Much like the intricate relationship between the gut and brain, diet and mental health are inextricably linked — and the connection between them goes both ways: a lack of good dietary choices leads to an increase in mental health issues, and mental health issues in turn lead to poor eating habits.

When people learn that I am a psychiatrist, a brain health researcher, and a nutritionist, they often ask me how they should eat to maximize the awesome power of the brain.

Based on my work with hundreds of patients, below are the best brain-boosting foods that people aren't eating enough of. Incorporating them into your diet can improve your mood, sharpen memory, and help your brain work at peak efficiency:

1. Spices

In addition to adding flavor, spices are known their antioxidant properties. In other words, they help the brain fight off harmful free radicals and therefore prevent oxidative stress, which can damage tissues.

One of my favorite spices is turmeric — a standout when it comes to reducing anxiety. Curcumin, the active ingredient in turmeric, can decrease anxiety and change the corresponding brain chemistry, protecting the hippocampus.

I also love saffron. In 2013, a meta-analysis of five previously published, randomized and controlled trials looked at the effects of saffron supplementation on symptoms of depression among participants with major depressive disorder.

In all these trials, researchers found that consuming saffron significantly reduced depression symptoms compared to the placebo controls.

2. Fermented foods

Fermented foods are made by combining milk, vegetables or other raw ingredients with microorganisms like yeast and bacteria.

Some examples include plain yogurt with active cultures, sauerkraut, kimchi and kombucha. These are all sources of live bacteria that can enhance healthy gut function and decrease anxiety.

In the brain, fermented foods may provide several advantages. A 2016 review of 45 studies indicated that fermented foods might protect the brain in animals, improving memory and slowing cognitive decline.

Probiotic-rich yogurt can be a powerful part of your diet, but keep in mind that yogurt that undergoes heat treatment does not have the same benefits. One such example is yogurt-covered raisins — these aren't going to help your anxiety, as the heat-treated yogurt has no beneficial bacteria left.

3. Dark chocolate

Dark chocolate is an excellent source of iron, which helps make up the covering that protects neurons and helps control the synthesis of the chemicals and chemical pathways involved in mood.

In 2019, a cross-sectional survey of more than 13,000 adults found that people who regularly eat dark chocolate had a 70% reduced risk of depression symptoms.

Dark chocolate also has plenty of antioxidants, as long as you stick to the dark stuff and make sure that it doesn't have too much sugar.

4. Avocados

Avocados have relatively high amounts of magnesium, which is important for proper brain function.

The first report of magnesium treatment for agitated depression was published in 1921, and it showed success in a whopping 220 out of 250 cases.

Since then, countless studies have suggested that depression is related to magnesium deficiency. Several case studies, in which patients were treated with 125 to 300 milligrams of magnesium, have demonstrated rapid recovery from major depression, often in less than a week.

I love blending avocados, chickpeas and olive oil as a tasty spread on a low-GI toast like pumpernickel, or as a dip for fresh-cut vegetables.

5. Nuts

Nuts have healthy fats and oils that our brains need to function well, along with essential vitamins and minerals — for example, selenium in Brazil nuts.

The anti-inflammatory and antioxidant effects of omega-3 fatty acids in walnuts show great promise in improving thinking and memory.

I recommend eating 1/4 cup a day (not more — it's easy to overdo it with nuts!) as a snack or added to your salad or vegetable side dish. Nuts can even be combined into a homemade granola or trail mix that contains much less sugar and salt than store-bought versions.

6. Leafy greens

When I say that leafy greens like kale make a difference in health, my patients turn up their noses at the idea. But leafy greens contain vitamin E, carotenoids and flavonoids, which are nutrients that protect against dementia and cognitive decline.

Another benefit is that they're an incredible source of folate, a natural form of vitamin B9 that is important in red blood cell formation. Where folate deficiency may underlie some neurological conditions, improving folate status has beneficial effects on our cognitive status, and is a necessary cofactor in neurotransmitter production.

Greens such as spinach, Swiss chard, and dandelion greens are also an excellent source of folate!

Dr. Uma Naidoo is a nutritional psychiatrist, brain expert, and faculty member at Harvard Medical School. She is also the Director of Nutritional & Lifestyle Psychiatry at Massachusetts General Hospital and author of the best-selling book "This Is Your Brain on Food: An Indispensable Guide to the Surprising Foods that Fight Depression, Anxiety, PTSD, OCD, ADHD, and More." Follow her on Twitter @DrUmaNaidoo.

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