"There are no federal laws on the books that make it illegal to discriminate on the basis of body weight, so on the whole it remains legal. That sends a message that it's no big deal," said Puhl.
Puhl suspects that public health campaigns branding obesity as a disease are sometimes perceived as criticizing individuals rather than the environmental and social factors that lead to weight gain. This, she said, gives some people license to engage in public fat-shaming.
She also believes media portrayals of heavy people as fat, lazy and gluttonous do them no favors.
"Overweight people are usually shown in stereotypical ways -- engaged in out of control eating or bingeing on junk food -- and they are often shown as the target of humor or ridicule," she pointed out. "With the amount of media we all consume, it's no wonder these stereotypes stick."
Big Changes Needed
Puhl said because of the public's belief that obesity is a temporary condition completely under an individual's control, fat people didn't get much sympathy, even from others struggling with their own weight.
"For things to change there needs to be a greater understanding of how complex the condition is and how hard it is to reverse," she said.
Even as obesity rates continue to soar, Puhl hasn't seen much improvement in public perception except for a few glimmers of hope in the workplace and health care environment.
Tiggeman, for one, is fighting back. She's suing Southwest, not for monetary gain but to force the airline industry to address its policies regarding overweight passengers, she said.
"I have no problem being held to a standard, but I think that standard shouldn't be applied arbitrarily based on how an airline employee feels about my size," she said. "We need to know if we need one seat or two, because this eyeballing happening at the gate is incredibly discriminatory, and it's so unnecessary."
Tweet chat: Why Are We Fat and What Can We Do About It?
To raise public awareness about obesity prevention and treatment, Dr. Richard Besser, ABC News' chief health and medical correspondent, will host a one-hour "tweet chat" on Twitter today from 1-2 p.m. ET. To participate, sign into Twitter and click here for the hashtag. Follow the conversation or jump in with comments and questions of your own.
Medical experts from the American Council on Exercise, the Academy of Nutrition and Dietetics, Center for Science in the Public Interest and Cornell University will join Besser on the chat to answer your questions and offer advice.