How diet and gut microbiota affect depression and brain health

We’ve heard that ‘we are what we eat’ and a lot of us know all about being ‘hangry’ (when we’re a little unreasonable because we’re hungry, a phenomenon that instantly goes away when we eat something – like the chocolate bar ads!) but now we’re being told that our gut microbiota could be playing with our minds on a bigger scale? Great Health spoke to Professor Felice Jacka and Dr Amy Loughman about how diet and gut microbiota plays a role not just in mental health but also brain health in children, adolescents and adults.

What is gut microbiota? Is it like the little army of happy blobs on the ads on TV?

The gut microbiota is an entire community of microorganisms - bacteria, fungi and viruses that live throughout the gut, mostly in the large intestine. I guess they are a bit like a miniature version of those on TV but far more complex than an army!

Do I actually need to worry about them? What do they do?

Well, maybe not worry, but it is worth sparing a thought for these little guys. It turns out the gut microbiota plays a huge role in our health, not only in the gut but throughout the body including our metabolic health, our immune system and our brains. They’re so important that the gut microbiota has been referred to as the ‘forgotten organ’.

What’s better – taking a probiotic or improving your diet?

In general, it is much better to improve the whole diet than to reach for a pill or supplement.

It seems easier to take a pill, why is changing what I eat better?

So many reasons! In the case of probiotics, fermented foods that are high in probiotics have important features of real food, such as fibre and polyphenols, that can’t be found in a pill. And our bodies know how to absorb nutrients from food - they have lots of practice at digesting food! On the other hand, there isn’t much good evidence about whether all probiotic supplements survive the journey through stomach acid to actually get to the large intestine, which is where they are most needed. Also, most probiotic supplements only have one or two strains whereas eating the right foods can encourage many different healthy strains to grow.  

Why does this have anything to do with my mood?

The gut microbiota and the brain are constantly talking to each other. So, the health of the gut can have direct effects on the brain and our mood. For example, the gut is involved in the production of serotonin, an important brain chemical that affects our mood. And the gut microbiota of babies’ is involved in their brain development. So, it’s important to get it right even at the start of life.

What do you mean when you use the term brain health?

Brain health means having good mental health, and the absence of neurological conditions such as stroke, epilepsy and Alzheimer’s disease.

How does this all differ for teens to adults? Do I need to have a different menu for my family members?

The gut microbiota seems to go through natural changes throughout the lifespan, changing from birth and early life right through adulthood. But apart from special cases like food allergies, a good diet can be pretty well the same for the whole family. The simplest way is to follow the Australian Dietary Guidelines – plenty of fresh fruit and vegetables, legumes, nuts and seeds, wholegrains, healthy fats (olive oil and fats from nuts and avocadoes), and try to avoid processed food. Processed foods have added fats, sugars, artificial sugars and emulsifiers, and our guts don’t like any of those.

Is there anything else we should know about gut microbiota?

It’s never too late to improve your diet and change your gut microbiota. Changes to diet can affect the bacteria in as little as two days!

At a glance

  • Microbiota is the community of microorganisms that live in the gut.
  • Our gut microbiota play a critical role in our metabolism, body weight, glucose regulation, our immune function and mental and brain health
  • Unhealthy diet is now the leading cause of death across middle- and high-income countries and number two across the globe
  • Mental disorders – and depression in particular – are the leading causes of disability globally
  • The fact that unhealthy diet and mental disorders are closely linked has very large implications for public health and prevention
  • The gut and its resident microbiome may be the key pathway that links diet to mental and brain health. It’s critical to look after it!
  • Avoid processed foods, that feed the ‘bad’ bugs and hurt our gut lining!

Food that encourages good microbiota

  • High fibre foods like fresh veggies (lots of different colours and types), legumes (lentils, beans and chickpeas), fruits and wholegrains (oats, barley, rye, quinoa, wholegrain couscous, freekeh etc.)
  • Fermented foods like yoghurt, kefir, sauerkraut and sourdough bread.