Table 1 Summary of results for psychiatric comorbidities included in the rapid review

Anxiety disorders (5 studies)

Anxiety disorders are most frequently comorbid condition reported in large population studies [8, 27]. Anxiety disorders often precede onset of EDs [28]. Temperamental factors specifically, anxiety sensitivity and experiential avoidance [29] appear to be associated with anxiety disorder and ED comorbidity

Generalised anxiety disorder (GAD) (2 studies)

Noted evidence of a potential genetic link between EDs and GAD; the presence of one significantly increases the likelihood of the other [8, 30]

There were particular links between fasting, excessive exercise, low BMI and comorbid GAD [30]

Social anxiety (4 studies)

Elevated rates of social anxiety across all ED diagnoses; highest in bulimia nervosa (BN), followed by binge eating disorder (BED) and AN-BP (AN—binge—purge subtype). Social anxiety was associated with more severe ED psychopathology and higher body weight [31] and acts as a barrier to accessing ED treatment [32]

Obsessive compulsive disorder (OCD) (5 studies)

The reported comorbidity rates of OCD and EDs were variable [33]. There is symptom overlap between OCD and EDs [34]; with evidence of OCD being related to more severe ED [34]; and treatment of one condition associated with symptom improvement in the other [35]. Further, comorbidity of OCD and EDs appears to be maintained by intrusive thoughts and perfectionism [36]

Major depressive disorder (MDD)/depression (10 studies)

Disordered eating may develop concurrently with depressive symptoms. Changes in frontal brain circuits seen in Depression, are also observed in EDs [37]. There is a strong relationship between MDD and EDs [AN, BN, BED and night eating syndrome (NES)]. However, results were mixed regarding the impact of MDD-ED comorbidity on treatment outcomes

Bipolar disorder (BD) (11 studies)

Notable rates of comorbidity between BD and EDs were reported, however evidence about the frequency of this association was mixed, ranging between 1.9% to as high as 35.8% [38,39,40]. BD was seen most in EDs which consist of a binge and/or purge symptom profile and comorbidity appears to impact on ED symptom severity, poorer daily and neuropsychological functioning

Personality disorders (PDs) (9 studies)

The association between any type of ED and PDs, was significantly higher than the general population [41]. For specific PDs, the proportions of paranoid, borderline, avoidant, dependant and obsessive–compulsive PD were significantly higher in EDs than the general population. The comorbidity between particular EDs and PDs appeared to be associated with common traits [i.e., impulsiveness of BN with borderline personality disorder (BPD), rigidity of AN with obsessive compulsive personality disorder (OCPD)]

Comorbidity was associated with greater distress and poorer outcomes. [41, 42]

Substance use disorders (SUD) (5 studies)

The prevalence rates of substance use in EDs were higher than the general population. Alcohol, caffeine and tobacco were the most frequently reported substances used in ED populations [43]. SUD was more frequently comorbid among individuals with binge/purge type EDs [44]

Psychosis and schizophrenia (3 studies)

A limited area of research; the majority focussed on NES–12% of participants with schizophrenia also met criteria for NES [45]. The actual comorbidity between psychotic disorders and ED remains unclear

Body dysmorphic disorder (BDD) (5 studies)

AN and BDD share similar psychopathology and both have a peak onset period in adolescence, although BDD development typically precedes AN [46]. The prevalence rates of BDD among individuals with AN are variable, however BDD contributes to greater symptom severity in individuals with AN

Attention deficit hyperactivity disorder (ADHD) (9 studies)

A positive association between ADHD and disordered eating, particularly between overeating and ADHD [47]. A twofold increased risk of ADHD in individuals with an ED [48] and studies have noted particularly strong associations between ADHD and BN [49, 50]. Children with ADHD were more like to experience an ED or binge, purge, or engage in restrictive behaviours above clinical threshold [51]

Autism spectrum disorder (ASD) (4 studies)

Prevalence rates of ASD are reported to be as high as 22.9% among individuals with EDs, compared with 2%, observed in the general population [52]. There is a high level of symptom cross-over between EDs and ASD. Symptoms of ASD are frequently exhibited by patients with AN [53, 54]. An assessment of common phenomena between ARFID and ASD in children found a shared symptom profile of eating difficulties, behavioural problems and sensory hypersensitivity beyond what is observed in children without ASD [55]

Post traumatic stress disorder (PTSD) (3 studies)

A broad range of prevalence rates between PTSD and EDs have been reported; between 16.1–22.7% for AN, 32.4–66.2% for BN and 24.02–31.6% for BED [56]. EDs might have a functional role to manage PTSD symptoms and reduce negative affect [57]

Suicidality (22 studies)

Suicide is one of the leading causes of death for individuals with EDs [58]. EDs were a significant risk factor for suicide, and evidence suggested a genetic association between the two [59, 60]

The risk for suicide attempts was higher for those with BN compared to other EDs, however, the risk of death by suicide was highest in AN [61, 62]

Non-suicidal self-injury (NSSI) (7 studies)

Up to one-third of patients with EDs report NSSI at some stage in their lifetime, with over one quarter having engaged in NSSI within the previous year [63]

Higher levels of impulsivity and emotional reactivity among patients with EDs were associated with concomitant NSSI [64, 65]. There were significant differences in the prevalence of NSSI across ED diagnoses, although patients with binge/purge subtype EDs were more likely to engage in poly-NSSI [66]