Can The Food We Eat Really Affect Our Mental Health?

We’ve all heard the phrase, you are what you eat, but we likely associate it with our physical health.  It doesn’t help that for decades we were told that eating fat makes us fat.  But, we think it’s one of the most accurate phrases you will ever come across. 

Your body has jobs to carry out and to do those jobs it needs certain things, those things come largely from the food we eat.  But this also applies to our brain.  Over the last few years we have learned in much greater detail just how much the food we eat can affect our mood and well-being.  So, let’s take a look at how this happens and whether there are dietary changes you can make to support your mental health.  

The Gut-Brain Axis

It’s slightly easier to understand the link between the food we eat and our mental health if we consider that our mental health is influenced by what’s going on in our brain.  

We must also accept that ultimately that the food we eat influences what is going on in our gut.

What we now know is that our gut and brain are intricately linked, and this connection is known as the gut-brain axis (GBA).  

One of the main connectors is known as the vagus nerve.

This nerve extends from the brain and wanders throughout the body.

We first acknowledged its role in the gut-brain axis through vagotomy experiments.  We found that when surgically cut, certain digestive functions could be stopped in the human body. The main purpose of this was initially to reduce stomach acid secretion to prevent gastric ulcers.  However, as a side effect to this surgery, we found that this procedure could block behavioural depression.  

A population-based study of patients suffering with ulcers demonstrated that those who did not undergo vagotomy were more likely to suffer a mental health disorder compared to those who did undergo vagotomy.

Now we’re not advocating everyone severs their vagus nerve, but it does give us an indication that what is going on in our gut can influence our mood and well-being.

So, what could be going on in the gut that could affect our mood and well-being?

One of the most significant is known as gut dysbiosis.  This is when there is an imbalance between the beneficial and less than desirable bacteria in the gut.  We all possess a microbiome, which is a community of microbes that lines our digestive tract.  The microbiome provides a layer of defence, keeping less than desirable bacteria in check, and its health is dependent on several factors, including the diet we choose to eat. 

When the beneficial bacteria in our gut are thriving, they produce metabolites which influence all systems in our body, including our brain, and subsequently our mood and behaviour.  When less than desirable bacteria are thriving, things can start to go awry. 

What we now know is that certain dietary patterns can support a healthy and diverse microbiome and therefore support our mental health.

So what are these dietary patterns?


Fibre is a non-digestible carbohydrate and the beneficial bacteria in our guts thrive on fibrous diets!  When we eat fibre, it makes its way through our digestive system largely untouched until it gets to our large intestine.  This is where our bacteria get to work.  They ferment fibre and produce compounds known as short-chain-fatty-acids (SCFAs).  SCFAs are known to play a role in mental health; butyrate particularly has been seen to improve symptoms of depression.  

Increasing data has suggested a link between eating a high fibre diet and lower risk of psychological distress.

Inflammation in the Gut 

There are a number of things that can result in inflammation in the gut, and there is increasing data that suggests those with chronic low-grade inflammation may be at increased risk of major depressive disorder. Over a period of nine years, one study found that inflammatory markers were more strongly associated with sickness behaviour symptoms of depression.  

Another study found that inflammation in the gut was associated with more severe depressive and anxiety symptoms. 

Risk factors for increased inflammation in the gut include:

  • Diet high in saturated fat, 
  • High alcohol intake, 
  • Low intake of vitamin A, zinc, folate and vitamin D.
  • Low intake of omega-3 fatty acids, 
  • Insufficient intake of pre and probiotic foods. 

The Perfect Diet for Optimal Mental Health 

We are starting to build a picture of how the food we eat can influence our mental health, and many studies are now considering if there is an optimal diet to support our mood and well-being.  

The most noted would be the appropriately named SMILEs trial. 

‘SMILES’ was a 12-week trial of dietary intervention in the treatment of moderate to severe depression.  The SMILEs trial concluded that dietary intervention was effective in supporting patients with depression.  

So, what was the SMILEs diet?

Participants in this trial were encouraged to eat:

  • Whole grains (5–8 servings per day)
  • Vegetables (6 per day);
  • Fruit (3 per day),
  • Legumes/beans (3–4 per week);
  • Low-fat and unsweetened dairy foods (2–3 per day);
  • Raw and unsalted nuts (1 per day);
  • Fish (at least 2 per week);
  • Lean red meats (3–4 per week);
  • Chicken (2–3 per week);
  • Eggs (up to 6 per week); and
  • Olive oil (3 tablespoons per day).

In addition, participants were encouraged to reduce their intake of ‘extra’ foods which included:

  • sweets, 
  • refined cereals, 
  • fried food, 
  • fast-food, 
  • processed meats,
  • sugary drinks,
  • red or white wine.

There is a wealth of data to support this diet plan.  Increasingly we note that fruit and vegetable intake is beneficial for well-being.  Omega-3 intake is also correlated with improved mental health.  Furthermore, B vitamin intake is seen to support stress resilience and many of the SMILEs trial inclusions are rich in those B vitamins.  

Implementing the Perfect Diet 

It would be impossible to prescribe the perfect diet for mental health as we are all different, but we are slowly building more and more evidence as to what this looks like.  It’s clear that certain foods can support our mental well-being and other foods are less than optimal. 

The issue is implementation.  Have you tried a diet before?  How did it go?  

We can often make changes short-term, because we have a sufficient release of dopamine that keeps us on track.  But before long, the days and meals become predictable; we lose interest, and we revert to our old habits.  

Start small.  Look at what you can include in your diet rather than exclude.  Can you add an extra portion of vegetables to your meal 3 times a week?  Can you do that for a month?  Then 2 months? Can you eat a handful of nuts when you drink your mid-morning coffee?  Habit stacking is a great way to stick with new behaviours.  

The word “diet” comes from the Greek, “diaita” which means way of life.  Ultimately, optimal eating patterns need to become a way of life and hopefully, our mental health can reap the rewards.