Dietary pattern changes may be one of the key factors associated with increasing asthma prevalence. Observational studies have found negative associations between fruit, vegetable and fish consumption and risk of asthma. Experimental studies have also shown that probiotics can modulate the immune system. However, each dietary component exhibits a modest effect. The objective of the present study was to investigate the joint effect of multiple beneficial dietary components on asthma. We designed a 16-week school-based double-blind placebo-controlled randomised trial. The supplement group received fruit plus vegetable concentrate, fish oil and probiotics (FVFP supplement), while the control group received placebos. A total of 192 asthmatic children aged 10–12 years were recruited from elementary schools in metropolitan Taipei. Pulmonary function, medication usage, Paediatric Asthma Quality of Life Questionnaire (PAQLQ) score and the Childhood Asthma Control Test score were evaluated at baseline, and at weeks 8 and 16. Compared with the placebo group, the supplement group showed significant improvement in pulmonary function parameters (91 v. 178 ml for forced vital capacity (FVC), 40 v. 107 ml for forced expiratory volume in 1 s (FEV1) and 1·6 v. 4·8 % for FEV1:FVC ratio; all P values < 0·01) and had a significantly reduced proportion of those using short-acting inhaled bronchodilators and inhaled corticosteroids. However, the PAQLQ score and the Childhood Asthma Control Test score were not significantly different between the two groups, possibly because the majority of the children were treated routinely. FVFP supplements reduced medication use and improved pulmonary function in asthmatic children. The present study supports an adjuvant intervention with a combination of fruit, vegetable, fish and probiotic foods.