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There are many reasons why people change their diet: Lose weight, lower blood pressure, ease digestive upset and improve athletic performance are a few of them.

Eating better can also improve your mental well-being, something that’s not commonly recognized. Mounting evidence suggests that’s particularly true if you have depression.

Research has linked a healthy diet pattern – e.g., a high intake of fruits, vegetables, whole grains, fish – to a lower risk of depression in adults, children and adolescents. (It’s also been associated with lower rates of anxiety and bipolar disorder.)

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A 2018 review of 11 studies involving 101,950 participants, published in the journal Clinical Nutrition, concluded that participants who ate a pro-inflammatory diet had a 40-per-cent greater risk of being diagnosed with depression or having depressive symptoms compared with those on an anti-inflammatory diet. A diet that’s heavy in red and processed meats, refined grains, added sugars and unhealthy fats can promote inflammation in the body.

Many studies have associated depression with chronic low-grade inflammation. It’s thought that inflammatory immune compounds can communicate with the brain, affecting mood, behaviour and energy levels.

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Anti-inflammatory diet for depression

While these findings don’t prove cause and effect, they do imply that eating an anti-inflammatory diet, one that’s plentiful in fruit and vegetables, whole grains, nuts and oily fish, may help guard against depression and, perhaps, help in the treatment of depression.

Recent findings from randomized controlled trials, the gold standard of scientific evidence, suggest that this is the case.

The SMILES trial, published in 2017, was the first to test whether dietary change was effective in treating depression. (SMILES stands for Supporting the Modification of Lifestyle in Lowered Emotional States.)

For the three-month study, researchers from Melbourne, Australia, assigned 67 participants with major depression to a diet group or a social support control group. Most (55) were already on some type of therapy, medication or psychotherapy.

At 12 weeks, those who were coached by dietitians to follow a Mediterranean-style diet had significant improvements in depressive and anxiety symptoms compared with participants who received only social support.

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The HELFIMED randomized controlled trial, also published in 2017, investigated whether a Mediterranean diet supplemented with fish oil could improve mental health in adults with self-reported or family-doctor-diagnosed depression. (HELFIMED stands for Healthy Eating for Life with a Mediterranean-style diet.)

Participants in the diet and fish oil group had a significantly greater reduction in depression and improved mental health after three months compared with those who attended social-support groups.

Nutrition and the brain

It’s thought that diet affects many biological pathways that underpin depression, as well as other mental-health disorders.

Whole foods such as vegetables, fruits, whole grains, fish, beans, nuts and olive oil, plentiful in a Mediterranean-style diet, contain anti-inflammatory nutrients and phytochemicals that help dampen inflammation in the body.

Antioxidants such as vitamins C and E, beta-carotene and many natural plant compounds reduce free radical damage, or oxidative stress, that may influence mental health. Higher levels of oxidative stress in the body have been associated with depression.

Sweet bell peppers, cauliflower, broccoli, tomatoes, citrus, kiwifruit, strawberries and cantaloupe are good sources of vitamin C. For beta-carotene, include dark green and orange vegetables in your daily diet such as spinach, kale, collards, carrots, butternut squash and sweet potato.

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Sunflower seeds, almonds, almond butter, hazelnuts, peanuts, peanut butter, cooked spinach, dandelion greens and wheat germ deliver plenty of vitamin E.

The B vitamin folate, found in lentils, black beans, kidney beans, cooked spinach, asparagus, artichokes, beets and broccoli, is needed for the production of serotonin, a neurotransmitter (brain chemical) that regulates mood.

Omega-3 fatty acids reduce inflammation, maintain healthy brain cell membranes, influence communication between brains cells and affect levels of neurotransmitters.

Foods that feed our “good” gut bacteria, called prebiotics, help maintain a diverse community of microbes in our gut, collectively known as the gut microbiome. That’s important since our gut bacteria produces the majority of the brain’s serotonin, a neurotransmitter that regulates mood.

Prebiotic foods include barley, oats, wheat bran, Jerusalem artichokes, asparagus, bananas, garlic, onion, chicory root and kefir.

Maintaining a healthy gut microbiome can also help reduce chronic inflammation in the body.

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Feed your brain

Your brain needs a wide range of nutrients to maintain healthy structure and function, nutrients that work synergistically to promote brain health.

Improving your whole diet, rather than focusing on one food or a single nutrient, matters most when it comes to benefitting mental health. Eat a variety of nutrient-rich whole foods and, at the same time, minimize your intake of foods that may harm the brain such as highly-processed foods, sugary foods and fatty fried foods.

Doing so can also help guard against cardiovascular disease, Type 2 diabetes, certain cancers and Alzheimer’s disease.

Leslie Beck, a Toronto-based private practice dietitian, is Director of Food and Nutrition at Medcan.

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