In an interview with the fashion Web site WWD, Moss said one of her mottos was "nothing tastes as good as skinny feels."
The same slogan is posted on Web sites encouraging girls not to eat.
Mary George of British eating-disorder charity Beat called Moss's words "very unfortunate."
"Comments like this make it even more difficult" for young people struggling with an eating disorder," she said.
Model Katie Green, who is campaigning to stop the use of ultra-thin "size zero" models, told The Sun newspaper the comments were "shocking and irresponsible."
Moss, 35, is famous for her waif-like look, which helped spur a trend for super-thin models in the 1990s.
Moss's modeling agency, Storm, said her words had been misinterpreted.
"This was part of a longer answer Kate gave during a wider-ranging interview, which has unfortunately been taken out of context and completely misrepresented," the agency said in a statement. "For the record, Kate does not support this as a lifestyle choice."
British clothing sizes are normally two sizes above clothing sold in the U.S., so a 'size zero' in the United States would be a size 4 in Britain.