A free fruit smoothie every day for 16 weeks left inflammation where it was. Most people said they drank about four a week

People being treated for opioid dependence tend to eat very little fruit and veg, and their blood often carries signs of long-running inflammation. So a team in western Norway tried the simplest fix they could think of: give them fruit. A randomised trial published in Nutrients on 31 October reports what that did to inflammation. In short, nothing they could measure.

The trial ran at seven opioid agonist treatment clinics in Bergen and Stavanger from April 2022 to October 2023. Everyone taking part was on methadone, buprenorphine or morphine sulphate and said they ate fewer than five portions of fruit and vegetables a day. Most ate far fewer: about 7 in 10 reported under two portions a day. Of 460 people assessed, 319 were randomised. The intervention group was handed seven 250 mL bottles of a commercial fruit smoothie each week, collected at the clinic along with their medication, and asked to drink one a day for 16 weeks. The control group carried on with usual care.

The main measure here was high-sensitivity CRP, a standard blood marker of inflammation, along with white cell counts in 311 people and three signalling proteins (IL-8, IL-1RA and MCP-1) in a subgroup of 76 who gave finger-prick blood spots. CRP rose a little in both groups over the 16 weeks, from a typical 3.5 to 4.0 mg/L with smoothies and from 3.9 to 4.6 without. Comparing the two changes gave a ratio of 0.96, with a 95% confidence interval from 0.77 to 1.21: no clear difference either way. The other four markers told the same story.

Why might a daily smoothie do nothing? The paper offers some plain reasons. Clinics handed out 88% of the planned bottles, but among people who received at least three quarters of them, the self-reported average was 3.9 drunk a week, not seven. Interviews and consumption records hinted that some bottles went to people in the control group, which the authors call intervention leakage. Neither group was blinded, many blood samples weren't taken exactly at the start and end dates, and much of the cytokine data fell below the lab's detection limit.

There's also the question of size. The trial had a 72% chance of spotting a 40% drop in CRP and a 51% chance for a 50% drop in IL-8, so a modest effect could have slipped through. And these are secondary results: the trial was built around psychological distress, reported separately in 2025.

What stands out most is how high the inflammation markers stayed in everyone, in a group where at least half drank alcohol and about a third used stimulants every week. One bottle of smoothie a day, even when it is drunk, is up against a lot. The authors' own conclusion is that future work should look at other ways of improving how people in opioid treatment eat, rather than expecting a single added food to shift inflammation on its own.