According to the first study, children who consume five or more servings of vegetables and fruits per day have the best mental health.
Research shows that students in secondary schools have a higher intake of nutrients, which is associated with better mental health.
Experts have called for good nutrition to be part of public health strategies to improve children's mental health. The data shows that young people are experiencing poor mental health.
The Guardian reported last week that record numbers of people are seeking NHS mental health services. According to a Royal College of Psychiatrists report, almost 200,000 young people have been referred for mental health services in just three months. This is nearly twice the number of pre-pandemic levels.
This is the first time that researchers have looked into the relationship between the amount of fruit and vegetables UK schoolchildren consume, their breakfast and lunch choices, as well as mental health.
Professor Ailsa Welch, University of East Anglia's Norwich Medical School Lead Researcher, stated: Although nutrition is well-studied and has many benefits, little is known about the role nutrition plays in children's emotional well-being.
We know that poor mental health is a significant issue among young people. It is also likely to have long-term detrimental consequences.
The data was taken from the Norfolk children's and young people's health and well-being survey and analysed by her team. Participants provided information about their diets and participated in mental wellbeing tests that measured happiness, relaxation, and communication.
Welch stated that nutrition was a concern for only 25% of secondary-school students and 28% of primary school children. One in ten children was not eating fruits and vegetables.
One in five secondary-school students and one in ten primary school children did not eat breakfast. More than 10% of secondary-school students didn't eat lunch.
Dr Richard Hayhoe also from UEAs Norwich Medical School said that there was a strong connection between eating a healthy diet rich in fruits and vegetables and better mental health.
The data shows that in a class with 30 secondary students, 21 of them will have eaten a traditional breakfast and at least four others will not have had anything to eat or drink before they start classes in the morning. Three students will not have lunch before they go to afternoon classes.
Hayhoe stated that children who had breakfast were more well-nourished than those who only had a snack. Secondary school children who consumed energy drinks for breakfast had lower mental wellbeing scores than those who did not consume breakfast.
Welch said: Nutrition is an important public health target to address childhood mental well-being.