A Daily Glass of Fruit Juice May Modestly Lift Mood, Newcastle Trial Finds

Adding a daily glass of 100% fruit juice or a smoothie to an otherwise healthier diet may give a modest boost to mental wellbeing, according to a randomized controlled trial from Newcastle University — though the researchers and outside experts caution that the effect was small and the study was funded by the juice industry.

The trial recruited adults who reported low intakes of fruit and vegetables and gave them support to increase their consumption to meet the United Kingdom's "five-a-day" guidance. Participants were randomly assigned either to boost their intake with whole fruit and vegetables alone or to add a glass of fruit juice or a smoothie alongside them, an arrangement designed to isolate what the juice itself contributed beyond simply eating more produce.

After four weeks, both groups successfully increased how much fruit and vegetables they were consuming. But the group that added juice or smoothies reported a reduction in markers of depression compared with the control group — scoring about 2.52 points lower on a 27-point scale. The researchers described the difference as modest but statistically significant, framing it as evidence that simple, practical dietary changes can support mental health rather than as a cure for clinical depression.

The findings come with important caveats. A roughly two-and-a-half-point shift on a symptom scale is a small effect, and a four-week trial cannot establish long-term benefits or rule out the possibility that other factors — such as the encouragement and structure participants received — influenced how they felt. Researchers also note the difficulty of fully blinding people to whether they are drinking juice, which can color self-reported mood.

Nutritionists add another note of caution about the beverage itself. While 100% fruit juice supplies vitamins and plant compounds, it delivers concentrated natural sugars without the fiber of whole fruit, which is why public-health guidance typically limits it to a single small serving a day. The mood benefit, in other words, should not be read as a license to drink juice freely.

The study was peer-reviewed and published in the British Journal of Nutrition, and it was funded by the Fruit Juice Science Centre — an industry-backed body whose involvement, the authors acknowledge, is a relevant consideration in weighing the results. Even so, the work lands amid intense scientific interest in the links between diet and mood, and its authors frame the glass of juice not as a treatment but as one easy, accessible step that might help people both eat a little better and feel a little brighter.