Food for thought: How your belly controls your brain

Ruairi Robertson |  Dec 2015

2024년 4월 18일 shadowing 완료

 

 

 

 

TED Talker/연자

Ruairi Robertson
Assistant Professor and Group Leader in Microbiome Science at the Blizard Institute, Queen Mary University of London

Imagine this: You have just won $10 million in the lottery. Congratulations. You have just eaten the most delicious, warm, chocolate brownie that has ever been baked.  You have just had sex. And you have just done all three at the same time. Congratulations to you, too. In these situations, our brains produce chemicals called neurotransmitters which give us these great feelings of energy, excitement and happiness. And without such chemicals inside of us, we wouldn’t feel such emotions during such pleasant circumstances. So instead, imagine this: You’ve just been fired. You’re about to sit an exam. You have depression. In these situations, our brains, instead, produce different chemicals, making us feel stressed and anxious. The highs and lows of life are controlled by our emotions and these chemicals in our brains. This vital organ inside all of us that controls everything that we feel, think and do. However, as a biologist, I’ve always found it strange to comprehend that every feeling, thought, and action that we have is controlled by a three-pound, soggy lump of cells inside of our heads, until I discovered that this might not be the case.

The story I want to share with you today unfolds a fascinating new revelation in our understanding of human physiology, that we each have a second brain — another organ in our body which controls as much of our physical and mental functions as the brain in our heads, and which may be the key link between modern disease epidemics, globally, from obesity to cardiovascular disease, maybe even to mental health.

But first, to give you a little introduction to this story, I want to tell you a little bit about my background. I was brought up in a family of psychologists. My mom is a clinical psychologist; my dad a professor of psychology in a university; my sister even has a PhD in psychology. So when it came to me going to university, I wanted to study something different. I’d heard enough about the brain and how it worked at home, so I wanted to study something new. I considered what I was interested in, and I figured out that from a very early age, I’d had a big interest in food. I loved eating food. And so, I decided to study human nutrition. And this was great because I got to study food, how it affected our bodies, how it could contribute to disease, and more importantly, how we could use it to fight and prevent disease. 

This story begins back in 1845 with the birth of a curious young boy in Russia who became an incredible man, but who was forgotten by history and medicine. Ilya Mechnikov was fascinated by everything in nature, and by the age of eight, he was taking notes on all the living things in his vibrant back garden. He became so good at science that he discovered the role of phagocytes, some crucial cells in our immune systems, for which he won the Nobel Prize in 1908. But it was his science after winning the Nobel Prize that was even more crucial to our understanding of human health, through a tale of discovery, death, and self-experimentation. 

See, everyone in this room has something in common. We all spent the first nine months of our existence inside our mothers’ wombs. And this was essentially a sterile environment where no other living things existed, just you. But as you emerged into this world, you were smothered in an invisible coating of microbes, friendly microbes from your mother’s birth canal. And these bacteria grew to form what is now a three-pound invisible organ inside your large intestine, the same weight as your brain, and which has become known as our microbiota, or microbiome.  And this invisible organ has grown so much, in fact, that right now, 90% of the cells in your body are bacterial cells; only 10% are your own human cells. So you are more bacteria than you are human. This ecosystem of microbes in your gut is as diverse as the Amazon rainforest. Thousands of species all with different functions. And your health is incredibly dependent upon the life and vibrancy of this rainforest. Your gut bacteria digest certain foods, produce essential vitamins and hormones, respond to medicine and infections, control your blood sugar and blood cholesterol levels.Meaning the types of bacteria in your intestines can significantly control your risk of certain diseases from obesity to diabetes, maybe even osteoporosis. They’re involved in just about every process in your body. They function almost as a second brain. 

Well, Ilya Mechnikov [also written as: Élie Metchnikoff] may have figured this out himself in 1892. He lived in France, in Paris at the time, where a deadly cholera epidemic had broken out with thousands of deaths. Naturally, as a scientist, he decided the best way to study this was to drink a broth of cholera himself. Remarkably, he didn’t get sick. So again, as a true scientist, he needed to increase his sample size, so he recruited a colleague to do the same thing. This guy didn’t get sick either. But when he recruited another colleague to do the same, this poor guy got critically ill and very nearly died. By studying cholera under the microscope, Mechnikov found that certain species of bacteria from the human intestines supported and stimulated cholera’s growth, while other species prevented it. He subsequently claimed that our gut microbiota, or our gut bacteria, were essential for human health, and that the right balance of microbes inside of us could help stave off disease. However, popular understanding at the time, was that the human gut was a noxious reservoir of toxins. Surgeons had even begun removing entire sections of human intestines in patients with gut discomfort. Mechnikov’s death in 1916 meant that his ideas that our gut bacteria were good for us were forgotten. 

A decade later, antibiotics were discovered, and drastically became overused. C-sections became common. Diets became Westernized. A war was waged on microbes and we spent a century trying to kill them, which turned our intestinal rainforests into barren wastelands. This Nobel Prize winner’s ideas were lost in time. Some of the implications of this were identified recently. See, right now, one in three children in America are born by C-section, meaning they don’t get this initial inoculum or coating of bacteria that’s been designed by evolution to be in the mother’s birth canal. Instead, they’re first coated with other bacteria on the skin or in the hospital environment which has contributed to up to a 25% increased risk of obesity, asthma, immune deficiencies and inflammatory bowel disease in later life. 

Fortunately, in recent times, we’ve realized we must restore our relationship with gut microbes for our own physical health. However yet, we’ve still completely underestimated their role as our second brains. And this is something that I’m researching. And I learned this first through the intriguing story of a mouse. If mice become colonized by the microbe Toxoplasma gondii, an intriguing thing happens: they lose their fear of cats. In fact, they become attracted to cats. In essence, they go a bit mad, and unfortunately for them, usually end up as dinner for cats. So, this microbe ingested by this animal takes control of its brain, and changes the way that it thinks and behaves. 

So, by delving deep inside the intestinal jungle of bacteria in our intestines, we’ve begun to find some incredible discoveries that are changing our appreciation for bacteria forever. See, our bellies and brains are physically and biochemically connected in a number of ways. First of all, our intestines are physically linked to our brain through the vagus nerve which sends signals in both directions. Interestingly, even though if this is severed, our intestines can still continue to function fully without a connection to the brain, suggesting they have a mind of their own. 
Secondly, our brains are made up of a hundred billion neurons which continuously send messages to tell our bodies how to work and behave. Well, interestingly, our guts have a hundred million neurons. Thirdly, our microbiomes are the center point of our immune systems, meaning a disturbance down here can cause subtle immune reactions all around the body, which if prolonged, can affect brain health.

 

And finally, do we remember our chocolate-eating, lottery-winning womanizer here in the front row? He demonstrated for us the neurotransmitters are these chemicals that can change the way we think and behave, and how we feel. As it turns out, most of these neurotransmitters are also produced in our gut, none more so than serotonin, nature’s antidepressant, 90% of which is produced in our intestines, less than 10% is produced in our brains. Meaning the types of bacteria inside of you may control the way that you think and behave. Has stress ever messed with your insides? Have you ever had a gut feeling? Or butterflies in your stomach? You may have to think twice about that. 

So, as you can see, despite my naive reluctance as a teenager, I’ve begun to study not only one brain, but two brains. In the APC Microbiome Institute in Ireland, we’re fascinated in this link between our belly and our brains, and we research how our modern diets and lifestyles are impacting this gut-brain relationship, and how we can design interventions to target the microbiota in order to prevent and treat chronic diseases.  For example, we’ve shown that the types of fats that you eat throughout life can drastically change the types of bacteria that decide to reside in your intestines. In addition, we’ve shown that by feeding specific strains of bacteria, it can enhance memory, stress behavior, and stress hormone levels in animals. And in addition to a number of other researchers worldwide, we’ve identified lists of foods that can act as prebiotics, or foods that can stimulate the growth of healthy bacteria inside our intestines. To me it’s fascinating that our health is so dependent not only upon nourishing ourselves, but upon feeding other living microorganisms inside of us, meaning future strategies to target and treat chronic diseases, including brain health, may depend on targeting or feeding our gut microbiomes. 

As it turns out, Ilya Mechnikov may have known this himself. See, much earlier in his life he married, but his wife quickly became sick with tuberculosis and died. The stress and trauma of this led Mechnikov to take an overdose of opium. Thankfully, he survived. He then re-married, and when his second wife got sick with the deadly typhoid fever, this time he injected himself with a deadly tick-borne disease. Thankfully, he survived again. It was only after this, Mechnikov began studying and appreciating the microbiota. He moved to Paris to work in the Pasteur Institute where he began hypothesizing that the right balance of microbes in the gut could help stave off disease, and he published a series of books and lectures describing how to achieve this and prolong life. 

Despite the stress and mental turmoil that he’d experienced in earlier life, he spent the rest of his life dedicated and obsessed with researching how to prolong human life. He began studying an interesting group of people in Eastern Europe who were living exceptionally long lives, and he noted that they all drank bacterial-fermented milk every day and he suggested that this contributed to their longevity. Interestingly, he began drinking this bacterial-fermented milk himself, and seemingly lived a healthy life, rid of the stress and mental turmoil he’d experienced in earlier life. Maybe that was just coincidental. He described the time in Paris as the happiest of his life. But Mechnikov died in France in 1916, at the age of 71. The life expectancy in France at the time was 40.

As humans, we all need to adopt a greater appreciation for the microbes inside of us. The incidental war we’ve waged on bacteria over the last century has led to bacterial extinction and sparked an epidemic of modern plagues. I’m here on a Fulbright to research how we can restore our relationship with microbes, and how this can be used to prevent and treat chronic diseases. But I feel that we all have the responsibility and the potential to follow in Ilya Mechnikov’s footsteps. Not only to revive his scientific findings that were lost in time, but to adopt his desire to prolong healthy, human life. Whether it’s by educating ourselves on the risks and benefits of C-sections, restricting unnecessary antibiotic use, or by adopting a gut-friendly diet and lifestyle, we can all support the life of microbes that we’ve evolved to live alongside. 
 
So imagine this: Imagine you’ve just eaten chocolate, or won a lottery, sat an exam or just been fired. Imagine your thoughts, your emotions, your behavior, and your health could be controlled by a hidden organ that you knew little about. Ilya Mechnikov fought to not only prolong healthy human life, but healthy microbial life. I feel we can all contribute to this fight worth fighting for our own health, but more importantly, for future generations’ health, by restoring the relationship between microbe and man. There is some food for thought. Thank you very much.

 

 

Words&phrases/어휘공부

• sit an exam: to take a test or exam
• smother :  to cover most or all of a surface The pasta was smothered with a creamy sauce.
• wage :  to fight a war or organize a series of activities in order to achieve something. wage war on Doesn't the president need Congress' permission to wage war on another country? 
• inoculum : the substance used to make an inoculation
• sever : to end a connection with someone or something. The US severed diplomatic relations with Cuba in 1961 
• stave off : to stop something bad from happening, or to keep an unwanted situation or person away, usually temporarily We were hoping to stave off these difficult decisions until September 
• rid of: to clear, disencumber, or free of something objectionable (usually followed by of): I want to rid the house of mice