Introduction

The fourth and fifth editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV, DSM-5) have both defined addiction using clear diagnostic criteria [1, 2]. However, food addiction (FA) has not been formally recognized despite increasing interest and empirical evidence in the condition. Animal models have demonstrated that it is possible to develop addictive-like behaviors relating to specific foods, especially those high in sugar and fat [3]. Neuroimaging studies on human beings have demonstrated similar findings to those found in animal studies. The neuronal circuits activated by drugs in addiction are similar to the neuronal circuits activated by hyper-palatable food among obese individuals, and both circuits are modulated by dopamine [4, 5]. Therefore, an in-depth understanding of FA is needed for healthcare providers to assist such a population in overcoming this specific type of addiction and its impacts on related disorders (e.g., binge eating) or psychological impairment (e.g., depression).

Several studies have examined the prevalence of FA in different populations using the criteria for substance dependence in the DSM-IV [e.g., 6–8, 11]. Moreover, Gearhardt et al. [9] developed the Yale Food Addiction Scale (YFAS) for assessing FA based on the diagnostic criteria for substance dependence in the DSM-IV. More recently, a child/adolescent version of the YFAS (YFAS-C) was developed and validated [10]. With the development of YFAS and YFAS-C, studies concerning FA can be further empirically investigated.

However, the FA studies on children or adolescents, especially in the large Persian-speaking populations (~ 110 million people are native Persian speakers across Iran, Pakistan, Tajikistan, and Afghanistan) [12], are lacking. A major reason for the dearth of FA studies among Persian-speaking children and adolescents is the lack of a validated instrument for usage. Although one recent Iranian study translated the YFAS-C and applied the Persian YFAS-C to 222 elementary school students to assess FA [11], the study did not provide any psychometric evidence for the robustness translated YFAS-C. Researchers and healthcare providers may, therefore, hesitate to use the Persian YFAS-C because the psychometric properties are not known. Consequently, there is an urgent need to validate the Persian YFAS-C and present its psychometric properties using rigorous testing methods.

Two testing theories (classical test theory [CTT] and modern test theory) with different features in assessing the psychometric properties are warranted in examining the Persian YFAS-C. To the best of the present authors’ knowledge, most studies examining the validity of YFAS-C (and YFAS) have only used CTT and no studies have ever utilized modern test theory [8,9,10, 13, 14]. Modern test theory, such as the item response theory (IRT) model, uses the probability to convert the responses in a psychometric scale into an additive score (i.e., logit) as well as providing the psychometric properties of an instrument in a sample-free pattern [15, 16]. Consequently, the psychometric evidence derived from using IRT is not heavily influenced by sample characteristics, while psychometric evidence derived from CTT is [15, 16]. Therefore, using both theories to examine the psychometric properties of the Persian YFAS-C may integrate the current validity evidence from traditional validity methods in an understudied field [17]. More specifically, the CTT findings in the present study can help corroborate previous evidence testing the psychometric properties of YFAS-C, and findings utilizing modern test theory can provide an enhanced perspective concerning the YFAS-C’s psychometric properties.

The aims of the present study included the following: (i) to translate the YFAS-C into Persian and provide robust validity testing (including CTT and IRT models) of the Persian YFAS-C using a community sample of adolescents who were overweight/obese (OW/OB) in high schools [10]; (ii) to examine the prevalence of FA among the studied adolescents; and (iii) to examine the how Persian YFAS-C score was associated with eating symptomatology (using the Eating Disorder Examination Questionnaire, Clinical Impairment Assessment, Binge Eating Scale, and Eating Attitudes Test) and general psychopathology (using the Depression, Anxiety, Stress Scale).

Methods

Translation procedure

The YFAS-C was recently translated into Persian without any validity testing [11]. Therefore, the present study carried out an independent translation of the YFAS-C to ensure robust linguistic equivalency. More specifically, the original YFAS-C was translated according to standardized international guidelines [18, 19] incorporating the following steps. First, the YFAS-C was translated from English to Persian by two bilingual translators who were native Persian speakers. The two translators conducted the translations independently and then synthesized the two translated versions into an interim Persian version. Second, the interim Persian version was translated back into English by two native English speakers who were fluent in both English and Persian. Both back translators conducted the translations independently and had no knowledge of the original English YFAS-C prior to translation. Third, an expert panel including a psychiatrist, nurses, nutritionist, psychologist, and a psychometrician investigated the aspects of cross-cultural equivalency for all the translated YFAS-C items and the original YFAS-C items. Following this, a pre-final version of the Persian YFAS-C was generated and piloted among 36 participants to ensure its readability.

Participants and process

Between September 2018 and April 2019, a total of 1660 OW/OB adolescents were approached by trained research staff from 20 high schools in Qazvin, Iran. A total of 1189 agreed to participate (response rate of 71.6%). The inclusion criteria were that participants had to (i) be aged between 13 and 18 years (i.e., the definition from Medical Subject Headings that an adolescent is aged between 13 and 18 years [https://www.ncbi.nlm.nih.gov/mesh/68000293]), (ii) have a diagnosis of OW/OB (i.e., body mass index [BMI] ≥ 85th percentile for age and gender) according to the anthropometric parameters (i.e., weight, height, and BMI), and (iii) have parental consent to participate. The exclusion criteria were (i) being pregnant and (ii) having a cognitive impairment. Written informed parental consent and student consent was provided by all participants. The study was approved by the ethics committee of the Qazvin University of Medical Sciences (IR.QUMS.REC.1398.320).

Measures

Yale Food Addiction Scale for Children (YFAS-C)

The YFAS-C comprises 25 items that assess food addiction among the pediatric population and was modified from the adult version (i.e., Yale Food Addiction Scale; YFAS; [9]). The YFAS-C items correspond to seven criteria based on those for substance-used disorders in the fourth (text revised) edition Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR; [1]). Three YFAS-C items (Items 19, 20, and 24) are not used for testing the seven criteria but are primers for other questions [10] (see Table 2 regarding the seven criteria items). Items 1 to 18 are rated on a 5-point Likert scale (0 = never; 4 = always) and Items 19 to 25 are rated on a dichotomous (0 = no; 1 = yes) scale. All the items rated on the 5-point scale can be converted into a dichotomous scale, where 0 = no and 1 = yes, according to specific scoring thresholds for each item [20]. A criterion (given up activities; persistent desire; activity to obtain, use, recover; tolerance; inability to cut down; withdrawal; or large amount of time spent) is met if at least one item of each criterion is scored as one. Consequently, two scoring versions can be generated: a symptom count scoring version (ranging between 0 and 7) and a diagnostic scoring version (having three or more criteria met in addition to having a clinically significant impairment or distress) [20,

Conclusion

Based on the findings of the present study, the Persian YFAS-C is a valid instrument that can assist healthcare providers in assessing FA among Iranian adolescents. The validity and reliability of Persian YFAS-C were verified and supported by rigorous evaluation utilizing two major testing theories (i.e., CTT and IRT models). Additionally, FA was found to be prevalent among Iranian adolescents (12.1%) and was moderately associated with eating symptomatology and psychopathology. Consequently, healthcare providers should not ignore the issue of FA among adolescents.

What is already known on this subject?

The Yale Food Addiction Scale for Children (YFAS-C) is a commonly used instrument to assess food addiction for children and has been validated using classical test theory (CTT). The psychometric testing using CTT shows that YFAS-C is a promising instrument. However, it is unclear whether the YFAS-C has the same psychometric properties using another assessment theory (i.e., modern test theory) and it is unclear whether the YFAS-C has good properties in its Persian version.

What does this study add?

The study results indicated that the Persian YFAS-C has strong psychometric properties in both CTT and modern test theory results. With the robust psychometric properties, the Persian YFAS-C can assist clinicians in understanding the level of food addiction for Persian children and adolescents.