Around one in five sufferers of eating disorders are waiting more than a year for NHS treatment, according to a new report.
Over a third of patients are waiting more than six months, says charity Beat.
Eating disorders are estimated to cost the UK economy £8 billion.
The findings highlight inconsistent access to treatment as one of the factors to blame.
Statistics show that timing is crucial when treating eating disorders, which include anorexia, bulimia and binge eating.
Relapse rates for sufferers go down from 63% to 33% for those who sought early help.
Susan Ringwood, chief executive of Beat, said referrals within health services often take too long.
She said: “We need to see things changed, services need to be joined up. They’re fragmented and there’s too much wait and see.
“There are also too many artificial barriers and perverse incentives in the system. Those have got to come down.”
Kat Pugh, 25, has suffered with eating disorders since she was 11 years old.
She has had to resort to paying for private treatment after waiting more than a year on the NHS.
“What we should be looking at is intervening before it gets to this point,” she said.
“We shouldn’t be waiting until a person is requiring serious intervention. We should be helping them as soon as they recognise they have a problem.
“If you get help in the first three years of having an eating disorder the more likely you are to make a long term successful recovery.”
The Government announced a £150m investment to improve treatment last year.
Beat welcomes the pledge, but is also calling for the introduction of NHS waiting time targets for mental health.
The charity says eating disorders claim more lives than any other mental illness – one in five of the most seriously affected will die prematurely from the physical consequences or suicide.