Table 1 Self-reported measures assessed by participants

Age, sex, height, first language, family status, level of education, employment status

Weight, smoking status, presence of hypertension

Physical activity is correlated with several environmental factors, thus we use the first seven questions of the validated European questionnaire “ALPHA” [30] to assess environmental perceptions. For the same reason, we included a question about dog ownership derived from another study by Panter et al. [31].

Physical activity is correlated with assistance from family and friends, thus, four questions are included, rated on a 4-point Likert scale (completely agree - completely disagree) adopted from another study on physical activity and residential environment [32].

International Physical Activity Questionnaire (IPAQ)-Short Form [16], intentionally mostly used validated questionnaire to assess physical activity of the last seven days. The questionnaire consists of seven questions and has acceptable measurement properties [16].

Counseling process^b

counseling content

Questions about the content of consultation regarding the lifestyle factors weight reduction, change of diet, physical activity and smoking cessation. Discussion of lifestyle factors, target agreements, received information, referral to experts/counseling centers. Questions were obtained from a study on diabetes screening by Hussain et al. [33]

future medical appointments

Question, if a medical appointment was arranged and observed. This aspect was identified in an earlier focus group with PCPs in the planning phase of the trial.

Modified questionnaire to assess shared decision making for diabetes prevention opportunities including six questions. Five questions are ranked on a 6-point Likert scale (completely disagree-completely agree), and one overall question. The original questionnaire PEF-FB-9 [34] was developed and validated for clinical encounters in the primary health care setting and people with an existing medical decision.

For assessment of readiness to change lifestyle (weight reduction, regular physical activity, healthy diet, smoking cessation) we use the stage of change model developed by Prochaska et al. [35,36,37,38], allowing allocation of individuals to different stages of readiness for change (from precontemplation through contemplation, preparation, and action to maintenance)

Changes of medical condition^b

General medical condition

Self-rated overall health question with five answer alternatives “very good”, “good”, “fair”, “bad”, “very bad” suggested by World Health Organization and already used in a national representative German study (DEGS1) [39, 40]

Depression and anxiety

The Hospital Anxiety and Depression Scale (HADS) is a validated questionnaire to assess anxiety and depression. The questionnaire consists of 14 items, seven anxiety and seven depression items and showed good reliability and validity in several settings including general population [41, 42].

Changes of diabetes risk in the intervention group will be analyzed, as well as differences between the groups at follow-up. The German Diabetes Risk Score [13] is a validated non-invasive risk score to predict the five year risk of developing diabetes. It consists of eleven questions with modifiable (dietary habits, physical activity) and non-modifiable factors (e.g. age, height, family history of diabetes). Only the intervention group receives the original questionnaire at baseline. In the follow-up the questions of the risk score are included separately without any risk output in both groups.

Perceived diabetes risk^b

Memory of diabetes risk

Participants are asked, if they can remember in which risk category they were assigned by the German Diabetes Risk Score at baseline. This question reflects the perceived importance of diabetes risk and intensity of awareness. The question is adopted by a study from Godino et al. [9].

Perceived diabetes risk

Questions about the perceived risk of already having type 2 diabetes and perceived risk of developing type 2 diabetes in the next five years are included. The questions have been already used in other studies [9, 43, 44].

Different questions regarding the understandability, length, and acceptance of the German Diabetes Risk Score. Questions were adapted from other studies, aspects synthesized by Dhippayom et al. [5]