Dieting is not unusual, although many of us will still reach for the chocolate on a stressful day and enjoy it, perhaps with a half-hearted plan to resume the diet at another time. Individuals with anorexia nervosa (AN) are unlikely to have such a relaxed reaction. First described by 19th century medical reports,¹ AN is characterised by significant weight loss driven by an intense fear of weight gain. These symptoms can also occur in individuals who lose a significant amount of weight in a short time, but are not underweight, a diagnosis referred to as atypical AN. While the cause of AN is unknown, there are likely to be biological, psychosocial and environmental factors at play, as risk factors include female gender, residence in a developed country, genetic heritability and personality traits such as perfectionism.² Dieting is also a major risk factor, especially in the context of increasing rates of obesity with a focus on weight reduction and physical activity.³

In contrast to AN, adolescents with bulimia nervosa (BN) experience recurrent episodes of binge eating and restriction, exercise or purging, but they do not lose weight. Binge eating disorder (BED) is characterised by recurrent episodes of binge eating without the compensatory behaviours.

A newly described heterogenous eating disorder, avoidant restrictive food intake disorder (ARFID), refers to a significant eating disturbance that is not driven by concern over body shape or weight, unlike AN or BN. Adolescents with ARFID restrict their food intake for a variety of reasons, such as sensory issues, lack of interest, or fear of choking or vomiting. Table 1 shows the diagnostic criteria for these eating disorders.⁴

The rates of eating disorders vary depending on whether they are population, community or clinic-based samples. Recent studies suggest that lifetime prevalence rates for AN range from 0.3–1.7 per cent, 0.8–0.9 per cent for BN, and 1.6–2.3 per cent for BED. Subthreshold eating disorders occur at much higher rates.⁵,⁶ ARFID has not been as well studied. Despite the different aetiologies, each of these disorders has serious medical consequences.

Table 1. Diagnostic criteria for AN, ARFID, BN and BED.

Complications of eating disorders

While eating disorders can occur in adulthood, they commonly present in the adolescent years, a significant time for growth and development. Disordered eating behaviours can lead to malnutrition or overweight/obesity, affecting multiple organ systems and impacting short and long-term health. The impacts on the major organ systems are discussed below. Typical presentations to the O&G include menstrual disturbance and concerns about fertility.

Menstrual concerns and pubertal development

There is a clear relationship between significant weight loss, excessive exercise and low BMI in AN and amenorrhoea, with suppression of the hypothalamic-pituitary-ovarian axis and low oestrogen levels. On the other hand, BN and BED can also be associated with irregular menstruation and polycystic ovarian syndrome.⁷ Delayed growth and delayed puberty are common features, especially when restrictive eating disorders such as AN and ARFID occur during the peripubertal period and early adolescence.

Bone health

Restrictive eating disorders pose a significant threat to long-term bone health, as the greatest increase in bone mineral density occurs during the adolescent years. Oestrogen deficiency, hypercortisolaemia, changes in growth hormone, and IGF-1 occurring in malnutrition affect bone formation, as well as playing a role in bone resorption. The best predictive factor of decreased bone density is the duration of amenorrhoea.⁸ Fifty per cent of adolescents with AN have bone mineral density values of greater than one standard deviation (1 SD) below their healthy peers.⁹ Up to 30 per cent of adolescent girls and adult women report having sustained a fracture. In addition, women of normal weight with BN were found to have lower spinal bone mineral density compared to their healthy peers, suggesting that factors other than weight loss influence bone metabolism.¹⁰

Treatment of amenorrhoea and low bone density should focus on weight gain and restoration of menstrual function, as well as optimisation of calcium and vitamin D. Studies suggest that oestrogen replacement using the combined oral contraceptive pill in adolescents and adults with AN is not effective in improving bone density. There is some research suggesting that transdermal physiologic oestrogen (17β oestradiol) may be useful in increasing bone mineral density, although complete catch up does not occur.¹¹ Bisphosphonates have been effective in improving bone density in adults, however, concerns about long half-lives and potential for teratogenicity limit its use in adolescents and women of childbearing age.

Reproductive health and obstetric concerns

Research on how fertility is affected by eating disorders (even when in remission) is mixed, with clinical samples reporting lower rates of pregnancy compared to matched controls.¹² However, population-based studies indicate no difference between rates of pregnancy and infertility treatment in women with a history of AN compared to the normal population.¹³ There is also a complex association between BN, BED, polycystic ovary syndrome, obesity and infertility.¹⁴ Women with BED may have a greater risk of miscarriage.¹²

A number of large cohort studies have shown that the risk of unplanned pregnancy is higher in women with AN and BN, despite the high prevalence of menstrual disturbance.¹² Negative feelings regarding pregnancy are common in women with eating disorders.¹⁵ Remission can occur during pregnancy, but relapse may also be triggered.¹⁶ Women with BN and BED risk excessive gestational weight gain.¹⁷

Studies also show that women with eating disorders experience increased perinatal problems, including postnatal depression and relapse. Infants born to mothers with an eating disorder are more likely to be born prematurely, have lower birth weights, lower Apgar scores and feeding difficulties.¹⁸

Cardiac

Common findings in restrictive eating disorders include bradycardia, postural tachycardia, hypotension and postural hypotension. With progressive malnutrition, structural, functional and conduction abnormalities occur more frequently. About half of deaths in AN can be attributed to cardiovascular causes, such as tachyarrhythmias and cardiac failure. Misuse of laxatives, diuretics or purging can lead to electrolyte abnormalities, contributing to predisposition for arrhythmias.¹⁹ Metabolic complications and risk of cardiovascular disease are complications of obesity as a result of BED.

Neurological

Patients with eating disorders often complain about headaches and difficulties in concentration. With increasing malnutrition, they can present with psychomotor retardation and inflexible thinking styles. Neuroimaging studies, mostly in patients with AN, report a reduction in both grey and white matter. Studies show that many of these changes were reversible with weight gain. There were similar findings in patients with BN, although less pronounced. Functional brain imaging studies have also shown changes in neural circuitry related to cognitive control, reward and emotion processing. The impact of BED on the brain is still being studied.²⁰

Treatment

Given the significant long-term complications of eating disorders, treatment must focus on improved nutritional status in all eating disorders and weight recovery in restrictive disorders.

Family-based treatment (FBT) has the strongest evidence base for treatment of adolescent AN.²¹ The aim of FBT is to remove control from the adolescent by tasking the parents with the role of re-feeding.The FBT therapist coaches the parents to support and supervise the adolescent in eating meals and snacks to enable weight gain or maintenance. Due to the success of FBT in adolescent AN, modified forms of FBT have been adapted for use in adults.²² FBT is also used for adolescents with ARFID because of its success in achieving weight gain, although there is currently little data on efficacy given the newness of the disorder.

First-line treatment for BN in adults is cognitive based therapy (CBT).²³ CBT aims to normalise eating patterns and reduce binge-purge episodes. In adolescent BN, both FBT and CBT are effective treatment modalities.²⁴ CBT can also be delivered through self-help books when professional therapy is unobtainable. Selective serotonin reuptake inhibitors (SSRIs), particularly high dose (60mg) fluoxetine, may also be used as an adjunct to therapy in patients with BN.²³

There is empirical evidence for the use of CBT in BEDs in adults. Pharmacological measures include SSRIs and topiramate may confer additional benefit.²³ The management of co-morbid obesity also needs to be taken into account, however, focus only on weight control measures such as diet and exercise may exacerbate restriction, binge eating and purging.

Inpatient treatment has been generally reserved for management of haemodynamic instability, electrolyte abnormalities or suicidality.

Conclusion

Eating disorders are serious mental illnesses that can present at any age, but most commonly in adolescents and young women. These disorders are associated with multiple medical complications and high rates of morbidity and mortality. Early identification and treatment is crucial for better outcomes for young women and their offspring. Young women often present to O&Gs for menstrual disturbance or fertility concerns. This means that O&Gs are well placed to enquire about disordered eating and weight-related behaviours, counsel for pregnancy and refer to, or collaborate with, multidisciplinary teams for treatment.

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