Both conditions also show similar alterations in the structure and function of brain regions involved in social perception.
"Autism is diagnosed more often in males," said Dr Bonnie Auyeung, a member of the research team at Cambridge University's Autism Research Centre. "This new research suggests that a proportion of females with autism may be being overlooked or misdiagnosed, because they present to clinics with anorexia."
Researchers studied 66 girls age 12-18 who had been diagnosed with anorexia but not autism.
They compared them to over 1,600 typical teenagers in the same age range, and measured their autistic traits using the Autism Spectrum Quotient (AQ), their ‘systemizing’ using the Systemising Quotient (SQ), and their empathy using the Empathy Quotient (EQ).
On the AQ, girls with anorexia were five times as likely as typical teenagers to score in the range that people with autism score in. More than half of the girls with anorexia showed the "broader autism phenotype," compared to 15 percent of typical girls.
Girls with anorexia also scored higher than typical girls on the SQ, which measures how strong a person's interest in repeating patterns and predictable rule-based systems. Paralleling autism, girls with anorexia also showed lower empathy than typical girls.
"Traditionally, anorexia has been viewed purely as an eating disorder. This is quite reasonable, since the girl’s dangerously low weight, and their risk of malnutrition or even death has to be the highest priority," said lead author Simon Baron-Cohen.
"But this new research is suggesting that underlying the surface behaviour, the mind of a person with anorexia may share a lot with the mind of a person with autism," Baron-Cohen said. "In both conditions, there is a strong interest in systems. In girls with anorexia, they have latched onto a system that concerns body weight, shape, and food intake."
"Acknowledging that some patients with anorexia may also have a raised number of autistic traits and a love of systems gives us new possibilities for intervention and management. For example, shifting their interest away from body weight and dieting on to a different but equally systematic topic may be helpful."