Comprehensive elucidation of resting-state functional connectivity in anorexia nervosa by a multicenter cross-sectional study.

BACKGROUND: Previous research on the changes in resting-state functional connectivity (rsFC) in anorexia nervosa (AN) has been limited by an insufficient sample size, which reduced the reliability of the results and made it difficult to set the whole brain as regions of interest (ROIs). METHODS: We analyzed functional magnetic resonance imaging data from 114 female AN patients and 135 healthy controls (HC) and obtained self-reported psychological scales, including eating disorder examination questionnaire 6.0. One hundred sixty-four cortical, subcortical, cerebellar, and network parcellation regions were considered as ROIs. We calculated the ROI-to-ROI rsFCs and performed group comparisons. RESULTS: Compared to HC, AN patients showed 12 stronger rsFCs mainly in regions containing dorsolateral prefrontal cortex (DLPFC), and 33 weaker rsFCs primarily in regions containing cerebellum, within temporal lobe, between posterior fusiform cortex and lateral part of visual network, and between anterior cingulate cortex (ACC) and thalamus (p < 0.01, false discovery rate [FDR] correction). Comparisons between AN subtypes showed that there were stronger rsFCs between right lingual gyrus and right supracalcarine cortex and between left temporal occipital fusiform cortex and medial part of visual network in the restricting type compared to the binge/purging type (p < 0.01, FDR correction). CONCLUSION: Stronger rsFCs in regions containing mainly DLPFC, and weaker rsFCs in regions containing primarily cerebellum, within temporal lobe, between posterior fusiform cortex and lateral part of visual network, and between ACC and thalamus, may represent categorical diagnostic markers discriminating AN patients from HC.

Systematic reduction of gray matter volume in anorexia nervosa, but relative enlargement with clinical symptoms in the prefrontal and posterior insular cortices: a multicenter neuroimaging study.

Although brain morphological abnormalities have been reported in anorexia nervosa (AN), the reliability and reproducibility of previous studies were limited due to insufficient sample sizes, which prevented exploratory analysis of the whole brain as opposed to regions of interest (ROIs). Objective was to identify brain morphological abnormalities in AN and the association with severity of AN by brain structural magnetic resonance imaging (MRI) in a multicenter study, and to conduct exploratory analysis of the whole brain. Here, we conducted a cross-sectional multicenter study using T1-weighted imaging (T1WI) data collected between May 2014 and February 2019 in Japan. We analyzed MRI data from 103 female AN patients (58 anorexia nervosa restricting type [ANR] and 45 anorexia nervosa binge-purging type [ANBP]) and 102 age-matched female healthy controls (HC). MRI data from five centers were preprocessed using the latest harmonization method to correct for intercenter differences. Gray matter volume (GMV) was calculated from T1WI data of all participants. Of the 205 participants, we obtained severity of eating disorder symptom scores from 179 participants, including 87 in the AN group (51 ANR, 36 ANBP) and 92 HC using the Eating Disorder Examination Questionnaire (EDE-Q) 6.0. GMV reduction were observed in the AN brain, including the bilateral cerebellum, middle and posterior cingulate gyrus, supplementary motor cortex, precentral gyrus medial segment, and thalamus. In addition, the orbitofrontal cortex (OFC), ventromedial prefrontal cortex (vmPFC), rostral anterior cingulate cortex (ACC), and posterior insula volumes showed positive correlations with severity of symptoms. This multicenter study was conducted with a large sample size to identify brain morphological abnormalities in AN. The findings provide a better understanding of the pathogenesis of AN and have potential for the development of brain imaging biomarkers of AN. Trial Registration: UMIN000017456. https://center6.umin.ac.jp/cgi-open-bin/icdr/ctr_view.cgi?recptno=R000019303 .

Persistence of gut dysbiosis in individuals with anorexia nervosa.

Recent evidence suggests a crucial role of the gut microbiota in the pathogenesis of anorexia nervosa (AN). In this study, we carried out a series of multiple analyses of the gut microbiota of hospitalized individuals with AN over three months using 16S or 23S rRNA-targeted reverse transcription-quantitative polymerase chain reaction (PCR) technology (YIF-SCAN®), which is highly sensitive and enables the precise quantification of viable microorganisms. Despite the weight gain and improvements in psychological features observed during treatment, individuals with AN exhibited persistent gut microbial dysbiosis over the three-month duration. Principal component analysis further underscored the distinct microbial profile of individuals with AN, compared with that of age-matched healthy women at all time points. Regarding the kinetics of bacterial detection, the detection rate of Lactiplantibacillus spp. significantly increased after inpatient treatment. Additionally, the elevation in the Bifidobacterium counts during inpatient treatment was significantly correlated with the subsequent body weight gain after one year. Collectively, these findings suggest that gut dysbiosis in individuals with AN may not be easily restored solely through weight gain, highlighting the potential of therapeutic interventions targeting microbiota via dietary modifications or live biotherapeutics.

Economic costs for outpatient treatment of eating disorders in Japan.

BACKGROUND: Few studies have examined the economic costs of outpatient care for eating disorders in Japan. This study aimed to clarify the reimbursement for outpatient treatment of eating disorders and compare the costs between the departments of Psychosomatic Medicine and Psychiatry in Japan. METHOD: A multicenter, prospective, observational study of patients with an eating disorder was conducted in the Psychosomatic Medicine departments of three centers and the Psychiatry departments of another three centers in Japan. We analyzed medical reimbursement for an outpatient revisit, time of clinical interviews, and the treatment outcome measured by the Eating Disorder Examination Questionnaire (EDE-Q) global scores and body mass index (BMI) at 3 months. Multivariate linear regression models were performed to adjust for covariates. RESULTS: This study included 188 patients in the Psychosomatic Medicine departments and 68 in the Psychiatry departments. The average reimbursement cost for an outpatient revisit was 4670 yen. Even after controlling for covariates, the Psychosomatic Medicine departments had lower reimbursement points per minute of interviews than the Psychiatry departments (coefficient = - 23.86; 95% confidence interval = - 32.09 to - 15.63; P < 0.001). In contrast, EDE-Q global scores and BMI at 3 months were not significantly different between these departments. CONCLUSIONS: This study clarifies the economic costs of treating outpatients with eating disorders in Japan. The medical reimbursement points per interview minute were lower in Psychosomatic Medicine departments than in Psychiatry departments, while there were no apparent differences in the treatment outcomes. Addressing this issue is necessary to provide an adequate healthcare system for patients with eating disorders in Japan.

This study examined the cost of outpatient care for eating disorders in Japan, comparing treatment costs between the Psychosomatic Medicine and Psychiatry departments. The actual cost of outpatient care for eating disorders in Japan was clarified. The results indicate that Psychosomatic Medicine departments have lower reimbursement points per interview time compared to the Psychiatry departments, but there were no noticeable differences in treatment outcomes between the two. This highlights the need to address this cost difference to improve the healthcare system for patients with eating disorders in Japan.

A multi-center, randomized, parallel-group study to compare the efficacy of enhanced cognitive behavior therapy (CBT-E) with treatment as usual (TAU) for anorexia nervosa: study protocol.

BACKGROUND: The superiority of Enhanced Cognitive Behavior Therapy (CBT-E) with regard to weight gain and improvement of psychopathology of eating disorders for patients with anorexia nervosa (AN) over other psychotherapies and treatment as usual (TAU) has not been demonstrated in randomized controlled trials (RCTs). However, a previous RCT showed that patients with AN whose baseline body mass index (BMI) was less than 17.5 kg/m2 gained more weight when treated with CBT-E than with other psychotherapies. The aim of the study is to compare the efficacy of CBT-E and TAU for patients with AN. It was hypothesized that CBT-E would be superior to TAU, at least in terms of weight gain, as most patients with AN are likely to have a BMI lower than 17.5 kg/m2. METHODS/DESIGN: A randomized parallel-group multicenter trial will be conducted in three teaching hospitals in Japan between January 2023 and March 2026. Patients with DSM-5 AN, aged 16 years and older, with a BMI equal to or above 14.0 and below 18.5 will be eligible to participate. 56 patients will be randomly and evenly assigned to two intervention groups (CBT-E and TAU). Those assigned to CBT-E will be offered 25-40 sessions in accordance with their initial BMI. Patients assigned to TAU will have at least one session every 2 weeks, with the number of sessions and treatment period not fixed in advance. The primary outcome is BMI at 40 weeks after treatment initiation. The secondary outcomes are the results from the Japanese version of the Eating Disorder Examination Questionnaire and Clinical Impairment Assessment questionnaire to measure eating disorder psychopathology and psychological impairment. The follow-up assessment will be performed 6 months after the 40-week assessment. DISCUSSION: This multi-center randomized controlled study will probably evaluate the efficacy of CBT-E compared with TAU for patients with more severe AN than in previous studies since Japanese patients are likely to have a lower BMI than those in Western countries. While it may be difficult to generalize the results of a study conducted in Japan, it would be valuable to clarify the efficacy of CBT-E as a treatment package. TRIAL REGISTRATION: UMIN, UMIN000048847. Registered 12 Sep 2022.

Effects of integrated hospital treatment on the default mode, salience, and frontal-parietal networks in anorexia nervosa: A longitudinal resting-state functional magnetic resonance imaging study.

The psychopathology of patients with anorexia nervosa has been hypothesized to involve inappropriate self-referential processing, disturbed interoceptive awareness, and excessive cognitive control, including distorted self-concern, disregard of their own starvation state, and extreme weight-control behavior. We hypothesized that the resting-state brain networks, including the default mode, salience and frontal-parietal networks, might be altered in such patients, and that treatment might normalize neural functional connectivity, with improvement of inappropriate self-cognition. We measured resting-state functional magnetic resonance images from 18 patients with anorexia nervosa and 18 healthy subjects before and after integrated hospital treatment (nourishment and psychological therapy). The default mode, salience, and frontal-parietal networks were examined using independent component analysis. Body mass index and psychometric measurements significantly improved after treatment. Before treatment, default mode network functional connectivity in the retrosplenial cortex and salience network functional connectivity in the ventral anterior insula and rostral anterior cingulate cortex were decreased in anorexia nervosa patients compared with those in controls. Interpersonal distrust was negatively correlated with salience network functional connectivity in the rostral anterior cingulate cortex. Default mode network functional connectivity in the posterior insula and frontal-parietal network functional connectivity in the angular gyrus were increased in anorexia nervosa patients compared with those in controls. Comparison between pre- and post-treatment images from patients with anorexia nervosa exhibited significant increases in default mode network functional connectivity in the hippocampus and retrosplenial cortex, and salience network functional connectivity in the dorsal anterior insula following treatment. Frontal-parietal network functional connectivity in the angular cortex showed no significant changes. The findings revealed that treatment altered the functional connectivity in several parts of default mode and salience networks in patients with anorexia nervosa. These alterations of neural function might be associated with improvement of self-referential processing and coping with sensations of discomfort following treatment for anorexia nervosa.

Assessment and Treatment of Eating Disorders.

Eating disorders are serious psychiatric conditions in terms of chronicity and have the highest mortality rate among psychiatric disorders. The assessment and treatment of eating disorders are also challenging, due to patients' denial of their illness and reluctance for change. Despite a large number of previous assessment and treatment studies, new strategies to overcome these difficulties are still needed. This study casts light on four aspects; involvement of the brain's reward system, stages of change in relationship with motivation, refeeding syndrome during renourishment, and gut microbiota changes relating to chronicity. Further studies relating to these aspects are encouraged.

Cardiopulmonary exercise testing for patients with anorexia nervosa: a case-control study.

PURPOSE: Patients with anorexia nervosa (AN) require appropriate nutrient therapy and physical activity management. Eating disorder treatment guidelines do not include safe, evidence-based intensity criteria for exercise. This study used cardiopulmonary exercise testing (CPX) to evaluate the exercise tolerance of patients with AN. METHODS: CPX was performed with 14 female patients with AN admitted to a specialized eating disorder unit between 2015 and 2019. Their anaerobic threshold (AT) was determined by assessing their exercise tolerance using CPX and compared with 14 healthy controls (HC). The metabolic equivalents (AT-METS) were compared when AT was reached. We examined factors related to AT (AN-AT) in the AN group, including age, body mass index (BMI), previous lowest weight, minimum BMI, past duration of BMI < 15, exercise history, and ΔHR (heart rate at the AT-resting heart rate). RESULTS: The AT of the AN group (BMI: 15.7 [Mean] ± 1.8 standard deviation [SD]) was significantly lower than that of the HC group (BMI: 19.7 ± 1.8) (AN: 10.0 ± 1.8 vs. HC: 15.2 ± 3.0 ml/kg/min, P < 0.001). AT-METS was also significantly lower in the AN group than in the HC group (AN: 2.9 ± 0.52 vs. HC: 4.4 ± 0.91, P < 0.001). AN-AT was highly influenced by ΔHR. CONCLUSIONS: This study showed that AT and AT-METS were lower in patients with AN than in HC. Patients with AN should be prescribed light-intensity aerobic exercise, and the current findings may help develop future physical management guidelines for patients with AN. LEVEL OF EVIDENCE: III: Evidence obtained from case-control analytic studies.

Potential impact of the COVID-19 pandemic on japanese patients with eating disorders -a cross-sectional study.

BACKGROUND: The COVID-19 pandemic and associated lockdown had a considerable impact on eating disorders (EDs). We evaluated the clinical features of Japanese ED patients before and after the first COVID-19 outbreak-related state of emergency (April 7, 2020). METHODS: We studied 148 patients who were divided into two groups based on when they arrived at our clinic: before (Before group: n = 86) or after (After group: n = 62) the start of the first state of emergency. All patients completed the Japanese versions of the Eating Disorder Inventory (EDI) and Parental Bonding Instrument (PBI). RESULTS: The After group was substantially younger than the Before group (p = .0187). Regardless of the ED type, patients who developed an ED during the first state of emergency tended to be significantly younger than those who developed one before. Differences in EDI characteristics were observed between the two groups. The PBI care subscale was notably higher (p = .0177) in the After group. The PBI maternal care subscale was the only statistically significant factor associated with age (ß = -0.35, p < .0001). CONCLUSIONS: Home confinement associated with the COVID-19 pandemic and the ensuing increase in parent-child closeness may have influenced the decreased age of ED patients at their initial consultation. Treatment interventions should consider the differences in the clinical features of EDs.

Dietary tryptophan, tyrosine, and phenylalanine depletion induce reduced food intake and behavioral alterations in mice.

Important precursors of monoaminergic neurotransmitters, dietary tryptophan (TRP), tyrosine, and phenylalanine (all referred to as TTP), play crucial roles in a wide range of behavioral and emotional functions. In the current study, we investigated whether diets devoid of TTP or diets deficient in TRP alone can affect body weight, behavioral characteristics, and gut microbiota, by comparing mice fed on these amino acids-depleted diets to mice fed on diets containing regular levels of amino acids. Both dietary TTP- and TRP-deprived animals showed a reduction in food intake and body weight. In behavioral analyses, the mice fed TTP-deprived diets were more active than mice fed diets containing regular levels of amino acids. The TRP-deprived group exhibited a reduction in serum TRP levels, concomitant with a decrease in serotonin and 5-hydroxyindoleacetic acid levels in some regions of the brain. The TTP-deprived group showed a reduction in TTP levels in the serum, concomitant with decreases in both phenylalanine and tyrosine levels in the hippocampus, as well as serotonin, norepinephrine, and dopamine concentrations in some regions of the brain. Regarding the effects of TRP or TTP deprivation on gut microbial ecology, the relative abundance of genus Roseburia was significantly reduced in the TTP-deprived group than in the dietary restriction control group. Interestingly, TTP was found even in the feces of mice fed TTP- and TRP-deficient diets, suggesting that TTP is produced by microbial or enzymatic digestion of the host-derived proteins. However, microbe generated TTP did not compensate for the systemic TTP deficiency induced by the lack of dietary TTP intake. Collectively, these results indicate that chronic dietary TTP deprivation induces decreased monoamines and their metabolites in a brain region-specific manner. The altered activities of the monoaminergic systems may contribute to increased locomotor activity.

Eating Disorder Neuroimaging Initiative (EDNI): a multicentre prospective cohort study protocol for elucidating the neural effects of cognitive-behavioural therapy for eating disorders.

INTRODUCTION: Anorexia nervosa is a refractory psychiatric disorder with a mortality rate of 5.9% and standardised mortality ratio of 5.35, which is much higher than other psychiatric disorders. The standardised mortality ratio of bulimia nervosa is 1.49; however, it is characterised by suicidality resulting in a shorter time to death. While there is no current validated drug treatment for eating disorders in Japan, cognitive-behavioural therapy (CBT) is a well-established and commonly used treatment. CBT is also recommended in the Japanese Guidelines for the Treatment of Eating Disorders (2012) and has been covered by insurance since 2018. However, the neural mechanisms responsible for the effect of CBT have not been elucidated, and the use of biomarkers such as neuroimaging data would be beneficial. METHODS AND ANALYSIS: The Eating Disorder Neuroimaging Initiative is a multisite prospective cohort study. We will longitudinally collect data from 72 patients with eating disorders (anorexia nervosa and bulimia nervosa) and 70 controls. Data will be collected at baseline, after 21-41 sessions of CBT and 12 months later. We will assess longitudinal changes in neural circuit function, clinical data, gene expression and psychological measures by therapeutic intervention and analyse the relationship among them using machine learning methods. ETHICS AND DISSEMINATION: The study was approved by The Ethical Committee of the National Center of Neurology and Psychiatry (A2019-072). We will obtain written informed consent from all patients who participate in the study after they had been fully informed about the study protocol. All imaging, demographic and clinical data are shared between the participating sites and will be made publicly available in 2024. TRIAL REGISTRATION NUMBER: UMIN000039841.

Metabolomics profile of Japanese female patients with restricting-type anorexia nervosa.

In this study, the serum metabolic profiles of 10 female patients with restricting type anorexia nervosa (ANR) were compared to those of 10 age-matched healthy female controls. While the levels of amino acids were lower among the patients than among the controls, the levels of uremic toxins, including p-cresyl sulfate (PCS), indole-3-acetic acid, and phenyl sulfate, were higher in ANR patients. The serum PCS levels correlated positively with the abundance of the Clostridium coccoides group or the C. leptum subgroup in the feces of patients, but not in those of controls. Collectively, these results indicate that the serum metabolic profiles of patients with ANR differ from those of healthy women in terms of both decreased amino acid levels and increased uremic toxins. Gut microbes including C. coccoides or C. leptum may be involved in such an increase in uremic toxins.

Psychometric properties of the fear of food measure in Japanese women.

PURPOSE: The aim of the present study was to investigate the psychometric properties of the fear of food measure (FOFM) in Japanese women. METHODS: This study was a cross-sectional, observational, and multicenter study conducted at the University of Tokyo and Kyushu University. Participants were comprised of 169 healthy women and 149 patients with eating disorders. First, the present study explored the factor structure of FOFM in Japanese women using exploratory factor analyses. Then, the Cronbach's alpha and McDonald's omega were calculated to assess reliability. Concurrent validity was examined by calculating correlation coefficients with the Eating Attitudes Test, negative affect of Positive and Negative Affect Schedule, and Hospital Anxiety and Depression Scale. Additionally, the Wilcoxon rank-sum test was used to compare scores between the healthy control and patient group. RESULTS: The final model had four subscales. The subscales, thus, had high reliability and showed significant positive correlations with the questionnaires. The scores of subscales in the patient group were significantly higher than those in the healthy control group. CONCLUSIONS: The FOFM had a four-factor structure in Japanese women. Its reliability and validity were verified and it could be used as a tool to assess fear of food. LEVEL OF EVIDENCE: III, case-control analytic study.

Development of a new Japanese version of the Clinical Impairment Assessment Questionnaire.

BACKGROUND: The Clinical Impairment Assessment questionnaire (CIA) is used to measure the severity of psychosocial impairment in patients with eating disorders. The purpose of the present study was to develop a new Japanese version of the CIA (CIA-J) and to evaluate its reliability and validity. METHODS: We translated the sixteen items of the CIA into Japanese, back-translated them into English, and had them verified by a native English speaking professional editor. Participants were 152 Japanese-speaking patients (30.4 ± 10.6 years) under treatment for eating disorders and 173 healthy controls (29.5 ± 8.3 years). In addition to the CIA-J, the participants were asked to answer the Eating Attitudes Test (EAT26), The Positive and Negative Affect Schedule (PANAS), and the Hospital Anxiety and Depression Scale (HADS). We performed confirmatory factor analyses to evaluate the factor structure, calculated the Cronbach's alphas of the CIA-J to assess the reliability, and calculated the correlation coefficients between the CIA-J score and those of EAT26, PANAS, and HADS to assess concurrent validity. We also used a Kruskal-Wallis test followed by Steel-Dwass test to compare the scores of the subtypes of eating disorders and the healthy control group. RESULTS: A three-factor structure was obtained, similar to the original version. The Cronbach's alphas of both the global and subscale scores of the CIA-J were high. The CIA-J had significant positive correlations with the EAT26, the negative affect subscale of the PANAS, and the HADS. The global and subscale scores for all subtypes of eating disorders were significantly higher than those of the healthy control group. CONCLUSIONS: The CIA-J was determined to be reliable and valid for assessing the severity of psychosocial impairment in patients with eating disorders.

Correction to: Very long chain fatty acids are an important marker of nutritional status in patients with anorexia nervosa: a case control study.

[This corrects the article DOI: 10.1186/s13030-020-00186-8.].

Very long chain fatty acids are an important marker of nutritional status in patients with anorexia nervosa: a case control study.

BACKGROUND: Anorexia nervosa (AN) is a disease resulting in extreme weight loss. It is caused by multiple factors, including psychosocial, environmental, and genetic factors. A genetic abnormality affecting lipid metabolism has been recently reported in patients with AN. However, it is unknown whether lipid metabolism abnormalities in AN are caused by eating behavior, undernutrition, and/or genetic factors. The meaning of lipid metabolism in AN remains unclear. In particular, differences in the profiles of very long-chain fatty acids (VLCFAs) in patients with various types of AN have not been studied. This study aimed to determine changes to the fatty acid profile over a 3-month period, specifically that of long-chain fatty acids (LCFAs) and VLCFAs in patients with various types of AN. METHODS: We evaluated 69 female patients with AN, subclassified as AN-restricting type (AN-R) and AN-Binge-Eating/Purging type (AN-BP). On admission and after 3 months of treatment, height, weight, body mass index, plasma and serum parameters, and plasma fatty acid concentrations were measured in all patients. The control group included 25 healthy, age-matched women. Comparisons between the groups were made using one-way ANOVA, while those between the various parameters at admission and after 3 months within each group were made using the Wilcoxon signed rank test. RESULTS: On admission, the AN-R and the AN-BP groups had significantly higher levels of 18-24C and > 14C fatty acids (LCFAs and VLCFAs, respectively) than the control group. After 3 months of treatment, both groups showed high levels of 14-24C fatty acids. The levels of VLCFAs (C22:0 and C24:0) and LCFA (C18:3) after 3 months of treatment remained high in both AN groups relative to the control group. CONCLUSIONS: Eating behaviors appear to be associated with levels of LCFAs. Lipid metabolism abnormalities under conditions of starvation in AN might have a genetic basis and appear to be associated with VLCFA (C22:0 and C24:0) and LCFA (C18:3) levels.

Dietary delivery of acetate to the colon using acylated starches as a carrier exerts anxiolytic effects in mice.

Recently, short-chain fatty acids (SCFA) have been shown to play an important role in mediating the gut-brain interaction and thereby participate in the patho-physiological process of stress-related disorders. In the current study, we examined whether SCFA generated in the lower gut affects host metabolic and behavioral characteristics. To determine this, we used special diets containing acylated starches that can reach the colon without being absorbed in the upper gastrointestinal tract of male mice. The delivery of SCFA to the colon using this method induced a substantial increase in acetate, butyrate, and propionate in the cecum. Moreover, the diets containing acylated starches also decreased microbial diversity in the cecum, concomitant with a significant impact on microbial composition. In marble-burying (MB) tests, the mice that consumed diets containing acetylated starches showed a decrease in anxiety-like behavior compared with the mice that consumed diets containing either butyrylated or propionylated starches. Cecal acetate contents were significantly associated with anxiety-like behaviors when evaluated by elevated plus-maze and MB tests. Collectively, these results indicate that gut acetate elevation of a dietary origin may exert anxiolytic effects on behavioral phenotypes of the host.

Effectiveness of enhanced cognitive behavior therapy for bulimia nervosa in Japan: a randomized controlled trial protocol.

BACKGROUND: The effectiveness of psychotherapeutic interventions for eating disorders (EDs) is widely studied in Europe, North America, and Australia/New Zealand. However, few controlled studies and no randomized controlled trials (RCTs) have been conducted in Japan despite the relatively high prevalence of EDs in the Japanese population. The aim of this study is to evaluate the effect of enhanced cognitive behavior therapy (CBT-E), an evidence-supported ED-focused form of cognitive behavior therapy (CBT), for the treatment of bulimia nervosa (BN) in Japan. METHODS/DESIGN: This multicenter RCT will compare CBT-E with treatment as usual (TAU), which is widely used in Japan. A group of 140 adult outpatients with a Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5) diagnosis of BN, ≥18 years of age, a body mass index (BMI) > 17.5 and < 40 kg/m2 will be randomly assigned to CBT-E or TAU. Participants will be stratified by intervention site and BN severity. CBT-E participants will receive 20 sessions of focused form CBT-E for 20 weeks. Those in the TAU group will receive routine treatment provided by specialists. Assessment will be performed in a blinded manner prior to the start of treatment, after 6 weeks of treatment, at the end of treatment (20 weeks), and at follow-up at 40 and 80 weeks after the start of treatment. The primary outcome is the remission of BN, defined by the absence, in the previous 4 weeks, of symptoms required to meet the DSM-5 criteria for a diagnosis of BN. Secondary outcomes include the levels of ED psychopathology and impairment due to the ED, anxiety, depression, family function, and satisfaction with treatment. DISCUSSION: This will be the first RCT conducted in Japan to compare CBT-E and TAU for the treatment of BN. If CBT-E is found to be more effective than TAU, then the evidence would support its wider use for patients with BN in Japan. Because it is possible to train therapists who do not possess extensive specialist experience, wider use is also likely to be practically feasible. In addition, demonstrating the effectiveness of CBT-E in Japan would demonstrate that it could be successfully extended to additional world cultures and regions. TRIAL REGISTRATION: UMIN, UMIN000031625. Registered 7 Mar 2018.