How does food affect our risk of depression?

Human brains need antioxidants from foods such as vegetables, fruit, legumes, wholegrains, nuts and seeds to help protect against oxidative stress a kind of rusting of the cells that's linked to depression, says Professor Felice Jacka, director of the Food and Mood Centre.

"Studies often single out the Mediterranean Diet as protective against depression but it's not the only traditional diet with this effect. In Japan, eating more foods like leafy greens, mushrooms, radish, fish, fruit, tofu and fermented food is linked to less depression, while in Norway the link is to traditional diets of fish, potatoes, fruit, vegetables, yoghurt, meat, legumes and eggs. It's a consistent pattern in countries as diverse as China, Greece, Italy and Brazil - the individual foods might vary, but diets higher in plants and healthy oils from fish and plants are linked to less depression," says Jacka, the author of Brainchanger: the Good Mental Health Diet, which looks at the links between food and human brains and how to apply the knowledge in our own kitchens.

There's also "brain manure" Jacka's name for BDNF (brain derived neurotrophic factor), a protein that acts like fertiliser, helping to maintain existing brain cells and grow new ones.

"It's relevant to mental health because people with depression often have a smaller hippocampus, the part of the brain that's key to learning, memory and mental health," she says. "Research is discovering that there are things we can do ourselves to help boost production of BDNF. Building more muscle with exercise is one and a healthier diet is another."

In animal studies some foods and nutrients such as omega-3 fatty acids, flavonoids (found in fruit, vegetables and tea), and resveratrol, a polyphenol found in red grapes, other fruits and red wine, stimulate the growth of new brain cells too. They also reduce the low level inflammation that's linked to depression, dementia and other chronic diseases, she adds.

Eating foods that feed friendly gut bacteria may also benefit the brain. Most research has been in animals, but recent New Zealand research found that giving women a probiotic supplement in pregnancy and for a few weeks after birth reduced levels of depression and anxiety, she says.

There's still much to learn about this gut-brain link, she stresses, but it's why her own diet includes fermented foods such as sauerkraut and kefir.

"They contain many of the valuable products of fermentation, including neurotransmitters and anti-inflammatory molecules which may turn out to have benefits for the brain and mental health," she says.

Jacka's 2015 study of older adults found that the hippocampus is smaller in people with diets high in sweet drinks, salty snacks and processed meats compared with those eating more nutrient-rich foods.

Too much ultra-processed food can disrupt the brain in different ways, she says. One is by edging out nutrient-rich foods that help protect the brain. The other is by stoking low-level inflammation.

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"Whole foods are generally anti-inflammatory which may help explain why traditional diets with more whole foods are consistently linked to less depression."

It's a message we need to hear at any age because food quality can influence brain health across the lifespan.

"But it's especially important for the next generation, given that around 40 per cent of Australian adolescents' kilojoules come from junk food," she says.

"Half of all mental disorders emerge before the age of 14. No one's saying that eating your veggies will prevent mental illness; it's a complex problem with many risk factors like poverty, genes, trauma and stress. But diet is one thing we can all do something about. "

Deakin University's Food and Mood Centre is offering a free three-week online course to help us all eat better. Food and Mood: Improving Mental Health through Diet and Nutrition explores how our daily diet can influence mental and brain health.

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