This is a BIG QUESTION, but the evidence is accumulating and it looks like the answer is YES!

It can be challenging to scientifically identify a cause-and-effect relationship between the foods we eat and various disease states. That’s largely because food and lifestyle-related diseases can take decades to manifest.

Until very recently, scientists utilised epidemiological studies to search for links between diet and depression. These are observational population studies that track groups of people over several years, and even decades, to reveal the long-term impact of their food and lifestyle choices.

And to date, a consistent body of these epidemiological studies, across different countries and age groups, have shown two clear associations:

1. there is an inverse association between the Mediterranean Diet (characterised by the high intake of vegetables, fruit, whole- grains, nuts, seeds and fish, with limited processed foods) and depression; ie, the more closely the Mediterranean diet is followed, the lower the incidence of depression; and

2. there is a positive association between high intake of processed foods (high in processed, high-fat, high- sugar foods, sweets, desserts, fried food, processed meats, and refined cereals) and depression.

But epidemiological studies can’t determine rock-solid cause-and-effect relationships, only associations. So while scientists knew there was a link between diet and depression, no one could say definitively whether a poor quality diet can cause depression or whether it is simply the case that being depressed causes people to make poor quality food choices...

Until two ground-breaking Australian studies were published last year, the SMILES Trial and the HELFIMED Trial...

These were a different kind of study, one that can demonstrate cause-and-effect - a Randomised Controlled Trial (RCT).

In this case these two RCT's were specifically designed to answer the question “If a depressed person improves their diet, will their depression also improve?” 

The SMILES Trial: Supporting the Modification of lifestyle in Lowered Emotional States

The SMILES Trial was run by the Deakin University Food & Mood Centre, headed by Professor Felice Jacka, and was designed to investigate whether switching from a standard Australian diet (heavy in refined and junk foods) to a healthy Mediterranean-style whole foods diet would improve depressive symptoms in people with moderate to severe depression.

The researchers specifically recruited participants whose diet was low in fruit, veg, fibre and lean protein, and high in sweets, processed meats, and salty snacks (otherwise known as “the Standard Australian/Western Diet”) and excluded those who were already eating a healthy diet.

The SMILES trial ran for 3 months. Participants were randomised to either a “control” program of social support (with no food/diet element), or a dietary intervention where they were advised and supported in making improvements to their diet so that it would ideally resemble a modified Mediterranean diet.

They called it "the ModiMed Diet". Like the traditional Mediterranean diet, the ModiMedDiet was designed to be rich in vegetables, fruits, wholegrain cereals, oily fish, legumes, raw, unsalted nuts and seeds, and extra virgin olive oil (as the main source of added fat), as well as  reduced fat dairy.

The key modification to the Mediterranean Diet was the inclusion of a “moderate amount” of lean red meat in the diet (3 - 4 times per week). Researchers justified this modification on the basis that:

1. red meat is a rich source of iron, zinc, and vitamin B12, which studies have shown can play a potentially protective role in nutritional psychiatry,

2. 38% of Australian women aged 19–50 years have inadequate intakes of iron; and

3. epidemiological (population) studies show that women consuming less (or more) than the recommended intake of red meat were more likely to have clinical depressive and/or anxiety disorders.

So the SMILES/ModiMed Diet specifically comprised the following:

• whole grains (5-8 serves/day)

• vegetables (6 serves/day)

• fruit (3 serves/day)

• legumes (3-4 serves/week)

• low-fat, unsweetened dairy foods (2-3 serves/day)

• nuts (1 serve/day)

• fish (at least twice/week)

• chicken (2-1 times/week)

• lean red meats (3-4 times/week)

• eggs (up to 6 a week)

• olive oil (3 tablespoons/day)

Or in food pyramid format:

The diet’s macronutrient composition was:

• 39% total fat: but note that olive oil, a monounsaturated fat, was the main source of added dietary fat.

• 37% carbohydrates: recognising that not all carbs are created equal, the ModiMed Diet emphasised healthy, whole unprocessed carbs like legumes, veggies and whole, unprocessed grains. And it sought to eliminate or minimise processed, refined carbs.

• 17% protein: although the Mediterranean Diet was modified to include red meat, lean not fatty cuts were emphasised.

SMILES Diet recipients received one-on-one information and support from a dietitian, and a hamper of SMILES Diet foods to get them started, but were advised to buy their own foods, cook their own meals and consume the diet “ad libitum” (according to appetite), as the diet intervention did not have a weight loss focus.

And the results of the SMILES Trial were very encouraging!

After 3 months, the group assigned to the ModiMed/SMILES Diet had an almost 300% greater improvement than the control group - and a third of them had scores so low they no longer met the criteria for depression!

HELFIMED: Mediterranean Diet plus fish oil supplements

Like the SMILES Trial, the HELFIMED Diet was also an Randomised Controlled Trial that ran for 3 months, and measured the impact on depression of a modified Mediterranean Diet against a control of social support. 

In the HELFIMED Study, the Mediterranean Diet was modified to add in extra Omega 3 Fatty Acids; participants were assigned to take two fish oil capsules each day, with each capsule containing containing 450mg DHA and 100mg EPA.

In contrast to the SMILES trial, where participants received one-on-one nutrition advice and were responsible for their own food shopping, HELFIMED participants undertook fortnightly group cooking workshops and received fortnightly food hampers.

Both the SMILES and HELFIMED Trials scored participants according to how closely they followed their assigned diet, but the HELFIMED Trial also took blood samples to measure participants' levels of omega 3 fatty acids, and included a further follow-up of study participants after 6 months to assess whether any changes had lasted.

And as with the SMILES Trial, the HELFIMED results were were encouraging!

The HELFIMED investigators found that the magnitude of improvement of those on the modified Mediterranean Diet was almost double that of the control. The more closely participants adhered to the HELFIMED Diet, the more their depression, anxiety, negative affect and quality of life improved. And interestingly, those who ate a greater variety of vegetables saw the greatest improvement.

And while investigators didn't find a correlation between participants' omega-3 levels and depression, they did find that Increased EPA was significantly associated with reduced stress and anxiety, and increased DHA was associated with improved stress and negative emotions.

And encouragingly, HELFIMED investigators found that the benefits of the modified Mediterranean diet were sustained when they went back and checked up on participants 6 months later.

So the evidence is stacking up and it is looking promising:

Following Mediterranean Diet (modified to add in lean meat and/or omega 3 essential fatty acids) and "crowding out" highly processed junk foods, just might improve your mood if you suffer from mild-to-moderate depression.

But I do have a few observations and words of caution:

• These studies were the first of their kind and, whilst promising, are not the final word. They are simply a new and exciting piece in a larger puzzle. Further studies are needed to confirm these findings, and we can expect the scientific community to respond by running similar studies to see if they find consistent results.
  

• Neither the SMILES nor the HELFIMED Diets were "diet-diets". What I mean by that is that they were not restrictive, weight-loss diets. No one went hungry, no one counted calories and no one stepped onto a scale. So please don't equate the benefits seen in the SMILES and HELFIMED Trials with deprivation or "dieting". They were just sensible diets where the abundance of whole foods "crowded out" the ultraprocessed junk.
  

• By no means is anyone suggesting that a person suffering moderate to severe depression should ditch their antidepressants and load up on kale. If you are suffering from depression and would like to try a Mediterranean diet, if you are on medication or under treatment of any kind for depression, DO NOT just take yourself off medication. Depression is a very serious medical condition, one that can be fatal if not carefully managed. And your life is WAY TOO PRECIOUS to mess around with. So please make sure you are getting all the help you need, including antidepressants if your doctor or psychiatrist recommends them.
  

• Diet and medication are not “either/or” propositions. In fact, the SMILES Trial specifically included people who were on medication for their depression. So if you are currently taking medication for depression, it is not necessary to go off it. You can absolutely adopt a healthy Mediterranean-style diet in addition to your current treatment. Just make sure you let your doctor know you are making some changes to your diet and keep track of your mood to help you and your doctor assess whether your medication should be adjusted over time.
  

• The Mediterranean Diet is one of the most comprehensively researched diets in the world, and is associated with so many health benefits, including reduced risk of heart attack, stroke, obesity, type 2 diabetes and even some cancers. So there is very, very little downside for anyone choosing to move their diet in a more "Mediterranean" direction by crowding out the not-so-healthy stuff (sugary sodas, alcohol, processed meats, fast food, fried foods, sweets and refined carbs) with healthy nutrient-dense foods. And that includes people living with depression or anxiety. And remember, HELFIMED investigators found that those who ate a greater variety of vegetables saw the greatest improvement.
  

• It's significant that the HELFIMED Trial included regular group cooking workshops. These were included to help participants adhere to their new healthier diet, and they seem to have been very effective. So if you are keen to try a healthier Mediterranean-style diet, feel free to hit me up for one-on-one or group cooking classes!

REFERENCES:

Molendijk M, Molero P, Sánchez-Pedreño FO, Van der Does W, Martínez-González MA. Diet quality and depression risk: a systematic review and dose-response meta-analysis of prospective studies. Journal of affective disorders. 2017.

Opie RS, O’Neil A, Itsiopoulos C, Jacka FN. The impact of whole-of-diet interventions on depression and anxiety: a systematic review of randomised controlled trials. Public health nutrition. 2015;18(11):2074-93.

Sarris J, Logan AC, Akbaraly TN, Amminger GP, Balanzá-Martínez V, Freeman MP, Hibbeln J, Matsuoka Y, Mischoulon D, Mizoue T, Nanri A. Nutritional medicine as mainstream in psychiatry. The Lancet Psychiatry. 2015;2(3):271-4.

Jacka FN. Nutritional psychiatry: where to next?. EBioMedicine. 2017;17:24-9.

Marx W, Moseley G, Berk M, Jacka F. Nutritional psychiatry: the present state of the evidence. Proceedings of the Nutrition Society. 2017;76(4):427-36.

Jacka FN, O’Neil A, Opie R, Itsiopoulos C, Cotton S, Mohebbi M, Castle D, Dash S, Mihalopoulos C, Chatterton ML, Brazionis L. A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’trial). BMC medicine. 2017;15(1):23.

Opie RS, O'Neil A, Jacka FN, Pizzinga J, Itsiopoulos C. A modified Mediterranean dietary intervention for adults with major depression: Dietary protocol and feasibility data from the SMILES trial. Nutritional neuroscience. 2017;20:1-5.

Parletta N, Zarnowiecki D, Cho J, Wilson A, Bogomolova S, Villani A, Itsiopoulos C, Niyonsenga T, Blunden S, Meyer B, Segal L. A Mediterranean-style dietary intervention supplemented with fish oil improves diet quality and mental health in people with depression: A randomized controlled trial (HELFIMED). Nutritional neuroscience. 2017;8:1-4.