Design and participants
The translation process of the reward-based eating drive scales RED-9 and RED-13 developed by Epel et al. [19] and Mason et al. [20] from English to German was carried out in accordance with the International Test Commission (ITC) Guidelines for Translating and Adapting Tests [26]. Items were translated from German into English by one expert in translation with university teaching credentials, and then back-translated into German by bilingual persons as well as professional translator of questionnaires. Comparison and reconciliation of the original and back-translated items was carried out by a group of experts, followed by a second round of forward and back translation. After the translation process, data collection in this cross-sectional survey was conducted from October 2021 to October 2022 among medical undergraduates at the Johannes Gutenberg-University Mainz (Germany). All participants gave written informed consent and received a data protection declaration in accordance with the Helsinki Declaration. The study was approved by the Ethical Committee of the Landesärztekammer Rheinland-Pfalz (Germany) in accordance with ethical, medical-scientific, and legal guidelines (2019–14290). The mean age of the total sample (N = 311) was 23.29 ± 5.44 years and 28% of the participants were male (72% female). A detailed description of the sociodemographic data of the total sample is given in Table 1.
Table 1
Sociodemographic description of the study population (N = 311).
Age, M ± SD | 23.29 | ± 5.44 |
Gender, N (%) | | |
Female | 222 | (71.4%) |
Male | 89 | (28.4%) |
BMI, M ± SD | 22.93 | ± 3.55 |
BMI-class, N (%) | | |
Obesity | 18 | (5.8%) |
Overweight | 45 | (14.5%) |
Normal weight | 195 | (62.7%) |
Underweight | 53 | (17%) |
Smoking, N (%) | 29 | (9.3%) |
Education, N (%) | | |
Higher school-leaving certificate | 304 | (97.7%) |
Secondary school-leaving certificate | 1 | (.3%) |
Intermediate school-leaving certificate | 2 | (.6%) |
Others | 4 | (1.3%) |
Marital status, N (%) | | |
Single | 289 | (92.9%) |
Married | 19 | (6.1%) |
Living separately | 1 | (.3%) |
Divorced | 2 | (.6%) |
Nationality, N (%) | | |
German | 262 | (84.2%) |
Austrian | 7 | (2.3%) |
Greek | 1 | (.3%) |
American | 1 | (.3%) |
Turkish | 2 | (.6%) |
Others | 38 | (12.2%) |
Table 1
Questionnaires
Reward-based Eating Drive scale (RED; Epel et al. [19] and Mason et al. [20]): The RED scale assesses self-reported reward-related eating behaviour. The RED-9 was developed by Epel et al. [19] and also exists in a 13-item version (RED-13 [20]). Both versions measure the three dimensions of lack of control, lack of satiety and preoccupation with food. The lack of control dimension measuring loss of control over food. The lack of satiety dimension deal with not feeling full despite eating a sufficient amount of food. The third dimension, preoccupation with food, about how much time is spent thinking about food. The questionnaire consists of self-developed items and original items from the Food Craving Questionnaire (FCQ [27]), the Dutch Eating Behaviour Questionnaire (DEBQ [28]), the Binge Eating Scale (BES [29]), the Three Factor Eating Questionnaire (TFEQ [30]), and the Yale Food Addiction Scale (YFAS [22]) appear in the RED. A total score is calculated as the sum of all items and each of the three dimensions.
German version of the Yale Food Addiction Scale (YFAS [31]): The YFAS [22] contains 25 items that assess pathological levels of food addiction. The symptoms are based on the 7 symptoms of substance dependence listed in the DSM-IV-TR (e.g. withdrawal, tolerance, continued use despite problems [32]). Participants rate the items in dichotomous rating schemes, but also on frequency scales (e.g. from never to four or more times a day). A summed YFAS total score was calculated according to the continuous summed score method of dichotomous items (three items are 'primer' items and are not included in the total score; e.g. [33]), as well as a method a total symptom counting method, where total score ranges from 0 (0 symptoms of food addiction) to 7 (7 symptoms of food addiction). The YFAS has been translated into German and validated by Meule et al. [31].
German version of the Dutch Eating Behaviour Questionnaire (DEBQ [34]): This 33-item scale [28] consists of three subscales. The 10-item subscale "Restraint" (DEBQ-R) assesses restraint in eating, also known as cognitive restraint. The 10-item External Eating subscale (DEBQ-E) measures the tendency to eat in response to external food stimuli, such as the sight, taste and smell of attractive food. There is also a 13-item Emotional Eating subscale (DEBQ-Em), which measures eating triggered by specific and diffuse emotions such as anger, boredom, anxiety or fear. Participants respond to items on a scale from 1 (never) to 5 (very often). Nagl et al. [34] investigated the psychometric properties of the German version of the DEBQ.
German Version of the Food Craving Questionnaire – Trait - Reduced (FCQTR [35]): One of the most commonly used instruments to assess specific food cravings is the trait version of the Food Cravings Questionnaire (FCQ-T [27]). Fifteen items with the highest item-total-correlations in the validation study of the German FCQ-T [36] were selected from the original 39 items. Items are scored from 1 to 6 (no inverted items). All items are summed to a total score.
Demographic questionnaire and body mass index: Further information on age, gender, BMI, smoking status, education, marital status, and nationality was collected using a standardized questionnaire. For a detailed specification of BMI, the participants were classified into four BMI classes: underweight (BMI < 20), normal weight (20 ≥ BMI < 25), overweight (25 ≥ BMI < 30), and obesity (BMI ≥ 30).
Statistical analysis
The software program used to analyze the data was R v3.5.0 [37], including the associated packages of Lavaan, psych, GPArotation, and ggplot2. First, mean values (M), standard deviation (SD), corrected item-rest correlations, skewness, kurtosis and Guttman’s λ were determined for the RED-13 and the RED-9. Second, CFA with 1-factor model and 3-factor model of the RED-13 and the RED-9 were performed. Goodness of fit was assessed by adjusted chi-square (χ2), comparative fit index (CFI), the root mean square error of approximation (RMSEA) and standardized root mean square residual (SRMR). We used fit criteria of Hu & Bentler [38]: CFI > 0.95, RMSEA < 0.06, SRMR < 0.08. Third, the internal consistency of the RED was tested using Cronbach’s alpha and McDonald’s omega. Higher values of omega and alpha (.70 and above) reflect greater internal consistency [39, 40]. Fourth, Pearson correlations were used to test the extent to which the RED-13 and the RED-9 correlated with total scores on other questionnaires and with BMI.