To evaluate the effects of synbiotic supplementation on insulin resistance and lipid profile in individuals with the metabolic syndrome, we conducted a randomised, double-blind, placebo-controlled pilot study on thirty-eight subjects with the metabolic syndrome; they were supplemented with either synbiotic capsules containing 200 million of seven strains of friendly bacteria plus fructo-oligosaccharide or placebo capsules twice a day for 28 weeks. Both the synbiotic (G1) and the placebo (G2) groups were advised to follow an energy-balanced diet and physical activity recommendations. Parameters related to the metabolic syndrome and insulin resistance were measured every 7 weeks during the course of the study. After 28 weeks of treatment, the levels of fasting blood sugar and insulin resistance improved significantly in the G1 group (P< 0·001). Both the G1 and G2 groups exhibited significant reductions in TAG levels ( − 71·22 v. − 10·47 mg/dl ( − 0·80 v. − 0·12 mmol/l) respectively; P< 0·001) and total cholesterol levels ( − 21·93 v. − 14·2 mg/dl ( − 0·57 v. − 0·37 mmol/l) respectively; P= 0·01), as well as increases in HDL levels (+7·7 v. +0·05 mg/dl (+0·20 v. +>0·01 mmol/l) respectively; P< 0·001). The mean differences observed were greater in the G1 group. No significant changes were observed in LDL levels, waist circumference, BMI, metabolic equivalent of task and energy intake between the groups. The present results indicate that synbiotic supplementation increases the efficacy of diet therapy in the management of the metabolic syndrome and insulin resistance.