Just weeks after the American Medical Association declared obesity to be a disease, one plaintiff has already filed suit in federal court claiming he was terminated because of his weight in violation of the Americans with Disabilities Act.

In June the AMA upgraded obesity from a condition to a disease. Defined as having a body mass index of 30 or higher, obesity is a "multimetabolic and hormonal disease state" that results in health conditions like cardiovascular disease and type 2 diabetes, the group said.

"The suggestion that obesity is not a disease but rather a consequence of a chosen lifestyle exemplified by overeating and/or inactivity is equivalent to suggesting that lung cancer is not a disease because it was brought about by individual choice to smoke cigarettes," according to the resolution passed by the AMA.

The designation provides employees with an argument that they are protected under the auspices of the ADA, with a lighter burden to establish discrimination. With the support of the AMA's definition behind a plaintiff's case, employers may struggle to argue that obesity is not a covered impairment.

And one plaintiff is ready to find out whether that argument will work. Joseph Whittaker sued America's Car-Mart, Inc., alleging that he was fired after seven years of employment because he is "severely obese." Despite his weight, Whittaker said he could perform the "essential elements" of his job. His employer, however, regarded him as being substantially limited in the major life activity of walking and fired him from his job as the general manager of a dealership, he claimed.

Although Whittaker's complaint doesn't cite to the AMA's updated definition, it states that he was "at all times relevant a qualified individual with a disability within the meaning of the ADA."

Whittaker's suit, filed in the Eastern District of Missouri, seeks compensatory and punitive damages, including payment for emotional and mental anguish.

To read the complaint in Whittaker v. America's Car-Mart, Inc., click here.

Why it matters: Although only one state (Michigan) and six cities currently prohibit discrimination based upon physical appearance or obesity, employers may want to brace themselves for an increase in obesity-related litigation. The AMA's new definition will likely spur more than just Whittaker's suit, given that an estimated one-third of American adults are classified as obese, according to the organization. How the courts will handle the issue remains to be seen.