Background <p>Individuals with intellectual disability (ID) experience persistent health inequalities compared to the general population. Individual health behaviors, such as dietary practices, are strongly influenced by institutional and interpersonal determinants. Nevertheless, little is known about these determinants in Swiss institutions.</p> Aim <p>To explore institutional and interpersonal determinants of dietary practices among residents with ID living in institutional accommodation in Switzerland.</p> Methods <p>A qualitative descriptive research design was chosen. Convenience sampling was used to recruit three social institutions from German-speaking Switzerland, as well as caregivers and parents of their residents. Thirteen semi-structured interviews with caregivers and parents of individuals with ID and four separate staff interviews on the institutional food environment were conducted between May and November 2022. They were transcribed verbatim and analyzed using qualitative content analysis.</p> Results <p>At the institutional level, the extent of residents’ self-determination regarding dietary practices, their involvement in food processing and cooking, institutional approaches towards body weight management and resource constraints were important dietary practices determinants. At the interpersonal level, the most important influencing factor was the opinion and knowledge of carers and parents regarding nutrition.</p> Conclusions <p>The adoption of a health promotion ethos in institutions would create health-promoting environments and encourage more balanced dietary practices among individuals with ID. Attitudes among residents and staff could be improved through nutrition and health promotion training provided to caregivers by nutrition and health specialists. Additional resources are essential for sustainable health promotion to improve the long-term health of people with ID.</p>