However, the Gallup-Healthways Well-Being Index found slight declines in the percentage of Americans who are classified as overweight and normal weight.
The percentage who were overweight fell to 35.6 percent so far this year from 36.1 percent in 2012, while the percentage who are a normal weight slipped to 35.4 percent from 35.9 percent in 2012.
Gallup and Healthways began tracking Americans' weight in 2008. The 2013 data are based on more than 84,000 interviews conducted Jan. 1 to June 20. Gallup uses respondents' self-reported height and weight to calculate body mass index scores. Individual BMI values of 30 or above are classified as obese, 25 to 29.9 are overweight, 18.5 to 24.9 are normal weight, and 18.4 or less are underweight.
The upward trend in obesity so far in 2013 reversed the lower levels found in 2011 and 2012. One possible reason was fewer Americans were exercising frequently in 2013 compared with 2012, Gallup said. In the past, Gallup found exercising three days per week for 30 minutes per day was closely linked to having a lower BMI.
The telephone survey was conducted Jan. 1-June 20 with a random sample of 84,463 adults. It has a margin of error of 1 percentage point.