Newcastle Researchers Find Surprising Fruit Juice Link

A daily glass of 100% fruit juice or a smoothie was linked to improved mental well-being in a small study carried out by researchers at Newcastle University.

The Newcastle-led research examined whether helping people reach the UK's 5-a-day fruit and vegetable target could influence their diet, mood and wider health. Researchers recruited 42 healthy adults who had been eating no more than two portions of fruit and vegetables each day and followed them during a four-week randomised controlled trial. The peer-reviewed study was published online in the British Journal of Nutrition in May 2026.

Participants were split into three groups. One continued with its usual diet, another received support to reach 5-a-day using whole fruit and vegetables, while the third worked towards the same target but included a daily portion of fruit juice or a smoothie.

Daily juice was linked with lower depression scores.

At the end of the four weeks, researchers found that people in the fruit juice and smoothie group recorded lower depression scores than those in the control group.

According to the study data supplied by Newcastle University, scores were 2.52 points lower on the 27-point PHQ-9 depression scale after adjustment, with an average score of 2.93 in the juice and smoothie group compared with 5.45 among controls. Researchers described the difference as statistically significant, although the relatively small trial meant the results needed to be interpreted cautiously.

The findings did not establish that drinking fruit juice treated or prevented depression. Instead, they suggested that including a modest serving alongside a healthier diet could warrant further investigation as researchers explored links between nutrition and mental well-being.

The study also reported that participants receiving dietary support increased their fibre consumption by an estimated 8 to 10 grams a day. That was significant because it suggested adding juice or a smoothie had not prevented participants from eating more fibre-rich whole fruit and vegetables.

NHS advice still limited juice to one small glass.

The findings were particularly interesting because fruit juice had sometimes attracted criticism over its sugar content. Current NHS guidance stated that unsweetened 100% fruit juice, vegetable juice and smoothies could contribute to 5-a-day, but recommended limiting their combined consumption to 150ml per day. That was equivalent to one small glass and counted as a maximum of one daily portion, regardless of how much juice or smoothie someone drank.

The NHS also recommended consuming juice and smoothies with meals because crushing or blending fruit released sugars that could contribute to tooth decay. An adult portion of fresh, frozen or canned fruit and vegetables was generally 80g.

Those figures provided useful context for the Newcastle research. The study had not suggested replacing whole fruit and vegetables with juice. Instead, it examined whether a small daily serving could form part of a broader effort to improve fruit and vegetable intake.

Newcastle scientists called for further research.

Researchers said the mental well-being result was promising and deserved further investigation, particularly among people experiencing poorer mental health. The trial's 42-person sample and four-week duration meant larger and longer studies would be needed before stronger conclusions could be reached. The published paper itself described the work as a randomised controlled trial involving healthy people with low fruit and vegetable intake.

For Newcastle, the findings added another locally led study to the wider debate surrounding diet and mental well-being. They also raised a simple question for future research - whether an accessible change to people's everyday diets could ultimately deliver benefits beyond helping them reach their 5-a-day.

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