An apple a day may help keep the doctor away — but an ounce of nuts a day is associated with keeping depression at bay.

That's the new finding published in the journal Clinical Nutrition. Researchers found that folks who ate an ounce of nuts — such as walnuts, pistachios, and almonds — daily reduced their risk of depression by 17%.

Theories as to why nuts promote mental health range from their positive impact on the gut microbiome, which is known to have a direct influence on how brain neurotransmitters function, to their anti-inflammatory powers, which can improve physical stress levels and the function of all your bodily systems. 

Here are some of the benefits:

• The super-dose of omega-3s that walnuts deliver is especially brain-friendly — reducing inflammation, improving circulation, and slashing dementia risk. Randomized, controlled trials show it makes your brain about 6 years younger.

• Almonds deliver phenolic acids, which relieve depression.

• Pistachios help improve glucose metabolism, improving management of diabetes; elevated glucose levels are associated with an increased risk of depression. 

Then there's the fact that people who eat nuts daily may also have other healthful habits, such as consistent physical activity, good sleep routines, and life-enhancing nutrition.

But remember that nuts deliver a good dose of calories too, so don't add them to your daily intake. Make them an essential part of it.