Weight may not affect your mood much if you're carrying a few extra pounds, but Americans who are heavy enough to qualify as obese are more likely to be diagnosed with depression than their overweight or normal-weight counterparts, according to a new Gallup study based on poll data.

The study, which surveyed a random sample of 250,000 American adults via phone, also found that both obese and underweight people experienced higher levels of negative emotions like sadness and worry than normal-weight and overweight individuals.

Weight and emotion

Using the body mass index (BMI) scale, which is a measure of fatness based on weight and height, the pollsters estimate that 36.3 percent of Americans are overweight, while 26.7 percent are obese. Just over 35 percent are of normal weight.

Close to a quarter, or 23.2 percent, of obese Americans had been diagnosed with depression, compared with 14.3 percent of normal-weight Americans and 14.9 percent of those who are overweight, the poll found.

Just over 41 percent of obese Americans reported feeling stress the previous day, compared with 37.4 percent for the overweight and normal-weight groups.

Similarly, 34.5 percent of obese respondents had experienced worry the previous day, compared with 30.6 percent of normal-weight and 29.5 percent of overweight respondents. Obese respondents were also 2-3 percent more likely to experience anger than normal-weight and overweight Americans, and about 4 percent more likely to report sadness.

Underweight Americans, the smallest group at 1.7 percent of all respondents, felt similar levels of negative emotion as obese respondents, though they did not experience depression as often. Just over 19 percent of underweight Americans reported a depression diagnosis.

Which comes first, weight or depression?

The poll can't determine whether depression and negative moods contribute to making a person obese, or whether the extra weight causes people distress due to stigma or personal health problems. But previous studies have found that depression alone can cause weight gain.

Either way, Gallup reported, obesity rates have held around 25 percent since the company first started tracking Americans' weight in 2008, suggesting that associated mental health disorders could have a big impact on the population.

The Gallup-Healthways Well-Being Index was conducted between Jan. 1 and Sept. 14. The margin of error is plus-or-minus 1 percent.