Abstract There is a growing recognition that social support can potentially exert consistent or opposing effects in influencing health behaviours. The present paper presents a cross-sectional study, including 2,064 adults from Italy, Spain and Greece, who were participants in a multi-centre randomised controlled trial (C4H study), aiming to examine whether social support is correlated with adherence to a healthy Mediterranean diet and physical activity. Social support data were available for 1,572 participants. The majority of the sample reported emotional support availability (84·5 %), financial support availability (72·6 %) and having one or more close friends (78·2 %). Mediterranean diet adherence was significantly associated with emotional support (P = 0·009) and social network support (P = 0·021). No statistically significant associations were found between participant physical activity and the social support aspects studied. In conclusion, emotional and social network support may be associated with increased adherence to the Mediterranean diet. However, further research is needed to evaluate the role of social support in adherence to healthy Mediterranean diet.