Can food really boost our mood? The ‘SMILES’ trial

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By The Gut Health Doctor Team

Dr Megan Rossi in a lab looking through a microscope

No doubt you’ve seen endless “mood-boosting foods” lists all over the internet. And, while diet is no magic fix for our happiness, this is one concept that’s actually backed by one of my favourite scientific studies. Just be sceptical of those lists from Dr Google… always check your sources!


Let me introduce you to the ‘SMILES’ trial – a randomized controlled trial (aka a high-quality study) by some of my colleagues in Australia (led by Prof Jacka), investigating whether changing our diets could help to support our mental health – and even manage anxiety and depression.


Here’s what you need to know…


In a nutshell: Eating as many plant-based foods as you can, across all food groups, including up to 50g fibre (alongside lean protein, fish, eggs and fermented dairy in moderation) could have a significant benefit for depressive symptoms after 12 weeks


The study

56 people (aged 18+), who had all been diagnosed with moderate to severe depression and had ‘poor dietary quality’ (i.e. low intakes of fibre, lean protein, fruit and veg; high intakes of sweets, processed meats and salty snacks), were split into two groups.


They were given different interventions for 12 weeks:


1. The diet group:

  • Attended 7 nutritional counselling support sessions (around 60 minutes) with a clinical dietitian, where they received personalised dietary advice and talked about motivations, goal setting and mindful eating
  • Followed what researchers termed a ‘ModiMedDiet’ (modified Mediterranean diet), and focused on increasing diet quality with a focus on 12 key food groups: wholegrains, vegetables, fruit, legumes, unsweetened dairy foods (such as natural yoghurt), raw and unsalted nuts, fish, lean red meat, chicken, eggs and olive oil. They ate ad libitum (i.e. freely, as they liked)
  • They were asked to reduce ‘extras’ including sweets, refined cereals, fried food, fast-food, processed meats and sugary drinks


Scroll down for the full ModiMedDiet plan and try it for yourself!


2. The control group: these participants still had 7 in-person sessions on the same schedule and length of time, but these were focused on ‘befriending’ and social support (i.e. not diet-related) to make sure any difference in the diet group was not just as a result of the dietitian consultation itself. Here, they talked about neutral topics, like sport, the news or music, or played board games to keep the participants engaged and positive.


Neither group knew the full details of what the researchers were investigating to reduce the risk of bias.


The results

The diet group significantly improved the quality of their diets, reducing their intake of ‘extra’ foods (i.e. processed foods and sweets) by an average of 21 servings a week – while increasing whole grains, fruit, legumes, fish, olive oil and dairy.


And the findings were pretty amazing. Those in the diet group had a significant reduction in their symptoms of depression – as shown by the great improvement in depression scores after 12 weeks versus the control group (by 7.1 points on the MADRS, Depression Rating Scale).


What’s more, 32.3% of the diet group actually saw their depression go into remission, compared to only 8% in the control group, based on clinical questionnaires. And with every 10% increase in adherence to the ModiMedDiet, the participants in the diet group improved their depression scores by 2.2 points.

Following the publication of this study, several others have further verified and validated the mental health benefits of add more plant foods into you diet.


Full disclosure: it’s important to note that the participants who had already been on antidepressant medication before the trial continued to stay on their medication. But in my clinic I’ve seen first hand how following this way of eating can for many get them off medications, if that is their preference, with the support of their prescribing medic.


This landmark study highlights that enjoying a diet full of whole plant-based foods, extra virgin olive oil, as well as lean proteins, fish, eggs and fermented dairy, can not only be an effective but accessible treatment (alongside medication as needed) to help manage depression.


The good news is that the diet group were more likely to stick to it than the control group – suggesting it really is possible to incorporate this diverse way of eating into daily life.


Gut health benefits

The ModiMedDiet was designed to be easy to follow, sustainable, tasty and satisfying – and last but not least, super high in gut-loving fibre! On average, it provided around 50g fibre a day, which nourished their gut microbes, with large quantities of fruits (approx 411g a day) and vegetables (709g a day).


So could our gut microbes be to thank for the diet’s benefits? Research suggests absolutely yes, at least in part – thanks to the gut-brain axis (the two-way communication between the gut and the brain).


Now, I don’t want to overstate the effects of our GM, but studies do show our microbes not only work their magic via fibre but also help to transform polyphenols (plant chemicals that were abundant in this diet) into beneficial chemicals linked with better mental health.


Give it a try for yourself and see how you feel…


The SMILES trial: ModiMedDiet protocol 

(based on the Australian Dietary Guidelines and Dietary Guidelines for Adults in Greece)

(not sure what constitutes a portion? Check out the diagram in my book)


11 key food groups: increase consumption, eat as you like to your appetite:

  • Wholegrains (5–8 servings per day)
  • Vegetables (6 per day)
  • Fruit (3 per day)
  • Legumes (3–4 per week)
  • Unsweetened dairy foods (2–3 per day)
  • Raw and unsalted nuts (1 per day)
  • Fish, preferably oily fish (at least 2 per week)
  • Lean red meats (3–4 per week)
  • Chicken, skin removed (2–3 per week)
  • Eggs (up to 6 per week)
  • Extra virgin olive oil (3 tablespoons per day) – as the main source of added fat


‘Extra’ foods: reduce consumption:

  • Red or white wine (no more than 2 standard drinks per day)
  • Sweets, refined cereals, fried food, fast-food, processed meats and sugary drinks, all other alcohol e.g. spirits, beer (no more than 3 per week)
  • Alcohol: Select red wine preferably and only drink with meals
  • Dietary composition (% total energy): protein (18%), fat (40%), carbohydrates (37%), fibre/other (3%), alcohol 2%… this is just for those who love the detail but remember we eat wholefoods, not single nutrients. 


ModiMedDiet food pyramid

ModiMedDiet food pyramid. 
(Jacka et al.)



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