WELLINGTON - An apple a day not only keeps the doctor, but also the psychiatric counselor away for young people, according to a New Zealand study.

Eating more fruit and vegetables could make young people calmer, happier and more energetic in their daily life, researchers at the University of Otago found.

A man arranges fruits at his stall at a wholesale market in Mumbai, Jan 14, 2013. [Photo/Agencies]

Psychology researcher Dr Tamlin Conner, and Dr Caroline Horwath and Bonnie White, of the Department of Human Nutrition, investigated the relationship between day-to-day emotions and food consumption.

A total of 281 people with an average age of 20 completed an Internet-based daily food diary for 21 consecutive days, said a statement from the university Thursday.

Each day, they rated how they felt using nine positive and nine negative adjectives, and answered five questions about what they had eaten that day.

Specifically, participants were asked to report the number of servings eaten of fruit and vegetables (excluding juices and dried fruit) and several categories of unhealthy foods like cookies, potato crisps and cakes.

The results showed a strong day-to-day relationship between a more positive mood and higher fruit and vegetable consumption, but not other foods.

"On days when people ate more fruits and vegetables, they reported feeling calmer, happier and more energetic than they normally did," Conner said in the statement.

The researchers also found that eating fruits and vegetables predicted improvements in positive mood the next day, suggesting that healthy foods could improve mood.

"After further analysis we demonstrated that 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 Conner.

The study was published in the British Journal of Health Psychology on Thursday.