A healthy diet includes ample portions of fruits and vegetables, but not the unhealthy dose of pesticides found in about one in five of the produce examined by Consumer Reports. 

An examination of 59 common fruits and vegetables found pesticides posed significant risks in 20% of them, from bell peppers, blueberries and green beans to potatoes and strawberries, according to findings published Thursday by the nonprofit consumer advocacy group. 

In its most comprehensive review yet, CR said it analyzed seven years of data from the Department of Agriculture, which every year tests a selection of conventional and organic produce grown in or imported to the U.S. for pesticide residues. 

"Our new results continue to raise red flags," CR said in its report. In addition to finding unhealthy levels of chemicals used by farmers to control bugs, fungi and weeds, one food — green beans — had residues of a pesticide that hasn't been allowed for use on vegetables in the U.S. for more than a decade. 

Imported produce, especially from Mexico, was particularly likely to carry risky levels of pesticide residues, CR found. 

The good news? There's no need to worry about pesticides in almost two-thirds of produce, including nearly all of the organic fruits and vegetables examined. 

The analysis found broccoli to be a safe bet, for instance, not because the vegetable did not contain pesticide residues but because higher-risk chemicals were at low levels and on only a few samples. 

Health problems arise from long-term exposure to pesticides, or if the exposure occurs during pregnancy or in early childhood, according to James Rogers, a microbiologist who oversees food safety at CR.

CR advises that shoppers limit exposure to harmful pesticides by using its analysis to help determine, for instance, when buying organic makes the most sense, given that it's often a substantially more expensive option.

The findings do not mean people need to cut out higher-risk foods from their diets completely, as eating them every now and again is fine, said Rogers. He advised swapping out white potatoes for sweet ones, or eating snap peas instead of green beans, as healthy choices, "so you're not eating those riskier foods every time."

"The best choice is to eat organic for the very high-risk items," Rogers told CBS MoneyWatch, citing blueberries as an example where paying more translates into less pesticides. "We recommend the USDA organic label because it's better regulated" versus organic imports, he added.

Thousands of workers become ill from pesticide poisonings each year, and studies have linked on-the-job use of a variety of pesticides with a higher risk of health problems including Parkinson's disease, breast cancer and diabetes. 

Kate Gibson

Kate Gibson is a reporter for CBS MoneyWatch in New York.