The Instagram logo

The second brain

Natural food chef Julie Morris explains the links between gut and brain health

Cognitive function is impacted by all parts of the body, but one system in particular has a very direct effect on it: your gastrointestinal tract, otherwise known as your gut. Often referred to as the “second brain,” your gut is made from the same kind of tissue as your brain (when you develop as a foetus) and is connected to it via the vagus nerve, the long, acetylcholine-activating nerve which runs from your brain stem to your abdomen. The vagus nerve acts like a two-way street – a conduit between your gut and your brain. As a result, the two systems influence each other constantly. For example, you may suffer from tension in your stomach when you’re feeling nervous or experience mental “fogginess” after an unhealthy, hard-to-digest meal. What’s more, the gut is partially responsible for many of your body’s neurotransmitter tasks as well – particularly the production of serotonin.


And this is where the microbiome comes into play. Although it’s true that microbes live everywhere in your body, they are most concentrated and have the greatest diversity in your gut (specifically your large intestine). The health of the microbial ecosystem in your gut plays an important role in many of your body’s functions, including its critical influence on various autoimmune disorders. About one in five Americans currently suffers from these kinds of disorders, which include multiple sclerosis and Parkinson’s disease (both of which cause devastating neurological problems). But believe it or not, around 70 per cent of your body’s immune system is located in your gut microbiome alone. Consequently, an imbalance in this microbiome, which may be affected by anything from stress to illness to medication, can drastically increase the level of inflammatory chemicals that your body is exposed to, causing you to develop chronic inflammation and potentially serious illness over time. Two preliminary studies have shown that mice injected with compromised gut bacteria were significantly more prone to developing brain inflammation and MS-like symptoms than mice that had a healthy microbiome. It’s safe to say that whether or not you develop an illness, your cognitive function will most certainly suffer if your gut is inflamed.

Not surprisingly, the most important factor in keeping your gut healthy comes down to what you put in it. Foods high in sugar, such as whole milk and sugary soda drinks, can attract unwanted bacteria that have a negative impact on the microbial balance of the gut. A 2013 study found that diets rich in animal protein, like meat and cheese, have a dramatically negative effect on gastrointestinal health as well, by promoting the growth of harmful bacteria and causing inflammation. For anyone who is allergic to gluten, glutinous grains like wheat can create a similar problem. Apart from foods, some drugs like antibiotics can have devastating effects on your microbiome balance; these drugs are like little bombs exploding in the healthy world of your gut, and it can take months for your body to recover and replenish the good bacteria it has lost. Consequently, these types of pharmaceuticals, and even antacids, should be taken only when they are truly necessary.

So how can you improve the health of your gut microbiome? Once again, with food! Nourishing your gut flora is extremely important for the health of your body as well as your brain.

Probiotics and prebiotics

Fermented foods have been a part of the culinary traditions of almost every culture in the world, whether in the form of Indian chutneys, Korean kimchi, German sauerkraut, Chinese soybean curd, or chichi de jora, a beer made from corn in Peru. These common recipes may have served as a means of preserving food initially, but they also helped to keep many ancient cultures healthy.

The reason fermented foods have such a strong impact on health is simple: They’re a stellar source of naturally occurring probiotics, the “good” bacteria that help keep your microbiome and your gut (aka your “second brain”) balanced. What’s more, probiotics aid every aspect of brain vitality by supporting better digestion and absorption of cognition-friendly nutrients in your diet. Probiotics also reduce inflammation by bolstering your immune system, and they support the ability of neurons to communicate efficiently with one another.

In a 2013 study, researchers at UCLA Geffen School of Medicine found that participants in a small test group of 36 women who regularly consumed a probiotic-infused beverage enjoyed a marked improvement in brain activity in just four weeks. By testing their responses to emotion-recognition tasks, the researchers found that the group of women who consumed probiotics, compared to the probiotic-free control group, showed lower activity in areas of the brain linked to emotion and sensation. However, this interesting decrease appeared to have some positive (and productive) ramifications for the women, including a more steady state of emotional homeostasis (serving as an antianxiety and antidepression mechanism), as well as greater connectivity in areas of the brain associated with cognition (linked to sharper thought), such as the prefrontal cortex. This change in brain activity led the researchers to conclude that the processing of both emotion and cognition was improved simply through the use of probiotics.

Probiotics abound in many fermented foods, like yogurt and tempeh, which you may already enjoy eating. The probiotics in your gut also thrive on high fibre foods, like apples, lentils, and spinach – another reason your microbiome is so content with a plant-centred diet.

And although prebiotics don’t enter the gut-health conversation as often as probiotics do, they’re another important player in keeping your digestive tract happy.

Many fermented foods (and some non-fermented vegetables and fruits, like onions, yams, and apples) contain prebiotics, which are like the “food” that probiotics need to develop, grow, and flourish. Essentially, prebiotics are probiotic magnets that set the stage for a healthy gut. If you want to rebuild and maintain your gut’s microbiome for the benefit of your brain and your body overall, both prebiotics and probiotics should be regular fixtures in your wellness plan.

Plant food sources of probiotics and prebiotics

Probiotic foods include fermented vegetables, such as sauerkraut and kimchi. They also include cultured products, like tempeh, miso, yogurt, and kefir with active cultures (for best results, use plant-based yogurt and kefir to avoid the counterproductive and brain-detrimental inflammatory effects of dairy). Prebiotic foods include onions, garlic, yams, apples, and yacón root. All high-fibre foods are helpful for gut health (and therefore brain health) in general.

Extracts supplied with permission by Sterling. Smart Plants by Julie Morris, RRP £25, is available online and in all good bookshops.

Read previous Your Health articles here...

Read articles from our latest issue here...