Introduction: The dietary habits of the population are undergone dramatic changes in recent years, with an increasing proportion of people adopting different variants of plant-based diets, limiting their consumption of food of animal origin. Moreover, the shift toward a plant-based diet is supported by scientific reports promoting them as a more sustainable dietary option, which is necessary to adopt on a global scale to mitigate the human influence on climate change. However, despite their growing popularity, many questions regarding their safety and long-term health effects remain unanswered. One of the biggest concerns is the health impact during childhood and adolescence, due to the higher risk of development of severe nutritional deficiencies accompanied by the lack of good quality evidence to guide clinical recommendations and management in those groups. To close the knowledge gap, we decided to establish a family cohort study with increased representation of vegetarian and vegan families with the aim to describe not only adult and child-specific outcomes associated with plant-based diet, but also shared family risks. The aim of the presented manuscript is to introduce the background of the establishment of the family cohort study and provide a description of its protocol. Methods: To investigate the long-term effect of these newly emerging dietary habits, a cohort of families with at least one child under 7 years of age and with the same diet followed by all members was established. The goal for the first year of the study was to recruit at least 40 vegetarian, 40 vegan, and 60-80 omnivore families. At the time of enrollment, biological samples, as well as medical history, together with 3 day dietary records, were taken. The initial active follow-up is planned for at least 5 years. Ethics and dissemination: The study was approved by the Institutional Review Board no. EK-VP/391012. The results of the study will serve as a basis for future research, as well as clinical guidelines and dietary recommendations in Czechia and neighboring regions.

The authors have declared no competing interest.

The work is supported by Ministry of Health grant no. NU21-09-00362.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study is conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee of Faculty Hospital Kralovske Vinohrady (protocol code EK-VP/58/0/2019).

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

Data are not publicly available.