The blogs have drawn their share of negative, even vicious comments. But for overweight readers, the messages are empowering  and liberating.

“Girlfriend, let me tell you, I am finally coming to grips with myself,” one fan commented on Ms. Harding’s site. “I will always be fat. I accept that now.”

Harriet Brown, a 49-year-old blogger in Wisconsin and an occasional contributor to The New York Times, encourages readers to take her “I Love My Body Pledge” (at harrietbrown.com), in which they promise not to talk “trash” about “how fat my thighs or stomach” are, and not “call myself a fat pig.”

Fat Fu’s anonymous blog (fatfu.wordpress.com) has a ruthless deconstruction of recent research like the “fat friends” study, as well as one of the most comprehensive lists of links to the fatosphere, including online communities, fashions and health sites for fat people. The Big Fat Deal blog (bfdblog.com) suggests 10 ways to be a “body positivity activist,” including “Be yourself,” “Understand that a lot of people are hateful morons” and “Don’t be afraid to order the cheesecake.”

Many of the bloggers are women whose writing has a distinctly feminist flavor, but there are male fat-acceptance bloggers like Red No. 3 (red3.blogspot.com), who says: “See, I don’t have a problem with fat. My body is simply adorned, and I’ll take that.”

But some experts say this sort of message is dangerous and undermines public health efforts to rein in obesity. “We do have to be careful not to put all the blame on the individual,” said Dr. Walter C. Willett, professor of nutrition and epidemiology at the Harvard School of Public Health. But he added, “The large majority of people who are overweight are overweight because of lifestyle.”

The bloggers argue that changes in definitions over time, along with flaws in the body mass index formula, have pushed more Americans into the “fat” and “obese” categories, and they point to provocative studies suggesting that there may be benefits to being overweight, including a large study that found that underweight Americans are more likely to die than those who are moderately overweight.