance from sub-Saharan Africa, and wealth. Infectious disease burden again came out on top, although temperature and distance from sub-Saharan Africa explained some of the variation as well.

Eppig points out that their study can't rule out any of the other factors. “I would never say that parasites are the only thing affecting the global diversity of intelligence.”

Maureen Black, a pediatric psychologist at the University of Maryland School of Medicine in Baltimore, is skeptical. She argues that health by itself isn't enough for full brain development.

“For children to develop intellectual skills, they need not only strong bodies and the absence of infections, they also need opportunities to explore and opportunities for enrichment.

” Those opportunities might be lacking in countries with low average IQ.

But Richard Guerrant, a physician and infectious disease expert at the University of Virginia School of Medicine in Charlottesville, says the researchers are on the right track. His work suggests a link between diarrheal diseases, malnutrition, stunted growth, and lower IQs. The next challenge, he says, will be to uncover the exact mechanisms.

Is your gut making you sick?

A gut full of diverse microbes – bacteria, viruses and fungi – is essential for a healthy mind and body. And evidence is growing that our modern diet, overuse of antibiotics and obsession with cleanliness are damaging the diversity of microbes that live in our guts, contributing to a range of conditions including depression, multiple sclerosis, obesity and rheumatoid arthritis.

Microbes live in our guts, bodily fluids, cavities and skin. For every one of our human cells, there’s at least one of them. In an average adult, they weigh in at 1-2kg; similar to our brain.

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Collectively, they’re called the human microbiota and their genes are the microbiome. Only a few microbes cause disease; most are beneficial and live in peaceful symbiotic coexistence in and on our bodies. We need them and they need us.

And if our microbes aren’t healthy, neither are we.

Microbiome and the diet

A healthy microbiome protects against obesity, allergies and diseases as bacteria break down food in the colon, providing energy for themselves and useful byproducts for us. These byproducts are essential components of chemicals that affect mood, appetite, metabolism, inflammation and the immune system.

Professor Tim Spector of King’s College London says that variations in the gut microbiome explain, in large part, why our kids are getting fatter and why some individuals gain more weight than others on the same diet.

There is no good evidence that we consume more calories or do much less than previous generations, yet people around the world are getting fatter, and Spector says that, while genetics play a part, so does the diversity and types of microbes in the gut.

The gut microbiome is mostly influenced by diet and environment. Babies get their first exposure to bacteria that colonise their guts as they travel down the birth canal. Babies born by caesarean section, as at least a quarter are in the UK, appear to be more prone to obesity.

Spector explains that a good diet is a diverse one, with a range of fibre and vegetables including artichokes, leeks, onions and garlic.

Polyphenols, found in foods including nuts, seeds, coffee, dark chocolate, red wine, olive oil and berries, are used by microbes as an energy source, with beneficial effects on human immune cells.

Foods that nourish the microbiome are called prebiotics, and foods that contain the actual microbes, such as yoghurt and fermented milk called kefir, are called probiotics. Fermented foods, such as sauerkraut, kimchi and miso, are combinations of probiotics and prebiotics, known as synbiotics.

Inflammatory arthritis

An international consortium of scientists is studying faecal samples from people with inflammatory arthritis, such as rheumatoid arthritis. Bacterial groups that seem to be increased can be isolated and introduced to rodents, triggering the development of arthritis in previously healthy animals.

Professor Michael Dustin of the University of Oxford says that the risk of developing rheumatoid arthritis is associated with genetic predisposition and environmental factors. “But it’s much easier to modify your microbiota than change your genes,” he says.

Tests for rheumatoid arthritis can prove positive several years before symptoms appear, so there’s a window of opportunity to try to stave off the onset of the condition. Using that time to establish a more protective microbiota is one approach being studied.

Dustin says that we still don’t know whether dietary changes are enough or whether more radical procedures (such as faecal transplants) are necessary.

Variations in the gut microbiome explain why our kids are getting fatter and why some individuals gain more weight

Tim Spector, King’s College London


Changes in the gut microbiome can be very dangerous; people treated with prolonged courses of antibiotics that kill a wide spectrum of bacteria can develop life-threatening diarrhoea due to an overgrowth of Clostridium difficile.

Faecal transplants (infusions of donor faeces down a nasal tube or up the rectum into the gut) are used to treat these extremely unwell patients, proving that disruption of the gut microbiome can cause serious illness and restoring it to normal can cure the problem.

Multiple sclerosis

About 100,000 people in the UK live with multiple sclerosis (MS), a neurological condition that can cause problems with vision, balance, sensation and movement. Researchers have found specific changes in the microbiome of people with MS that appear to be linked to changes in their immune function. And drug treatment of MS has also been shown to impact on the gut microbiome.

Dr David Schley of the MS Society says: “The link between MS and the bacteria living in our intestines is an exciting area of research. Recent studies in mice have indicated that intestinal microbes could influence symptoms.

While this early evidence is intriguing, we need to learn more before we can make recommendations over whether people with MS should make changes to their lifestyle or diet.”


According to the World Health Organisation, depression is the leading cause of disability worldwide. So, there is a lot of interest in the role of the gut microbiome in preventing and treating it.

Professor John Cryan of University College Cork says: “We now know that good brain health depends on good gut health. The gut microbiome affects every aspect of brain functioning and human behaviour.

” Studies have shown that rats with high levels of bifidobacteria in the gut withstand psychological stress better than those with low levels.

And it appears that humans do, too; recent human studies from the Cork group in healthy volunteers show increased brain activity (measured by EEG) and reduced levels of stress (measured by rating scales of anxiety and chemicals in the blood, such as cortisol, that rise in response to stress) when people are given demanding tasks to perform.

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