General information	- Age (years) - Gender (male / female) - Marital status - Education level - Profession - Current body weight (kilogram) - Length (centimeters) - Type of bariatric surgery - Date of surgery (month + year)
Patient related factors	- Do you suffer from gastro-intestinal complaints after your meals. If so, which complaints? (e.g. nausea, abdominal pain, diarrhea) - How often do you have these complaints?
MVS related factors	- Do you take a MVS? - Which MVS do you use? - Which form of MVS do you take? - How many MVS do you take per day? - What do you think of the number of MVS you have to take per day? - When do you take the MVS? - How do you take the MVS? - Do you take the MVS separately from calcium/vitamin D? - Do you take the MVS with other medication? - How often do you take your MVS? For patients who not take the MVS daily: - Why is it not possible to take the MVS daily? - If you experienced complaints after taking MVS, which complaints are involved? - When did these complaints start? - At what time do you start to feel complaints from the MVS? - Why did you stop taking MVS? - How do you feel since you stopped or switch your MVS? For patient who never take MVS: - When did you stop taking MVS? - If you experienced complaints after taking MVS, which complaints are involved? - When did these complaints start? - At what time do you start to feel complaints from the MVS? - Why did you stop taking MVS? - How do you feel since you stopped or switch your MVS?
Psychosocial and economic factors	- Are you motivated to take the MVS daily and lifelong? - Do you find it annoying that your MVS use is necessary lifelong? - Why are you not motivated? - Do you know why it is important to take MVS lifelong? - Do you think you can reduce the risk of vitamin deficiencies by using the MVS consistently? - What disadvantages do you expect from MVS use? - What do you think about the costs of your MVS? Are these costs acceptable to you? - Would you take the MVS better if the treatment period is shorter (thus not life-long)? - Do you think that reimbursement of MVS would improve your adherence to MVS intake? - Are you satisfied about the achieved postoperative weight loss? - Do you think that MVS use has influenced this weight loss? - Do you receive emotional support for lifestyle changes after surgery? - Is your MVS intake better because of this emotional support?
Healthcare related factors	- How do you rate the received explanation from the healthcare professionals about using MVS? If not/less satisfied: why are you less or not satisfied? - How do you rate the attention paid to your MVS use during medical consultations? If not/less satisfied: why are you less or not satisfied? - How do you rate the extent to which your personal preferences are taken into account by the healthcare professionals about your MVS use? If not/less satisfied: why are you less or not satisfied? - Does the healthcare professional ask about gastro-intestinal complaints due to MVS use during medical consultations? - Which points are unclear about MVS use in your opinion?

MVS = multivitamin supplement