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A daily glass of 100% fruit juice or a smoothie, when added to a healthier diet, may help support mental well-being, according to a small four-week randomised controlled trial conducted by researchers at Newcastle University in the UK. Participants who included fruit juice or a smoothie while increasing their fruit and vegetable intake reported significantly lower depression scores than those in the control group.

The findings suggest that a simple dietary change may offer potential benefits for mood, although researchers stressed that the results need to be explored further in larger studies.

Four-week trial finds lower depression scores

The study involved 42 adults who were eating two or fewer portions of fruit and vegetables each day when the trial began.

Participants were randomly divided into three groups of 14. The first group continued with their usual diet and served as the control group. The second group received support to increase their fruit and vegetable consumption to five portions a day using whole fruits and vegetables.

The third group was also encouraged to reach the five-a-day target through whole fruits and vegetables, but additionally consumed one glass of 100% fruit juice or a smoothie each day.

All participants received £10 per week, while those in the two intervention groups were also given educational material intended to help them overcome common barriers to eating more fruit and vegetables.

After four weeks, both intervention groups had increased their fruit and vegetable intake.

However, the group that included fruit juice or smoothies showed a statistically significant reduction in depression scores compared with the control group.

Depression scores fell in juice group

Researchers assessed mood using validated questionnaires, including the Patient Health Questionnaire-9 (PHQ-9) for depression and the Generalised Anxiety Disorder-7 (GAD-7) for anxiety.

The fruit juice and smoothie group recorded depression scores that were 2.52 points lower than the control group on the 27-point scale.

The adjusted mean depression score was 5.45 in the control group compared with 2.93 among participants who included fruit juice or smoothies in their dietary intervention.

Researchers described the difference as modest but statistically significant.

The findings do not establish that fruit juice directly treats depression. Instead, they indicate an association between the dietary intervention and improved depression scores that warrants further investigation.

Fibre intake also increased

Dietary recalls collected during the trial suggested that participants in both intervention groups increased their daily fibre intake by an estimated 8 to 10 grams.

This is significant because one concern about adding fruit juice to the diet is that it might replace whole fruits and vegetables and consequently reduce fibre consumption.

In this study, however, participants who consumed juice or smoothies continued adding whole fruits and vegetables to their diets.

The results therefore suggest that the inclusion of a small serving of juice or a smoothie did not prevent participants from increasing their overall intake of fibre-rich foods.

No adverse metabolic effects reported

The study also examined metabolic health markers because fruit juice naturally contains sugars.

According to the researchers, participants who consumed fruit juice or smoothies did not show adverse effects on the measured metabolic health markers over the four-week intervention.

However, the relatively short duration and small sample size mean the results should not be interpreted as evidence that unlimited fruit juice consumption is beneficial.

Nutrition advice generally distinguishes between whole fruit and fruit juice because whole fruit provides fibre in its intact form and can be more filling. The study specifically examined 100% fruit juice or smoothies as part of an overall effort to increase fruit and vegetable consumption, rather than as a replacement for a balanced diet.

Researchers call findings promising

Dr Courtney Neal, who conducted the study while at Newcastle University and is now at the University of Liverpool, said the research showed that people with low fruit and vegetable intake could make meaningful dietary changes when provided with targeted financial and educational support.

She highlighted a small glass of 100% fruit juice or a smoothie as one potentially practical way of helping people work towards the five-a-day target.

Dr Oliver Shannon, Lecturer in Nutrition and Ageing at Newcastle University and one of the study’s senior authors, also described the reduction in depression scores as promising.

He said the finding was worthy of further research, particularly among people experiencing poor mental well-being.

The researchers also referred to previous studies reporting possible improvements in brain blood flow and cognitive function following consumption of citrus juices.

What is the five-a-day recommendation?

The UK five-a-day recommendation encourages people to consume at least five portions of fruit and vegetables each day.

Eating adequate amounts of fruit and vegetables has been associated with better long-term health and a lower risk of several chronic diseases.

Despite these benefits, many people do not meet the recommended intake. The research noted that fewer than one in five UK adults and only around one in 10 teenagers meet the five-a-day target.

The Newcastle University trial therefore focused on people who had particularly low fruit and vegetable consumption.

The intervention was designed not only to encourage healthier eating but also to address practical barriers, including the cost and accessibility of fresh produce.

Study has important limitations

Although the results are encouraging, the study has several limitations.

The trial involved only 42 participants and lasted just four weeks. A study of this size cannot establish whether the observed reduction in depression scores would persist over a longer period or apply to the wider population.

The participants also started with relatively low fruit and vegetable intake, meaning the findings may not necessarily apply to people who already consume several portions a day.

In addition, the study was funded by the Fruit Juice Science Centre, an organisation associated with the fruit juice industry. This does not invalidate the findings, but it is relevant context when interpreting the results.

Most importantly, the research does not show that fruit juice is a treatment for depression. People experiencing persistent or severe symptoms of depression should seek appropriate medical or mental health support rather than relying on dietary changes alone.

A small dietary change with potential benefits

The study adds to growing research examining the connection between diet and mental well-being. Its findings suggest that helping people increase their overall fruit and vegetable intake may have benefits beyond physical health.

For people who struggle to meet recommended fruit and vegetable targets, a small serving of 100% fruit juice or a smoothie could potentially be one practical addition to an otherwise balanced diet.

However, whole fruits and vegetables should remain an important part of the diet because of their fibre and broader nutritional benefits.

The researchers say the reduction in depression scores observed among juice and smoothie consumers is promising, but larger and longer-term studies are needed to determine whether the association is consistent and whether fruit juice itself contributes to the effect.