AIM: To evaluate whether dietary pattern changes, antioxidant supplementation or 5-10% weight loss could improve disease activity (skin and joint) in patients with psoriatic arthritis (PsA). METHODS: A total of 97 PsA patients were enrolled in this 12-week randomized, double-blinded, placebo-controlled trial. Patients were randomized into three groups: Diet-placebo (hypocaloric diet + placebo supplementation); Diet-fish (hypocaloric diet + 3 g/day of omega-3 supplementation; and Placebo. Food intake (3-day registry, Healthy Eating Index (HEI), and the Dietary Inflammatory Index (DII)), body composition (whole-body dual-energy X-ray absorptiometry (DXA), weight and waist circumference) and disease activity (PASI, BSA, BASDAI, DAS28-ESR, DAS28-CRP and MDA) were evaluated at baseline and after the 12-week intervention. Statistical analysis used the intention-to-treat approach. The P value was considered to indicate significance when below 0.05. RESULTS: After 12 weeks, DAS28-CRP and BASDAI scores improved, especially in the Diet-placebo group (- 0.6 ± 0.9; p = 0.004 and - 1.39 ± 1.97; p = 0.001, respectively). In addition, a higher proportion of patients achieved minimal disease activity (MDA) in all groups. The Diet-fish group showed significant weight loss (- 1.79 ± 2.4; p = 0.004), as well as waist circumference (- 3.28 ± 3.5, p < 0.001) and body fat (- 1.2 ± 2.2, p = 0.006) reductions. There was no significant correlation between weight loss and disease activity improvement. Each 1-unit increase in the HEI value reduced the likelihood of achieving remission by 4%. Additionally, each 100-cal daily intake increase caused a 3.4-fold DAS28-ESR impairment. CONCLUSION: A 12-week hypocaloric intervention provided suitable control of joint disease activity in patients with PsA, regardless of weight loss. Adding omega-3 supplementation caused relevant body composition changes but not disease activity improvement. TRIAL REGISTRATION: The study was recorded on Clinicaltrials.gov (NCT03142503).