A report by the association published on Tuesday identifies a link between the images of "abnormally thin" models which dominate TV and magazines, and the rise in conditions such as anorexia nervosa and bulimia.
It is the first time that the BMA has acknowledged such a link.
There are an estimated 60,000 people in Britain with eating disorders. Nine out of ten are female.
The report calls for urgent action to reduce the pressure on young women to be thin, asking publishers in particular to be more responsible.
The association asks for "more realistic body shapes" to be featured in a bid to cut the number of women dying from the so-called "slimming" diseases.
Schools are also encouraged to stamp out teasing of overweight pupils, and to encourage them to take part in sport.
Dr Vivienne Nathanson, BMA head of science, said: "The image of slim models in the media are a marked contrast to the body size and shape of most children and young women, who are becoming increasingly heavier."
Unrealistic role models
The report says that models and actresses in the 1990s commonly had body fat levels as low as 10% - the average for a healthy woman is 22% to 26%.
Dr Dee Dawson, from the Rhodes Farm Clinic, which treats sufferers, said: "We are seeing children as young as six, seven and eight-years-old who are worried about being fat and are exposed to pictures of thin models from a very early age."
Nicky Bryant, from the Eating Disorders Association, said several studies had shown that media portrayals of a thin ideal put pressure on youngsters.
She said: "We have noticed an alarming increase in the numbers of young people aged 13 years or under contacting our youth helpline with issues around eating."
Ms Bryant said eating disorders were linked to deep-rooted psychological disorders.
Under attack
Women's magazines have been under attack for years, accused of promoting unrealistic body images of exceptionally thin models.
Editor of Vogue, Alexandra Shulman, defended her publication's position in the light of the BMA findings.
"All we are doing is showing images of women we regard as interesting or beautiful or fashionable.
"But we are not actually saying you have to be like this."
Premier, the London-based model agency which represents supermodels Naomi Campbell and Claudia Schiffer, said women who bought fashion magazines featuring thin models were as much to blame as the editors and advertisers who used them.
"It is a supply and demand thing - advertisers, magazines and agencies supply the image that consumers want to see.
"Statistics have repeatedly shown that if you stick a beautiful skinny girl on the cover of a magazine you sell more copies."
Women's minister Tessa Jowell was so concerned about the problem that last month she held a summit meeting at Downing Street with the bosses of a top modelling agency and a teenage magazine.
The minister wanted to bring together influential people in the media and fashion worlds who could "begin to challenge some of the assumptions that the only way to be beautiful is to be thin".