(NBC NEWS) -- The American Medical Association officially designated obesity as adisease on Tuesday - a disease that requires medical treatment andprevention.

The organization doesn't have any kind of officialsay in the matter, but it's influential nonetheless, and the vote ofthe AMA's policy-making House of Delegates is one more step in theevolution of social attitudes towards obesity.

"Recognizingobesity as a disease will help change the way the medical communitytackles this complex issue that affects approximately one in threeAmericans," AMA board member Dr. Patrice Harris said in a statement.

Onethird of Americans are obese - and that's on top of the one-third whoare overweight. Obesity is more than just a matter of carrying aroundtoo much fat, says Dr. Michael Joyner, an exercise physiologist at theMayo Clinic in Rochester, Minn.

"The fat cells themselves wethought of for a long time as just warehouses for energy," Joyner saidin a telephone interview. But they also secrete chemicals, includingchemicals that can cause inflammation, raise blood pressure and thatdown the road help harden the arteries.

"More widespreadrecognition of obesity as a disease could result in greater investmentsby government and the private sector to develop and reimburse obesitytreatments," the AMA said in one statement on the issue.

"Employersmay be required to cover obesity treatments for their employees and maybe less able to discriminate on the basis of body weight."

The downside, the AMA says, is that people may expect that should be able to take a pill and "cure" obesity.

Thatclearly isn't going to happen, Joyner says. Pharmaceutical companieshave tried and tried, but just a very few drugs are approved for weightloss and even they don't produce spectacular results.

"It is very,very difficult, once people get fat, to lose fat and keep it off,"Joyner says. "We live in a low-physical-activity, high-calorie,high-food-variety environment," he added. "We are bombarded with imagesof food."

But designating obesity as a disease could make iteasier for policymakers to make changes. This has happened before withpublic health - once with smoking, and again with driving safety.

Withsmoking, first the U.S. Surgeon-General declared that smoking couldcause disease, then gradually workplaces and then public places beganbanning smoking. Taxes on tobacco and restrictions on who could buytobacco products helped - and smoking rates plummeted from above 40percent in the 1960s to 18 percent now.

With traffic safety, firstspeed laws, then requirements for vehicles to have seat belts and airbags helped reduce deaths, Joyner said.

Now something policy measures are needed for obesity, the AMA says.

"It changes the ways society looks at things. It gives people maybe a new set of tools," Joyner says.