TLDR? Here’s the takeaway: A healthy diet with lots of fruits and veggies can improve your symptoms of depression. An unhealthy diet full of processed foods high in sugar and saturated fats can put you at risk of depression. Read on to learn more about a new study linking diet and depression, and scroll down to find out what an antidepressant diet looks like.

You probably have a personal experience with the concept that food can change your mood. Maybe you’ve felt “hanger” or anxiety melt away while breaking a fast. Maybe you have felt elated while enjoying a particularly savory meal, or giddy and then sluggish after enjoying a big bowl of ice cream.

But it’s more difficult to tune into how your diet may be impacting your mental state and your mental health on a longer time scale. Have you ever noticed feeling anxious, apathetic, sad or depressed after a week-long junk food splurge?

“There is strong epidemiological evidence that poor diet is associated with depression.” – Francis et al., 2019

Researchers at Macquarie University in Australia in collaboration with an accredited practicing dietitian published a new paper today in PLOS One on the link between diet and depressive symptoms in young adults. The paper describes a unique randomized controlled clinical trial of healthy eating and its impact on the mental health of young adults with symptoms of depression and anxiety. 

“We hypothesised that engaging in a brief diet intervention which emphasized increasing healthy and decreasing unhealthy food intake would reduce levels of depression symptoms…” – PLOS study

Young adults in the trial who were instructed to eat a healthier diet for three weeks had fewer and less severe symptoms of depression at the end of those three weeks. Their mental health significantly improved compared to that of young adults in the trial who ate their normal diets during the study.  

At a three month follow up, the researchers found that about one in five of the young adults in the diet change group had maintained the healthy diet as well as their boosted mood. 

Ready to make a diet change? Track your fruits and veggies in the LIFE Extend app.

Diet and mental health are linked. The SMILES trial was one of the first clinical trials to show that a healthy diet could be a useful treatment for people with depression. Yet scientists have long observed that poor diet quality seems to increase risk and symptoms of depression, while eating a healthy diet rich in fruit, vegetables, fish and lean meat seems to protect against depression.

So why is this PLOS One study big news? Well, most research studies on this topic have overwhelmingly been conducted in animals (like mice) or have been observational. An observational diet study involves looking at the health outcomes of individuals or groups of people already following a particular diet or lifestyle. An observational study can’t prove that diet caused the observed health outcomes, even if it can reveal interesting relationships between these factors. 

If we observe that a large number of centenarians drink green tea, we can’t conclude that the green tea is responsible for or caused their long life. There could be confounding factors. All green-tea drinking centenarians could share a similar healthy diet. Drinking so much tea could keep them from drinking sugary sodas. Or elderly people might simply be more likely to drink tea!

That is why the findings from this new PLOS One study are so interesting. Researchers randomly assigned young adults in the study to either continue their normal diets or to eat a healthier diet for three weeks. They monitored these individuals for symptoms of depression and anxiety. They also monitored their diets and measured their intake of healthy foods. By doing these things, the researchers were able to answer this question: Do dietary changes cause changes in mental health?

It looks like they do, even if we don’t exactly know how. (Although scientists are pretty sure that the mental health benefits of a healthy diet start in our gut. Did you know that you have nerves that run directly from your stomach to your brain?!)

“This study adds to the very few randomised controlled trials examining whether changing diet can improve depression symptoms,” said Heather Francis, first author on the study. “It is the only one to date that has specifically recruited young adults.”

A total of 76 young adults ended up completing the study, half of them in normal diet or control group and half of them in the diet change group. The individuals in each group, considered collectively, had similar lifestyles and moods at the beginning of the study. They had similar dietary habits – mostly poor habits with above average intake of sugar and saturated fats. They all reported depressive symptoms such as poor appetite, inability to concentrate, feeling depressed and sad, low energy levels and sleep problems. They also reported about the same number of stressful events in their lives over the course of the study. 

While young adults in both groups started with moderate depression symptoms on average, a healthy change in diet improved symptoms among individuals in the diet change group. These individuals’ depression symptoms fell to a normal range within just three weeks! 

The PLOS One study researchers used two different scales to measure depressive symptoms in young adults – the Depression, Anxiety and Stress scale and the revised Centre for Epidemiological Studies Depression scale (CESD-R). You can take the CESD-R yourself here. The average CESD-R score for people in diet change group improved from a score above 16 to a score that isn’t clinically significant for depression. 

How exactly did young adults in the diet change group eat differently? The researchers gave them educational materials and support to help them eat more vegetables (5 servings per day) and fruit (2-3 servings per day), as well as more whole grains, lean proteins, unsweetened dairy products, fish, nuts and seeds, olive oil and healthy spices like tumeric and cinnamon. They also helped them cut sugary and processed foods from their diets, including sugar, processed meats and soft drinks.

The researchers confirmed that young adults in the diet change group did indeed eat healthier during the 3-week study period. They asked them questions before and after the study to evaluate their consumption of fruits and vegetables and their “junk food” intake. 

The researchers even used a special device to measure the amount of light that reflected off of each participant’s skin, which allowed them to measure the accumulation of plant pigments called carotenoids in the layers of their skin! Carotenoids give carrots their vibrant orange hue. They come from a diet rich in fruits and vegetables.

“Individuals in the diet change group who had a greater increase in fruit and vegetable intake, as measured by change in their skin coloration, showed the greatest improvement in depression symptoms,” Francis said.

Francis and her colleagues were actually most surprised by how well young adults in the diet change group took to the healthy diet recommendations they gave them.

“Our greatest concern was whether the students would actually comply with the diet recommendations,” Francis said. “There are several barriers to making diet changes that we thought could affect young adults in particular. These include few financial resources, time constraints and low motivation, a common symptom of depression. But we made sure that our recommendations included tips to reduce cost and preparation time for healthy meals.”

For their study, Francis and her colleagues also supplied young adults in the diet change group with a helpful food basket complete with olive oil, natural nut butter, walnuts, almonds, pepitas, sunflower seeds and spices.

Sidebar: Trying to eat healthy on a budget? 

• Shop for deals at the grocery store and buy bulk foods and whole produce.
• Fresh fruits and vegetables have lower prices and better quality when they are in season. You can find these foods at farmers’ markets or on sale towards the front of the produce section. 
• Frozen or canned fruits and vegetables are nutritious and affordable options with a long shelf life. Look for no-salt-added, no-sugar-added or low-sodium canned vegetables and fruits.
• Dried beans, eggs, peanut butter and canned tuna or chicken are very inexpensive sources of lean protein.
• Grow your own food! 

What does eating for mental health look like?

An estimated 17.3 million adults in the United States had at least one major depressive episode in 2017. During one of these episodes, a person will experience a depressed mood, exhibiting loss of interest in daily activities and problems with sleep, eating, energy, concentration or self-worth. The prevalence of depression is particularly high among younger people (18-25 years old) and women. A whopping 20% or one in five female adolescents reported at least one major depressive episode in 2017. 

Could an unhealthy “western” diet have anything to do with the prevalence of depression in the United States?

Many unhealthy dietary patterns have been associated with an increased risk of depression. But these dietary patterns usually have one thing in common – increased intake of processed, sugary foods. At the same time, many different healthy dietary patterns, from a Mediterannean diet to a vegetarian diet, seem to protect people against depression. 

This may be because most healthy dietary patterns lead people away from processed foods with added sugars, salts and fats. Processed foods have been altered in some way from their original form (canned, baked, dried, etc.) and that have often had sugars, salts and fats added to them. They include food items like cereals, bread, pre-packaged meals, sausages and deli meats, chips, etc. Highly processed foods are associated with obesity – and depression.

In the PLOS One study, Francis and her colleagues found that eating fewer processed foods had the biggest positive impact on young adults’ symptoms of depression.

Other research studies have revealed similar trends – people with better quality diets are less likely to be depressed, whereas people who eat more processed and unhealthy foods are more likely to report depression and anxiety.

Take the test – Are you eating too much sugar and saturated fat?

“I personally try to buy and eat as much ‘whole’ food as possible,” Francis said. “I try to eat food that is in a recognisable form, whether that is fresh or canned or frozen. I don’t love fish but I try to eat it at least once per week (ideally twice), and I love cookies so I can’t have them in my home.”

Vegetables, organ meats like liver, fruits, fish and seafood get high antidepressant food scores. Leafy greens, fresh herbs, lettuces, peppers and cruciferous vegetables like broccoli are particularly positively associated with brain health and protection against depression. These foods contain a number of nutrients associated with improved brain and mental health, including iron, anti-inflammatory omega-3 fatty acids, B-vitamins, zinc, magnesium, vitamin D and other plant chemicals.

But how can an unhealthy diet cause depression?

We do have some clues from observational and animal studies, and some clinical trials, about how diet impacts mental health. It most likely has a lot to do with inflammation and our gut microbes. We know, for example, that people with depression often have different types and amounts of microbes in their guts than people without depression. 

Depending on what you feed them, your gut microbes can make brain-healthy compounds or harmful, inflammatory ones. And because you have nerves and chemical messengers that send signals between your gut and your brain, these compounds can impact your brain health. 

Some special gut microbes can actually make many of the vitamins that you need, from vitamin K to folate! But these microbes need dietary fibers – like those found in bananas and whole grains such as oats – to thrive in your gut.

You might not be surprised to learn that folate deficiency is associated with depression! You can consume folate in your diet from leafy greens, but your gut microbes can also create if for you, if you feed them fiber-rich foods.

Depression can be related to various micronutrient and vitamin imbalances (like deficiencies in vitamin D) that a healthy diet may help fix. Vitamin supplements, on the other hand, have typically failed to treat depression. This could be because our gut microbes, bodies and brains ideally need a complex combination of different nutrients that no single multivitamin can provide. An apple, in addition to dietary fiber (which we now know feeds gut microbes associated with brain health!), contains dozens of other plant chemicals with inflammation-fighting, cholesterol-lowering and anti-cancer properties. 

Inflammation-fighting chemicals in your food could be particularly important to your mental health; inflammation in the brain has been associated with depression.

“Chronic exposure to increased inflammation is thought to drive changes in neurotransmitters and neurocircuits that lead to depressive symptoms and that may also interfere with or circumvent the efficacy of antidepressants.” – Felger, 2018

Depression and dietary changes can also be a vicious cycle. While a poor diet may be able to cause depression, likely in conjunction with other stressors, depression may also lead people to adopt unhealthy habits.

For example, if you are depressed, you may have less motivation to eat well and be active outside in the sun. What do these two healthy behaviors have in common? They help you get enough vitamin D, which is important for your bone and brain health!

Can I eat myself out of depression?

There are many things that put you at risk of depression: stressful life events, trauma and abuse, medical problems, your genes. Diet is just one factor. It may not be a factor for everyone. We also don’t really know if it only worsens existing depressive symptoms (or improves them, in the case of a healthy diet) or if it can initiate depression in the first place. 

Many causes of depression are serious and require professional help. You shouldn’t worry about making a diet change if you are in an unsafe situation; getting help and/or removing yourself from that situation should be your top priority. You should also focus on getting help for health issues, financial and medical problems, drug addictions and other serious stressors in your life before you attempt a dietary overhaul. 

But it can’t hurt to try to cut down on sugary drinks and processed foods that could be worsening your depressive symptoms. 

If you are feeling blue for no obvious reason, especially if you know that your diet isn’t great, eating healthier is a safe bet to improving your depressive symptoms and your mood. Focus on eating foods that you can recognize, in the form that they came out of the ground (or the animal) in! 

Just remember: Less sugar, more natural colors. 

We are here for you!

 

Citation: Francis HM, Stevenson RJ, Chambers JR, Gupta D, Newey B, Lim CK (2019) A brief diet intervention can reduce symptoms of depression in young adults – A randomised controlled trial. PLoS ONE 14(10): e0222768. https://doi.org/10.1371/journal.pone.0222768