Children as young as four attended health services for eating disorders in Wales last year, new figures show.
At least one four-year-old girl and at least one five-year-old boy attended child and adolescent mental health services (CAMHS) for unspecified eating disorders in south Wales in 2015-16.
Charity Beat said disorders "can affect anyone, regardless of age".
The Welsh Government said triggers for eating disorders were "complex" but services were "in place".
A record number of teenagers ended up in Welsh hospitals after being diagnosed with an eating disorder in 2014-15.
Details from Cwm Taf University Health Board, which hosts CAMHS across south Wales, showed the number of new patients aged under 18 attending its services for eating disorders rose from under 43 to 236 - a 450% increase - between 2014-15 and 2016-17.
The number of new attendances for boys in the area during that period grew by at least 600%.
For girls, the figure rose by 400% over the three years, according to the numbers, obtained via a Freedom of Information request.
The precise number of boys and girl in each age group could not be disclosed for fear it might identify some patients, but the majority were aged 12-17.
It is not clear how many were then diagnosed.
Equivalent figures for the rest of Wales have not been released. However, Powys Teaching Health Board figures showed the number of children who received outpatient treatment for eating disorders hit a four-year low in 2015-16.
Calls have previously been made for a specialist easting disorder unit in Wales.
Abi Davies, 25, of Neath, who developed anorexia when she was nine, said she was "surprised and alarmed" children so young were presenting with disorders.
"I think people at a younger age are [now] more aware of the world, they are more aware of social aspects of life.
"There is a biological factor - there's talk that there is a genetic link, as well. When you initially hear four and five-year-olds it's quite startling.
"But when you look at the factors behind it, maybe it's something we are going to be seeing more and more of."
To find our more about Ms Davies' fight with anorexia, click here.
What is an eating disorder?
An eating disorder is a medical diagnosis of a particular eating problem. You might be diagnosed by a doctor or a psychiatrist. These are the most common eating disorders:
- Bulimia nervosa: when a person goes through periods of binge eating and is then deliberately sick or uses laxatives (medication to help empty the bowels) to try to control their weight.
- Anorexia nervosa: when a person tries to keep their weight as low as possible; for example, by starving themselves or exercising excessively.
- Binge eating disorder: when a person feels compelled to overeat large amounts of food in a short space of time.
- Other specified feeding or eating disorder (OSFED) covers an eating disorder which does not fit into any other categories and may include a mix of the behaviours, emotions and body changes.
Tracy Gardiner, clinical director of CAMHS said the service - which provides an outreach service with consultations, training, joint-working, family group therapy and groups for young people - has seen an "increase in referrals" since it was strengthened by Welsh Government funding.
"It is important that we continue to work closely with our partners to deliver information and support for young people and their families," she added.
Eating disorder charity Beat said the risk is highest for young men and women between 13 and 17.
A spokeswoman said: "The fact that we are seeing parents and families spotting signs of an eating disorder early is positive. Full recovery from an eating disorder is possible but the sooner someone gets the treatment they need, the more likely they are to make a full and sustained recovery."
"Stereotypically, eating disorders are seen as a 'female disease' and we work hard to discourage this misunderstanding," the spokeswoman added, saying some research suggests the number of men accessing treatment had increased.
'Combination of factors'
In recent years, the Welsh Government has invested £1.25m in relevant services, including £1m to develop community adult treatment teams and £250,000 to improve children's services.
"There is often no known single cause and it is generally understood to develop as a result of a combination of factors, including the individual's genetic make-up, personality and biological factors, with possible triggers related to what is happening in the individual's life and social environment," a spokesman said.
What is important is services are in place to respond quickly to assess, diagnose and treat the condition, he added.
An extra £500,000 has been included in the 2017-18 budget to help foster closer working between children's and adult eating disorder teams.