Produce consumption is down the most among Hispanics, young adults, seniors, and women this year compared with 2010, the poll found.
The poll also found that the percentage of people who said they "ate healthy all day yesterday" fell from 68.2 percent to 66.2 percent — a drop that translates to 4.5 million fewer American adults eating healthythis May than last May.
The percentage who said they smoke rose from 20.2 percent to 20.8 percent, and the percentage who said they exercised for at least 30 minutes three times in the last week fell from 53.6 percent to 52.9 percent.
In fact, adults' health habits have been worse in each of the past three months compared with the same months in 2010, the poll found.
In particular, Hispanics and young people were by far the least likely to eat produce frequently in 2011, with less than half of each group getting the recommended amount of fruits and vegetables at least four days per week, the poll showed.
The month of May typically kicks off the four strongest months of the year in overall healthy behaviors for American adults, because seasonal opportunities present themselves and more Americans seek healthier choices, Gallup said.
The poll results are based on the responses given in interviews of about 1,000 adults each day.
It is possible that the decline in the healthy behaviors is partly a result of sharply increasing gas prices, which may drive some Americans to less expensive, less healthy options, Gallup said.