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First studies reveal the occurrence of 'chew and spit' behaviour

2 December 2019
Study led by Phillip Aouad from the School of Psychology has laid out how widespread this disordered eating behaviour is. While low among adults, up to 12 percent of teenagers report episodes of chewing and spitting out food.

The prevalence of the disordered eating behaviour known as ‘chew and spit’ among teenagers has been determined for the first time, thanks to a large-scale study analysed by psychologists at the University of Sydney.

Chew and spit, as the name suggests, is the pathological chewing of food and spitting it out before swallowing. It can often be used as a weight management technique by people with eating disorders. The behaviour, which is not recognised as a separate disorder, can follow patients across different types of eating disorders, including bulimia and anorexia nervosa.

An earlier study by the same team into the behaviour found a prevalence in adults of 0.4 percent, slightly below the range for disorders such as bulimia or anorexia, which occur in about 1 to 2 percent of the population.

However, the current study found that chew-and-spit behaviour can occur in as many as 12 percent of adolescents. The study is published this week in Eating Disorders: The Journal of Treatment & Prevention.

“The results surprised us,” said lead author Phillip Aouad who is completing his doctorate in the School of Psychology. “While we expected a higher prevalence in adolescents, the fairly high result is cause for concern and warrants further investigation.”

Phillip Aouad.

Phillip Aouad.

He said that while the numbers in the wider adult population are relatively low, prevalence in adolescents (particularly girls) seem to be significantly higher, which is of clinical concern.

Mr Aouad in particular is worried that the behaviour is not being screened by clinicians as it is not a recognised as a separate symptom by the American Psychiatric Association Diagnostic and Statistical Manual (DSM), the clinical ‘bible’ of psychiatric and psychological disorders.

“If chew and spit is not recognised as a formal symptom in the clinical literature, it makes it harder to identify and treat,” Mr Aouad said.

The American Psychiatric Association removed chew-and-spit behaviour as a recognised symptom from DSM-5 in 2013 because it was believed to not be prevalent. However, the current studies suggest that is not the case.

“Such a high prevalence rate in adolescents is indicative of disordered eating behaviour that cannot be ignored,” Mr Aouad said. “Without bringing this into clinical awareness, clinicians are unlikely to screen for the behaviour.”

Given that the ramifications of the behaviour are still not well understood, he said, future studies are required to examine adverse impacts.

The study on adolescents published this week involved a longitudinal survey of 5111 high-school students aged 11 to 19 in New South Wales, Australia. The base study of adults, published in 2017 in the International Journal of Eating Disorders, involved surveying 3047 individuals who were aged 16 or older in South Australia.

As well as identify the base-line prevalence of the behaviour among adolescents, the study also found that chew-and-spit behaviour was associated with increased psychological distress and lower health-related quality of life.

Further it found an association with overeating, fasting, weight and shape concerns, laxative abuse and vomiting. Chew-and-spit behaviour was not significantly associated with either strict dieting or exercise, the study found.

For adolescents, the 12.2 percent prevalence was for at least one to three episodes of chew-and-spit within the past 28 days. More intense exhibitions of the behaviour were also recorded. Of all respondents, 7.7 percent reported one to three episodes; 2.5 percent reported four to seven episodes; while 2.1 per cent reported eight or more episodes.

The study also recorded a distinct gender breakdown. For the adolescent cohort studied, 10.2 percent of males reported episodes of chew-and-spit behaviour, whereas 15.1 percent of females reported the behaviour. The study reported responses from 35 people of other gender, with eight (22.9 percent) reporting chew-and-spit behaviour (a statistically small sample).

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If you are struggling, it is recommended you speak to your primary care physician and obtain a referral to a psychologist or psychiatrist.


Two of the authors, Stephen Touyz and Phillipa Hay, receive publishing royalties for contributions on eating disorders. Stephen Touyz has received travel grants, consulting fees and grant funding from Shire Pharmaceuticals. He has also chaired the Australian Advisory Board on Binge Eating Disorder and provided commissioned requests. Phillipa Hay has received royalties from Oxford University Press and receives sessional fees and lecture fees from the Australian Medical Council, Therapeutic Guidelines publication and the NSW Institute of Psychiatry. She is also a member of the World Health Organization Working Group on Feeding and Eating Disorders for the Revision of ICD-10 Mental and Behavioural Disorders. She has received an honorarium from Shire Pharmaceuticals for a commissioned report.

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