Summary: A four-week randomized controlled trial found that adding a single small glass of 100% fruit juice or a smoothie to the daily diet of adults with low fruit and vegetable intake can improve mental wellbeing and reduce depression scores, without detectable adverse effects on metabolic health.
Researchers tested adults who typically consumed two or fewer portions of fruit and vegetables per day. All participants received targeted educational materials and modest weekly financial support to help overcome common barriers to healthier eating. One group reached the UK’s 5-a-day target using whole fruits and vegetables only; another reached the same target by including one daily glass of 100% fruit juice or a smoothie.
Key Facts
- Low adherence to 5-a-day: Eating five portions of fruit and vegetables daily is associated with better long-term health and reduced chronic disease risk, yet fewer than 17% of UK adults and only about 10% of teenagers meet these recommendations.
- Trial design: Forty-two adults with low baseline intake were randomly assigned to three equal groups: a control group, a group increasing intake using whole fruit and vegetables, and a group increasing intake that included one daily glass of 100% fruit juice or a smoothie. All participants received £10 per week; the two intervention groups also received an educational booklet.
- Mental health outcomes: Mood was measured with validated questionnaires for anxiety and depression. The group that included juice or smoothies recorded 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 daily fiber intake by an estimated 8–10 g, demonstrating that adding juice or smoothies did not displace fiber-rich whole produce.
- No short-term metabolic harm detected: Over the four-week trial, investigators observed no adverse effects on metabolic health markers among participants consuming fruit juice or smoothies as part of the intervention.
- Practical and cost-conscious: Investigators note that fresh produce prices and cost-of-living pressures can limit access to whole produce for many households. A daily glass of 100% fruit juice or a blended smoothie can be a shelf-stable, affordable way to help people meet nutrition targets and potentially support mental wellbeing.
Source: Newcastle University
Daily 100% fruit juice or a smoothie linked to improved mental wellbeing
After four weeks, participants in both dietary intervention groups increased their fruit and vegetable intakes to meet 5-a-day guidance, but only the group that included fruit juice or smoothies showed a statistically significant reduction in depression scores. The findings were peer-reviewed and published in the British Journal of Nutrition. The trial was funded by the Fruit Juice Science Centre.
Dr Courtney Neal, who conducted the study while at Newcastle University, commented that although most people understand the health benefits of 5-a-day, many face practical barriers. The trial demonstrated that a combination of modest financial help and tailored education enabled participants to adopt meaningful dietary changes. A small daily glass of 100% fruit juice or a smoothie proved to be a simple, cost-effective option to help people reach the 5-a-day target and may offer mental wellbeing benefits.
Hitting the targets
Meeting recommended fruit and vegetable targets is linked with long-term health benefits, including reduced chronic disease risk. In this trial, all participants started with low intake (≤2 portions/day). The two intervention arms were instructed to reach 5-a-day either through whole produce alone or by combining whole produce with one daily portion of fruit juice or a smoothie. The juice-plus group registered a mean adjusted depression score of 2.93 compared with 5.45 in the control group—an adjusted difference of 2.52 points on the 27-point depression scale.
Dietary recalls completed during the study showed both intervention groups increased fiber intake by approximately 8–10 g/day, which counters the concern that including juice would displace fiber-rich foods. The study also measured metabolic biomarkers and gut symptoms and found no short-term adverse effects linked to juice or smoothie consumption.
Dr Oliver Shannon, a senior author, highlighted that financial pressures often limit access to fresh produce. He said a daily glass of fruit juice or a blended smoothie can be a practical, shelf-stable, and budget-friendly solution to help people reach 5-a-day and that the observed reduction in depression symptoms merits further investigation, particularly for people experiencing poor mental wellbeing. Previous studies have suggested some fruit juices may improve cerebral blood flow and cognitive function, which could explain mood benefits.
Study Design
This four-week parallel-group randomized controlled trial (n=42) allocated participants to one of three groups: a control group asked to maintain their usual diet; an intervention group given financial and educational support to reach 5-a-day using whole fruits and vegetables; and an intervention group given the same support but instructed to include one daily glass of 100% fruit juice or a smoothie alongside whole produce. Mood was assessed using GAD-7 for anxiety and PHQ-9 for depression. Participants completed multiple 24-hour dietary recalls during the study to estimate changes in intake.
The study found significant increases in fruit and vegetable intake for both intervention arms and a statistically significant reduction in depression symptoms in the juice-plus group compared to control. There were no significant differences in anxiety, gut symptoms, or metabolic biomarkers over the short study period.
Key Questions Answered:
A: A small glass of 100% fruit juice or a smoothie concentrates vitamins, antioxidants, and other bioactive compounds that can support brain function. Previous research indicates certain fruit compounds may enhance cerebral blood flow and cognitive performance, and this trial shows modest mood improvements when juice helps people meet recommended fruit and vegetable intake.
A: In this trial, investigators monitored metabolic markers and found no adverse effects over four weeks. When consumed as a balanced portion within a diet designed to meet nutritional targets, a small glass of 100% juice or a smoothie did not produce detectable metabolic harm in this short-term study.
A: Cost, convenience, and shelf life can make fresh produce harder to access for many households. A daily glass of 100% fruit juice or a blended smoothie is often more affordable and easier to store, making it a practical option to help people meet dietary recommendations.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full by the editorial team.
- Additional contextual details were added by staff editors.
About this diet and depression research news
Author: Helen Rae
Source: Newcastle University
Contact: Helen Rae – Newcastle University
Image: The image is credited to Neuroscience News
Original Research: Open access. “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” by Courtney Neal, Georg Lietz, Kirsten Brandt, Anthony W. Watson, and Oliver M. Shannon. British Journal of Nutrition. DOI: 10.1017/S0007114526107569
Abstract (summary): The trial tested whether including one portion per day of fruit juice or smoothies as part of UK 5-a-day guidance affects intake, mood, and health markers. Healthy adults with low baseline fruit and vegetable intake (≤2 portions/day) completed a four-week randomized trial. Both interventions—whole produce alone and whole produce plus juice/smoothies—significantly increased reported intake and were well accepted. Depression symptoms were significantly lower in the group that included juice/smoothies compared with control. There were no short-term differences in anxiety, gut symptoms, intake biomarkers, or metabolic markers. The results indicate that modest financial and educational support, plus the option to include a daily glass of 100% fruit juice or a smoothie, can increase short-term fruit and vegetable intake and may benefit mood without detectable short-term health risks.