Although the percentage of American adults who are overweight or obese keeps climbing, the percentage of Americans who are attempting to shed their excess pounds is dropping, a new analysis suggests.

Researchers found that over a 26-year period, the prevalence of adults in the United States who were overweight or obese rose from 53 percent in 1988 to 66 percent in 2014.

However, during this time frame, the prevalence of overweight individuals who reported that they had tried to lose weight in the past year fell from 56 percent in 1988 to 49 percent in 2014, according to the findings, published today (March 7) in the journal JAMA. [The Best Way to Lose Weight Safely]

These findings were not surprising, said the study's lead author, Dr. Jian Zhang, an associate professor of epidemiology at Georgia Southern University in Statesboro, Georgia.

As more and more people become overweight or obese, the body weight that is considered socially acceptable is also shifting toward the heavier side, Zhang told Live Science. In other words, Americans are getting used to seeing larger body sizes, and as a result, heavier people may be more satisfied with their weight and less motivated to lose it, he speculated.

More social acceptance

In the study, researchers analyzed data collected from the National Health and Nutrition Examination Survey, a federal survey done annually to evaluate the diet and health status of adults and children in the U.S. The researchers looked at information gathered during three time periods, all of which fell between 1988 and 2014, from about 27,000 adults ages 20 to 59 who were overweight or obese based on their body mass index (BMI).

All participants were asked whether they had attempted to lose weight in the past year.

The analysis revealed that black women represented one of the groups most affected by excess body weight. The prevalence of obesity among black women rose from 35 percent in the time period between 1988 and 1994, to 55 percent between 2009 and 2014, according to the findings.

Although 66 percent of black women who were overweight or obese reported that they had tried to lose weight between 1988 and 1994, only 55 percent said they were attempting to shed pounds between 2009 and 2014. [Weight Loss Drugs: Pros and Cons of 5 Approved Prescriptions]

The study also showed that white women seemed less interested in losing weight over time: 73 percent of white women who were overweight or obese said they tried to lose weight between 1988 and 1994, but 62 percent of them said the same between 2009 and 2014.

The percentage of U.S. adults who were overweight or obese increased in both women and men, and in all three of the major ethnic groups that the researchers looked at — whites, blacks and Mexican Hispanic Americans — over nearly three decades, the study found.

One limitation of the analysis is that it relied on self-reported data from the participants, rather than information from medical records. However, self-reported information can indicate emerging health trends within the population, and there has been other scientific evidence suggesting a shift in social norms about body weight in the U.S., the researchers said.

Even though the study did not look at why a smaller percentage of Americans may be trying to slim down, the researchers suggested some possible reasons.

It's hard to drop pounds, and many people who have repeatedly tried and failed may simply give up, Zhang said. In addition, health care providers may not bring up weight issues with their patients, the authors noted.

What can be done to reverse these obesity trends?

The best way to reduce rising rates of overweight and obesity is for people to prevent weight gain in the first place, Zhang said. More needs to be done to prevent obesity at its beginning — among kids, at home and in school, he suggested.

"That is the right-time, right-person and right-place strategy," Zhang said.

Originally published on Live Science.