Parkinson’s disease, autism and depression – could diet be the cause of these and other supposed diseases of the brain?
An increasingly compelling body of scientific research suggests it is.
Numerous studies into the branch of the nervous system that lies in the gut – the enteric nervous system (ENS) – indicate that, contrary to popular belief, mood and behaviour disorders don’t necessarily originate in the brain. While the ENS regularly communicates with the brain to regulate things like appetite, alteration of the gut environment can distort this communication and result in mood and behaviour disorders.
This may explain the puzzling gut symptoms known to occur in patients with neurological diseases and vice versa. For example, patients with Parkinson’s disease often report constipation and bowel-related symptoms up to 10 years before the familiar motor deterioration symptoms of Parkinson’s disease begin. And reports from the US have stated that somewhere between 50% and 90% of irritable bowel syndrome (IBS) patients who seek treatment also have a psychiatric disorder, such as anxiety or depression.
So, how does it work? Is it what, when or how much you eat that causes the type of gut dysfunction that triggers brain-related conditions? To find the answer, we have to look deep inside the intestine and explore something known as the gut microbiota.
Influence of the gut microbiota on health
The gut microbiota is the collective term for the 100 trillion plus microorganisms that live in the bowels. These organisms include fungi and bacteria and are involved in maintaining normal metabolism, absorption of nutrients and immune function. Disruption of the delicately balanced gut microbiota – either through an excess or lack of important microorganisms – is known to result in gastrointestinal conditions, such as inflammatory bowel disease.
Disruption of the delicately balanced gut microbiota – either through an excess or lack of important microorganisms – is known to result in gastrointestinal conditions, such as inflammatory bowel disease.
But that’s not all.
It now appears that upsetting the gut microbiota has repercussions far beyond the bowels.
Scientists have long known that the intestinal microbiota and the substances it produces (known as metabolites) directly affect the gut’s ability to function properly. A loss or excess growth of bowel bacteria and fungi can affect intestinal permeability, how easily nutrients are absorbed into the body and normal bowel movements. This is why bowel conditions like IBS often develop after food poisoning or other gut infections that upset the balance of normal gut bacteria, fungi or viruses.
Recent studies, however, have shown that the gut microbiota and its metabolites alter ENS activity, which in turn changes normal behaviour and brain activity. This is achieved via neurotransmitters – chemicals released by nerve cells to relay important information between the nervous system and other cells of the body.
How the gut communicates with the brain
You may be familiar with the hormone serotonin. It’s a neurotransmitter that your brain releases after activities such as eating chocolate or laughing. That’s why doing these things feels so good. But did you know that scientists now believe 95% of serotonin is made in the gut, not the brain?
According to research carried out in the US, serotonin is produced by a special type of nerve cell found in the gut, called an enterochromaffin (EC) cell. The main function of this serotonin is to alter ENS activity. What is really interesting is that the amount of serotonin made by EC cells is dependent on the balance of the gut microbiota. When the researchers looked at the activity of mouse EC cells, they found that mice that lacked normal gut microbes made 60% less intestinal serotonin than those with normal levels of gut bacteria.
But serotonin is not the only neurotransmitter that’s dependent on gut bacteria. Research published this year showed that the common gut bacteria species Lactobacillus and Bifidobacterium produce gamma-amino butyric acid (GABA), a neurotransmitter that’s known for calming anxiety. Lactobacillus has long been known to produce acetylcholine – the neurotransmitter responsible for making us feel alert. And according to one neuroactive gut bacteria expert, Bacillus and Serratia bacteria species produce dopamine – the hormone that motivates us to do rewarding things.
It’s not just the production of neurotransmitters within the gut that links the intestinal microbiota and the brain; there’s also the role of immune cells. Your gut has an extensive immune system that protects your body against infection, inflammation and damage. When foreign organisms invade the body, the cells of the immune system (both in the gut and elsewhere) release substances to start the fight against the infection. Numerous studies have linked a group of molecules involved in the immune response process, called inflammatory cytokines, to the development of depression.
Numerous studies have linked a group of molecules involved in the immune response process, called inflammatory cytokines, to the development of depression.
How antibiotics can upset gut balance
As an advocate of restorative medicine, my focus is on teaching people how to maintain a well-balanced gut microbiota. The link between gut microbiota and brain function lends further weight to the argument for being careful what you consume. The gut does a great job of balancing its levels of the bacteria and fungi that keep it working as it should, but this fine balance can be easily upset by eating and drinking things that kill off gut microorganisms.
And that includes medicines, specifically antibiotics.
While these drugs are effective for treating infections, recent data from the US suggests that antibiotic misuse is rife. It notes that a staggering one in three antibiotic prescriptions issued in the States is completely unnecessary. This is a problem in the UAE too, as revealed by a 2016 exposé which found that many pharmacies here dispense antibiotics to patients without prescriptions – contrary to the advice of the Ministry of Health.
It’s not just pharmacists who appear to be contributing to unnecessary antibiotic use in the UAE either. A 2012 study showed that many doctors in the UAE still incorrectly prescribe antibiotics for colds and sore throats.
Take these drugs too often or for long periods of time and they can kill off the strains of bacteria the gut needs to function at its best. If you want to maintain a healthy gut, step number one is to avoid unnecessary antibiotic use. For example, there’s no need to take an antibiotic if you have a cold because the common cold is caused by a virus not a bacteria, so antibiotics won’t help.
When you do require antibiotics for a bacterial infection, you can prevent them from wiping out your protective gut bacteria by topping up your levels of ‘good’ bacteria with a probiotic supplement or natural foods like ‘live’ yoghurt, kefir and pickled vegetables. While the health benefits of probiotics remain contentious among the scientific community, the one probiotic benefit on which there is a consensus of agreement is the protection of the gut during antibiotic treatment.
What constitutes a gut-friendly diet?
Eating a gut-friendly diet is another way to maintain a healthy gut microbiota. This starts with minimising your intake of the sugary foods and refined/processed carbohydrates that encourage the growth of ‘bad’ gut microorganisms, like Candida albicans. Candida is a type of yeast (a fungus that feeds on sugar) found in the gut microbiota in small amounts. A little of it is necessary for healthy digestion but too much can damage the gut wall, allowing the fungus to enter the bloodstream and cause widespread infection. This excess of yeast gives us chronic fatigue, sugar cravings and a desire to reach for pick-me-up food rich with refined carbs.
So cut out the processed carbs and sugar if you want to maintain optimal gut health (and get your carbs from healthier sources such as vegetables, fruits, nuts and seeds). And watch your alcohol intake too. In 2015, researchers found that drinking too much alcohol, too often, can disrupt the balance of the gut microbiota, make the gut leaky and encourage the production of inflammatory chemicals called endotoxins.
Cut out the processed carbs and sugar if you want to maintain optimal gut health (and get your carbs from healthier sources such as vegetables, fruits, nuts and seeds). And watch your alcohol intake too.
The science is clear: what you eat really can impact on your overall health, mood and mental wellbeing by altering the way your gut’s microorganisms ‘talk’ to your brain. The good news is that you can take control of your gut health today without any need for medication or a complicated treatment plan.
Simply cut out the processed sugary foods, alcohol and other villains of the Western diet, and add natural probiotics into your daily routine. And don’t forget to prioritise getting a good night’s sleep.