Feeling blue—or maybe just a little blah? Your diet could be partly to blame. Research shows getting the right nutrients over time can improve your mood, tame stress, ease anxiety and even help fight depression. Now that's something to smile about.

Talk about food for thought. Growing research shows that simply making changes in what you eat can significantly boost mood and improve symptoms of anxiety and depression.

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In a recent clinical study known as the SMILES trial, researchers split nearly 70 people-all diagnosed with depression, and all on poor diets-into two groups. The first group had no form of therapy but switched to a healthy, Mediterranean-style diet rich in fruits, vegetables, olive oil, low-fat dairy, fish, eggs, seeds and nuts. The second group met regularly with a support group and continued to chow down on sweets, processed deli meats and salty snacks.

After three months, the healthy eaters showed fewer symptoms of depression than the second group. In fact, more than a third of them no longer even met the criteria for being depressed.

Want to see what the right foods can do for your mood and mental health? The seven foods below have all been shown to help ease stress, improve mood, relieve anxiety or help fight depression. See what a difference they can make for you.

1. Chocolate

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Pictured Recipe: Mug Brownie

Finally, science backs up what many of us already know: chocolate does make you happy. In a study done at the Nestlé Research Center in Switzerland, researchers found that eating a little dark chocolate (1.4 ounces of it, to be exact) every day for two weeks reduced the levels of cortisol and other stress hormones in people who were highly stressed. Experts say it could be thanks to the antioxidants found in dark chocolate. So go ahead! Indulge. Just be sure to account for the 200-plus calories in that tasty chunk of chocolate-or you may soon start stressing over extra pounds.

2. Salmon

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Picture Recipe: Roasted Salmon with Smoky Chickpeas & Greens

Good news for worrywarts: Regularly eating salmon-and mackerel, tuna, herring and other fatty fish-can help lower anxiety, research shows. Experts say it's because of their omega-3 fatty acids, a key mood-boosting nutrient and one our bodies don't produce. Omega-3s alter brain chemicals linked with mood-specifically dopamine and serotonin. In one randomized, controlled study, medical students who took omega-3 supplements before an exam reduced their anxiety symptoms by as much as 20 percent.

3. Green Tea

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Pictured Recipe: Matcha Green Tea Latte

On a bad day, sipping a cup of tea can be just the thing to soothe your senses, calm your nerves and brighten a dark mood. Make that green tea and you may reap even more benefits, researchers say. According to a Japanese study published in the American Journal of Clinical Nutrition, drinking two to three cups of green tea a day was linked to reduced depression symptoms in elderly people. That may be due to a number of mood-boosting nutrients, including L-theanine, an amino acid that helps fight anxiety. Green tea also has some caffeine-enough for a pick-me-up when you're feeling down, but not enough to give you the jitters.

4. Oysters

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Pictured Recipe: Spicy Barbecued Oysters

Sure, oysters have a reputation as an aphrodisiac. But their mood-boosting benefits go well beyond the bedroom. Oysters are high in zinc, a nutrient that helps ease anxiety. Zinc also helps improve sleep quality, essential for staying on an even keel. Bonus: Once you get the hang of it, eating oysters can be fun-and an instant mood-lifter in itself.

Not into seafood? Get your zinc fix with cashews, eggs, liver or beef.

5. Blueberries

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Pictured Recipe: Purple Fruit Salad

With more antioxidants than any other common fruit or vegetable, blueberries deliver a bushel of brain-boosting benefits. Thanks mostly to a type of antioxidant called flavonoids, blueberries help regulate mood, improve memory and protect the brain from aging. And some experts say they may do even more. One recent animal study suggests the anti-inflammatory chemicals in blueberries may be helpful in treating PTSD and other serious mental health problems.

6. Spinach & Other Leafy Greens

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Pictured Recipe: Spring Vegetable Lasagna

Nearly half of all Americans don't get enough magnesium, a mineral that, among other things, helps reduce anxiety. Dark leafy greens like spinach and Swiss chard are loaded with it-so eating them is an easy way to get your daily vegetables and boost your brain health, too. More good sources: beans and lentils, almonds and avocados.

Related: 5 Reasons to Love Dark Leafy Greens

7. Yogurt & Other Probiotics

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Pictured Recipe: Rainbow Yogurt Bowl

There's lots of buzz these days about probiotics-fermented foods like yogurt, kimchi and sauerkraut that help keep your gut bacteria in check. Recent studies in both animals and humans suggest links between balanced gut bacteria and better mood, less stress and anxiety, and lower risk of depression.

Still, some experts caution that it's too soon to tell for sure. A recent review of 10 small but solid studies found that eating probiotics for depression and anxiety seemed to help some folks, but not others. The bottom line? Slurping a refreshing yogurt smoothie now and then won't hurt your moods-and it may help.

Watch: Foods That Help Make You Happy