Eating even one extra serve of fruit a day could help reduce anxiety and depression in teenagers, new research has found.
The study by the University of Sydney surveyed young people for three years, with researchers finding that eating one extra serve of any type of fruit each day was associated with a 13 per cent lower risk of depression symptoms.
It was also linked with a seven per cent lower risk of anxiety symptoms.
Meanwhile, researchers found a link between the higher consumption of sugary drinks - like soft drinks, cordials and sport drinks - with a higher risk of depression and anxiety.
The link was stronger in male teenagers, particularly for anxiety.
The study's lead author, Lily Davidson, said it showed that food choices had impacts beyond physical health.
''We're not saying eating an apple will prevent depression, or that having a soft drink will cause anxiety - mental health is far more complex than that,'' the researcher from Sydney University's Matilda Centre for Research in Mental Health and Substance Use said.
''But what you eat is one part of a young person's life that can potentially be changed, which makes these findings important from a prevention angle.''
The study was different from previous research as it excluded adolescents who already met the criteria for depression or anxiety, she said.
''One of the big questions in our field is whether poor nutrition comes before mental health problems, or whether young people experiencing poor mental health simply eat differently,'' Dr Davidson said.
''By starting with adolescents who weren't already experiencing elevated symptoms and following them through high school, we could look at whether their dietary intake was associated with the later emergence of those symptoms.''
The study followed 6537 adolescents from 71 secondary schools across NSW, Queensland and Western Australia from Year 7 to Year 10.
They were 12.5 years old on average at the start of the study, with participants doing annual surveys over four years during high school.
Senior study author Associate Professor Katrina Champion said the findings would help with prevention of mental illness in young people, rather than just treating it once symptoms develop.
An important part was making healthy food more accessible and affordable for families.
''Schools, families and governments all have a role to play in supporting healthy behaviours and better mental health for young people,'' she said.
Lifeline 13 11 14
Kids Helpline 1800 55 1800 (for people aged 5 to 25)