Daily glass of 100% fruit juice or a smoothie improves mental wellbeing in a randomized trial
Summary: A randomized controlled trial found that adding a single glass of 100% fruit juice or a smoothie to the daily diet helped improve mental wellbeing and reduce symptoms of depression in adults with low fruit and vegetable intake, without causing adverse metabolic effects.
Newcastle University researchers ran a four-week clinical trial assessing whether simple dietary changes could help people meet the UK’s “5-a-day” fruit and vegetable recommendation and whether including 100% fruit juice or a smoothie influences mood and health markers. Adults who typically consumed two or fewer daily portions of fruits and vegetables received targeted financial and educational support to help them reach five portions per day. One intervention group met the target using whole fruits and vegetables only; the other met the target by adding one small daily glass of 100% fruit juice or a blended smoothie in addition to whole produce.
Key Facts
- Low compliance with 5-a-day: Achieving recommended daily fruit and vegetable intake supports long-term health and lowers chronic disease risk, yet fewer than 17% of UK adults and about 10% of teenagers meet this guideline.
- Trial design: The study enrolled 42 adults with low produce intake (≤2 portions/day) and randomly assigned them to control, whole fruit-and-vegetable only, or whole produce plus one daily glass of 100% fruit juice or a smoothie. All participants received weekly financial support; intervention groups also received educational materials.
- Mental health outcomes: Mood was measured using validated questionnaires for anxiety and depression. The group that included fruit juice or smoothies showed a modest but statistically significant reduction in depression scores—2.52 points lower on a 27-point scale—compared with the control group.
- Fiber intake maintained: Dietary recalls indicated both intervention groups increased fiber intake by an estimated 8–10 grams per day, showing that including juice did not displace fiber-rich whole foods.
- No short-term metabolic harm: Despite concerns about natural sugars in juices, metabolic health markers did not worsen over the four-week period for participants who drank juice or smoothies.
- Affordable option: Investigators note that cost and access to fresh produce are common barriers. A daily glass of 100% juice or a blended smoothie can be a shelf-stable, cost-effective way to help people reach nutritional targets while supporting mental wellbeing.
Source: Newcastle University
Research highlights: Participants who added a small daily glass of 100% fruit juice or a smoothie to a diet of whole fruits and vegetables experienced improved depression scores compared to a control group, and no adverse metabolic effects were observed during the four-week trial.
After four weeks, both intervention groups substantially increased their fruit and vegetable intake. The group that included fruit juice or smoothies reported statistically lower depression scores compared with the control group, while anxiety scores and gut symptoms did not differ significantly between groups.
Dr. Courtney Neal, who completed the study while at Newcastle University and is now at the University of Liverpool, commented that many people know 5-a-day is beneficial but struggle to meet it. The trial shows that removing common barriers—through modest financial support and clear education—makes it possible for people with low baseline intake to change their diet. A small daily glass of 100% fruit juice or a blended smoothie was one practical, affordable approach that helped participants reach the 5-a-day target and offered potential mental wellbeing benefits.
Study Design
This four-week, parallel-group randomized controlled trial (42 healthy adults with low fruit and vegetable intake) compared three arms: control (usual diet), whole fruit and vegetables only (FV), and whole fruit and vegetables plus one daily glass of fruit juice or smoothie (FV+FJ). All participants received £10 per week to minimize financial barriers; the FV and FV+FJ groups also received a co-designed educational booklet. Primary and secondary outcomes included self-reported fruit and vegetable intake, biomarkers of intake and metabolism, mood (PHQ-9 for depression and GAD-7 for anxiety), gut symptoms, and acceptability.
Post-intervention, both FV and FV+FJ groups reported higher fruit and vegetable intake than the control group. Depression scores were significantly lower in the FV+FJ group versus control; adjusted mean PHQ-9 scores were lower in the juice-inclusive group (2.93) than in the control group (5.45). No differences were found between groups for metabolic biomarkers, anxiety, or gut symptoms over the short study period.
Key Questions Answered
A: A small daily glass of 100% fruit juice or a smoothie delivers concentrated micronutrients and phytonutrients that can support brain function. The trial supports the idea that simple dietary improvements can influence mood, and aligns with research suggesting certain fruit compounds improve cerebral blood flow and cognitive function.
A: This trial monitored metabolic markers and found no adverse effects over four weeks when juice or smoothies were consumed as part of a balanced approach to meet 5-a-day recommendations.
A: Cost, convenience, and shelf life can limit access to fresh produce. A daily glass of 100% fruit juice or a homemade smoothie can be an affordable, practical option to help people reach recommended intake and improve dietary quality.
Editorial Notes
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional contextual information was added by staff summarizing the research findings.
About this research
Author: Helen Rae
Source: Newcastle University
Contact: Helen Rae – Newcastle University
Image: Image credited to Neuroscience News
Original Research: Open access. Title: “Including fruit juice and smoothies within 5-a-day fruit and vegetable intake recommendations: A randomised controlled trial investigating impact on levels of intake, mood, and markers of health.” Authors: Courtney Neal, Georg Lietz, Kirsten Brandt, Anthony W. Watson, and Oliver M. Shannon. DOI: 10.1017/S0007114526107569
Abstract (condensed)
This randomized controlled trial evaluated whether including one portion per day of 100% fruit juice or smoothies within UK 5-a-day guidance influences fruit and vegetable intake, mood, and health markers. Forty-two adults with low baseline intake were randomized to control, whole fruit and vegetable advice, or whole fruit and vegetables plus juice/smoothie, with financial support and education provided to intervention groups. Both interventions increased short-term fruit and vegetable intake and were acceptable to participants. The juice-inclusive intervention produced significantly lower depression scores than control, with no adverse changes in metabolic biomarkers over the four-week period. These findings suggest affordable, practical dietary strategies that include 100% fruit juice or smoothies may help people meet nutritional targets and support mental wellbeing in the short term.