Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Clients who wish to participate enter a 2-week run-in phase during which they take 4 placebo capsules daily. After positive evaluation of this phase clients are randomised to either the active or control condition. Participants will then start the daily use of 4 supplement capsules or 4 placebo capsules, which continues for 16 weeks. At baseline and endpoint 2 questionnaires will be administered: the Intellectual Disability Quality of Life (IDQOL-16) and the Dutch Healthy Diet Food Frequency Questionnaire (DHD-FFQ). Small hair and faeces samples will be collected at baseline and 16 weeks. The data collection will take less than an hour per client and will take place at the location where the client resides. Aggression incidents will be registered by staff members using the MOAS. Also a staff member will fill in the Social Dysfunction Aggression Scale (SDAS) at baseline and endpoint, measuring observed levels of aggression and social dysfunction. The risks of participating in this study are minimal. The use of the Bonusan Multi Vital Forte Actief, or similar supplements has not been associated with any significant health risks and side effects. Potential benefits of participating in this study is an increase in quality of life through improved nutritional status, as well as a reduction of aggressive incidents. As this is a pragmatic trial in which the main objective is to determine whether the use of supplements has the potential to reduce the number of aggressive incidents among adolescents and young adults with an intellectual disability, it is imperative to include these subjects.