Introduction. Using WhatsApp as a methodological tool in qualitative studies has implications for data collection, content quality and information analysis. Goals. To discuss the potential of WhatsApp platform for a qualitative research on food practices in the Millennial generation in transition to adulthood life. Methods. This study was carried out in 2019, with 22 subjects belonging to the Millennial generation, from Spain and Portugal, to increase value included data for the two countries, recruited for convenience in a snowball, with qualitative design, using indirect observation of participants and as instruments a food diary with a photograph of lunch and dinner during a week, shared with the researcher by WhatsApp, and a semi-structured interview made adhoc subsequently conducted in person to know the eating habits of the sample. The interviews were recorded and transcribed, with the subjects' consent, and the analysis was done with the NVIVO software through triangulation and content analysis. Results. The results of this experience led to the emergence of three themes that appear to be central to the problematization of the use of WhatsApp as a data collection tool at the service of qualitative methodology: the commitment generated between the interviewer and the interviewee through sharing WhatsApp; the possible inequalities in the collection of information due to having or not having internet or WhatsApp; and the ethical issue associated with sharing information on social networks. Conclusions. The use of applications like WhatsApp requires the development of guidelines and an ethical code of conduct to conduct qualitative research.