Obese and overweight Americans combined for more than 60 percent of the population, said a recent Gallup poll, measuring overweight Americans with normal-weight Americans.

Although, the percentage of Americans of normal weight has slightly increased in the past year, but overweight and obese people still command a solid majority, according to a new study.

In the third quarter of 2011, 36.6 percent of Americans were of normal weight, compared with 35.6 percent a year ago, the Gallup-Healthways Well-Being Index survey found.

Although the majority of Americans are still overweight or obese, it is an encouraging sign that obesity rates are trending downward in the U.S., the study said.

The survey found 35.8 percent of Americans to be overweight, compared with 36.0 percent a year ago, and 25.8 percent obese, down from 26.6 percent last year.

Gallup researchers are not sure why weight levels saw a decrease, but they suggested a growing awareness of obesity-related health problems, rising healthcare costs, and health initiatives such as First Lady Michelle Obama's Let's Move! campaign.

Still, 61.6 percent of Americans are either overweight or obese, the study noted.

Researchers added that it was not clear what caused the change, but said it could be due to the tough economy, with cash-strapped Americans choosing to eat in rather than eating at high-calorie restaurants.

A downward trend in obesity rates could also mean a drop in U.S. healthcare costs, the study said.

The U.S. Centers for Disease Control and Prevention (CDC) estimated medical costs associated with obesity were $147 billion in 2008.

The study used self-reported data of height and weight to determine a score of body mass index. It was based on telephone interviews with a random sample of 90,070 people aged 18 and older from July to September, and had a margin of error of plus or minus one percent.