The link between diet and depression

22nd March 2021 | Sarah Maguire

Young people should be eating more fruit and vegetables – but especially fruit – to lower their risk of developing depression, a new Macquarie University study suggests.

The association between higher fruit and vegetable consumption and preventing certain cancers and chronic illness such as heart disease is well known, and now the evidence is growing that fruit and vegies may be just as important for good mental health.

“Depression is a real problem in Australia,” says study co-author, Associate Professor Seema Mihrshahi, a nutritional epidemiologist and public health researcher. “One in four young Australians have mental health issues – a really high proportion – so any kind of interventions to alleviate that are really important.”

Fruits and vegies may be just as important for mental health as they are for physical health.

Crunching the numbers

Mihrshahi and her colleagues at Macquarie’s Department of Health Systems and Populations reviewed the literature on the subject of fruit and vegetable consumption and depressive symptoms in people aged between 15 and 45 years.

They analysed 12 cohort studies across Europe, the UK, US, Japan, Canada and Australia that followed people over time to investigate the association between their diet and mental health. The researchers found that most studies supported the evidence that eating enough fruit is associated with decreased risk of developing depression.

Fewer studies found an influence of vegetable consumption on depressive symptoms, suggesting that there may be different effects of fruit and vegetables on mental health – although Dr Mihrshahi says it could also come down to the types of vegetables people commonly eat, and the fact that we just don’t eat enough of them.

“We kind of expected it; fruits have a really high antioxidant content and the vegetables people eat are usually potatoes and the like rather than, say, leafy greens,” she says.

“We also know that very few people eat enough vegetables – only one in 20 people are following the guidelines for vegetable consumption, whereas the figure is higher for fruit.”

Very low intakes of fruit and vegetables among young people generally was an important finding from all of the cohort studies, says Dr Mihrshahi, with intakes well below the recommended guidelines.

Two and five: despite recommendations, most Aussies are still falling short.

The danger zone for young people

Australian guidelines recommend at least two servings of fruit a day and at least five of vegetables (half a cup of cooked vegies or one cup of salad constituting one serve).

The study’s lead author, Masters researcher in public health Putu Novi Arfirsta Dharmayani, says the research showed that healthy eating plummets in the age group that’s most at risk of mental health problems: “We found that there is a huge drop in fruit and vegetable consumption between the ages of 15 and 18, which is a very vulnerable group for mental health issues,” she says. The onset of depression symptoms is usually before the age of 20, during the transition to early adulthood.

“Intake from ages 15 to 30 is low – less than 10 percent of the recommended intake.”

The authors note in the study that the exact mechanisms by which fruits and vegetables are thought to lead to lower depression risk are yet to be precisely identified. However, they say there is some evidence of an association with nutrients such as magnesium, zinc and antioxidants such as vitamin C, E and folate, found in these foods.

Teens aged 15-18 are a very vulnerable group for mental health issues. They also eat less fruit and veg.

Pathway to protection

Several studies have linked folate deficiencies in particular to depression. Folate is one of the B-group vitamins found in foods such as leafy green vegetables, legumes, beans and citrus fruits, and is important in the production of neurotransmitters such as serotonin, dopamine and epinephrine, which all play a critical role in mood regulation.

“Our study has found the possible pathway where fruit and vegetable consumption can be a protective factor against depressive symptoms,” Dharmayani says.

“Young Australians should increase their intake of fruit and vegetables. We hope these findings can help in advocating for increased consumption from a young age, in the hope that we can help to prevent development of depression symptoms.”

The researchers believe that with the evidence continuing to build, there is potential to inform public policy and add positive mental health outcomes to the already extensive list of reasons as to why people should prioritise a healthy diet.

This article was originally published on The Lighthouse from Macquarie University. You can read the original here.