The Plants for Joints (PFJ) study is a randomized controlled trial (RCT) in which 64 patients with hip and/or knee osteoarthritis (OA) with metabolic syndrome were randomized 1:1 to receive the PFJ intervention in addition to usual care, or a waitlist control group which received usual care.¹ The PFJ intervention is a theoretical and practical 4-month program in which patients participated in group sessions to learn about a whole-food plant-based diet, sleep and stress management, and exercise.¹ The whole-food plant-based diet followed Dutch dietary guidelines, focusing on unprocessed foods such as whole grains, legumes, nuts, seeds and vegetables, while 150 minutes of moderate intensive exercise weekly and muscle strengthening exercises twice a week were implemented as recommended by the Dutch exercise guidelines.¹ After a 4-month RCT period, the waitlist control group received the PFJ intervention as well and participants were followed up every 6 months for 2 years.¹ The participants also received adherence-promoting webinars every other month and monthly newsletters after the intervention.¹

The primary outcome of this study was changes to the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) score based on a questionnaire indicating pain, stiffness, and physical function.¹ Additionally, changes in medication (pain, blood pressure, glucose, cholesterol), anthropometric measurements (weight, body mass index [BMI], waist circumference), and inflammation and metabolic markers at the end of the 2-year follow-up period compared to the start of the intervention were recorded.¹ Of the participants, 54 (84%) were female, with an average age of 63 years (standard deviation [SD]=6), average BMI of 33 kg/m² (SD=5.3) and average WOMAC score of 38.2 (SD=16.2) (indicative of a moderate to severe form of OA) at baseline.¹ 44 of these patients completed the 2-year follow-up and were included in the extension study analysis.¹

After the 4-month RCT period, the PFJ group showed significant improvements in the WOMAC score compared to the control group.¹ The control group received the same intervention after 4 months and was followed up for 2 years.¹ Combining the results from all participants, there was a significant improvement from baseline in the WOMAC total score (within group difference = -8.8, 95% CI: -12.6 to -5.1, p<0.0001) at the end of the extension study, as well as for individual components including pain (within group difference = -2.2, 95% CI: -3.1 to -1.4, p<0.0001), stiffness (within group difference = -0.6, 95% CI: -1.0 to -0.1, p=0.02), and physical function (within group difference = -6.3, 95% CI: -8.9 to -2.2, p<0.0001).¹ There were also significant improvements in weight loss, BMI and waist circumference (p<0.0001).¹ While significant improvements in HbA1c, fasting blood glucose, and LDL-cholesterol were seen 1 year after the intervention, these significant changes were not seen at the end of the two-year follow-up.¹ While no significant changes in pain medication, hypertension medication and glucose medication were observed, 7 out of 16 patients (44%) who were using cholesterol-lowering medication were able to reduce or stop their medication usage.¹

In conclusion, the PFJ intervention significantly improved pain, stiffness and physical function in patients with knee and/or hip OA with metabolic syndrome which were sustained through the 2-year follow-up.¹ Moreover, lasting body composition changes and a net decrease in cholesterol-lowering medication were also observed.¹ This study had a low drop-out rate (24%) after 1 year of the extension study, although this increased after 2 years (31%).¹ One limitation, however, was the lack of a control group given the nature of the methodology.¹ Nonetheless, long-term maintenance of clinically relevant effects has been demonstrated in this study, indicating that lifestyle modifications can be effective for OA patients in the long term.¹