Drinking a daily glass of 100% fruit juice or a smoothie as part of the UK’s 5-a-day guidance may help support mental well-being, according to research from Newcastle University in the UK.
In a randomized controlled trial, adults who typically ate relatively little fruit and vegetables received support to increase their intake. Some participants were also asked to include one glass of fruit juice or a smoothie each day as they worked toward the 5-a-day target.
After four weeks, both groups increased the amount of fruit and vegetables they consumed. However, participants who included fruit juice or a smoothie also reported lower depression scores.
The peer-reviewed findings were published in the British Journal of Nutrition and funded by the Fruit Juice Science Centre. Researchers say the results add to evidence that relatively simple and practical dietary changes may have benefits for mental health.
Dr. Courtney Neal, who completed the study while at Newcastle University and is now at the University of Liverpool, said: “While most people know eating 5-a-day can be good for your health, many people struggle to.
“Our trial showed that when people with low fruit and vegetable intake were provided with targeted financial and educational support to address common barriers to eating 5-a-day, they were able to make meaningful changes to their diet. We found that simple, cost-effective solutions, like drinking a small glass of 100% fruit juice or a smoothie daily, could help people reach their 5-a-day, with potential benefits for mental well-being.”
Reaching the 5-a-day Goal
Eating recommended amounts of whole fruits and vegetables has been associated with a lower risk of chronic disease and better long-term health. Despite those benefits, fewer than 1 in 5 (17%) UK adults and only 1 in 10 teenagers currently meet the 5-a-day recommendation.
Everyone who took part in the 4-week trial ate two or fewer portions of fruit and vegetables per day when the study began. Participants received support designed to help them increase their intake to 5-a-day.
Some participants were instructed to meet that target using whole fruits and vegetables alone. Others increased their intake of whole fruits and vegetables while also drinking one glass of fruit juice or a smoothie each day.
Researchers evaluated changes in mood using validated questionnaires that measure symptoms of anxiety and depression. Participants who consumed fruit juice and smoothies alongside whole fruit had lower depression scores than the control group.
Their scores were 2.52 points lower on a 27-point scale, a difference the researchers described as modest but statistically significant.
Fiber Intake Also Increased
Dietary recalls completed during the study suggested that both intervention groups increased their daily fiber intake by an estimated 8-10 g.
That finding indicates that including juice did not stop participants from adding other fiber-rich fruits and vegetables to their diets.
The study included 42 participants. Despite concerns about the sugar content of fruit juice, researchers found no adverse effects on metabolic health markers after four weeks among those who consumed fruit juice or smoothies as part of the intervention.
Dr. Oliver Shannon, Lecturer in Nutrition and Ageing at Newcastle University and one of the senior authors of the study, said: “Given the ongoing cost of living pressures in the UK, the price of fresh produce is often a barrier for people trying to eat more fruit and vegetables. Our study shows that drinking a daily glass of fruit juice or a smoothie could be part of the solution and help people reach 5-a-day fruit and vegetable targets.
“The finding that fruit juice drinkers had reduced depression scores is promising and worthy of further exploration, particularly in individuals experiencing poor mental well-being. It backs up studies which report improved brain blood flow and cognitive function after people drink citrus juices. Simple dietary changes — like increasing fruit intake, including through a daily glass of juice — could play a role in supporting mental well-being.”
How the Study Was Conducted
The 4-week trial included 42 people who consumed two or fewer portions of fruit and vegetables per day at the start of the research. Participants were randomly assigned to one of three groups.
The first group included 14 people who served as controls and were asked to continue eating their usual diet.
A second group of 14 participants received support to increase their fruit and vegetable consumption to 5-a-day using whole fruits and vegetables only.
The remaining 14 participants were also encouraged to reach 5-a-day through whole fruits and vegetables, but they additionally consumed one glass of fruit juice or a smoothie each day.
All three groups received £10/week. Participants in groups 2 and 3 were also provided with educational materials intended to help them make the recommended dietary changes.
Researchers assessed participants’ mood using validated questionnaires for anxiety (GAD-7 – Generalized Anxiety Disorder 7) and depression (PHQ-9 – Patient Health Questionnaire-9).
The fruit juice and smoothie group scored statistically significantly lower for depression markers than the control group. Scores were 2.52 points lower on the 27-point scale in the fruit juice group versus the control – with an adjusted mean score of 5.45 in the control group and 2.93 among participants who included fruit juices.
Participants also completed four dietary recalls during the study describing what they had eaten during the previous 24 hours. Based on those records, both intervention groups were estimated to have increased their daily fiber intake by 8-10 g.
