Forget popping pills, it may be time to inject more fruit and vegetables into your diet to be happier, according to New Zealand researchers.

A study by Otago University suggests eating more fruit and vegetables may make young people calmer, happier and more energetic in their daily life.

The research, published in the British Journal of Health Psychology on Thursday, found a strong day-to-day relationship between more positive mood and higher fruit and vegetable consumption, but not other foods.

The study asked 281 young adults to complete a daily food diary for 21 days, recording each evening how they felt using nine positive and nine negative adjectives.

They were also asked questions about what they had eaten that day, specifically the number of servings of fruit and vegetables, and several categories of unhealthy foods such as biscuits, potato crisps and cakes.

"On days when people ate more fruits and vegetables, they reported feeling calmer, happier and more energetic than they normally did," said research leader Tamlin Conner from the university's psychology department.

Analysis showed that eating fruit and vegetables predicted improvements in positive mood the next day, suggesting that healthy foods may improve mood.

"Young people would need to consume approximately seven to eight total servings of fruits and vegetables per day to notice a meaningful positive change," said Dr Conner.

She says while the research shows a promising connection between healthy foods and healthy moods, more comprehensive studies are necessary to evaluate the influence of high fruit and vegetable intake on mood and wellbeing.

NZN