Purpose - The purpose of this paper is to assess the impact of a worksite nutritional intervention on the dietary quality of adult workers from the city of Sao Paulo, Brazil. Design/methodology/approach - A 6-month controlled community trial was performed involving 236 workers from Sao Paulo, Brazil. The intervention was implemented through interactive software that sends recommendations about diet and physical activity by e-mail. Data were collected for all participants using a 24-hour dietary recall and also for a sub-sample containing 25.4 per cent of the participants. Diet quality was assessed by the diet quality index adjusted (DQIa) comprising 10 components (grains and tubers; vegetables; fruits; milk and dairy products; meat and eggs; beans and legumes; total fat; saturated fat; sodium; and variety), scored from 0 (inadequate consumption) to 10 (recommended consumption). Intragroup impact of the intervention was assessed according to variation in total DQIa, its components and energy consumption. Impact adjusted between groups was also determined. Findings - The intervention yielded improvements in DQIa and for the components cereals and tubers, vegetables, milk and dairy products and total fat. The workers who had a worst diet quality before the study were more susceptible to the intervention, which improved significantly the diet quality, with an adjusted impact of +6.4 points. Originality/value - Few behavioral interventions have been performed using technologies, like e-mail, to encourage a healthy lifestyle. This study shows the importance of the counseling to promote a higher-quality diet, which can result in control of the obesity.