The study, published in the British Journal of Health Psychology, investigated the relationship between day-to-day emotions and food consumption, finding that people who eating more fruit and vegetables generally score themselves as happier, and more energetic than those who consume very little.
Led by Dr Tamlin Conner from the University of Otago, New Zealand, the research team followed almost 300 consumers, asking them to fill out daily food dairies in addition to rating how they felt. The results showed a strong day-to-day relationship between more positive mood and higher fruit and vegetable consumption. There were no associations found for other food groups, including an effect from intake of less healthy foods such biscuits or cakes.
"On days when people ate more fruits and vegetables, they reported feeling calmer, happier and more energetic than they normally did," Connor said.
"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,” she added, noting that her results also indicated that a high intake of fruit and vegetables one day is linked to improved mood the following day –and so suggesting a causative link.
A total of 281 young adults – with an average age of 20 years – completed an internet-based daily food diary for 21 consecutive days.
Each day, the participants logged and rated how they felt using nine positive and nine negative adjectives, and were asked five questions about what they had eaten that day.
Specifically, participants were asked to report the number of servings eaten of fruit (excluding fruit juice and dried fruit), vegetables (excluding juices), and several categories of unhealthy foods like biscuits/cookies, potato crisps, and cakes/muffins.
To understand which comes first – feeling positive or eating healthier foods – Conner and her team also ran additional analyses and found that eating fruits and vegetables predicted improvements in positive mood the next day, suggesting that healthy foods may improve mood.
Connor said while this research shows a promising connection between healthy foods and healthy moods, more work is needed. The authors recommend the development of randomised control trials to evaluate the influence of high fruit and vegetable intake on mood and wellbeing.