Phthalates come from a class of industrial chemicals that are used to make food packaging materials and other items involved in the manufacture of fast food and dairy produce.

Previous studies have suggested that these chemicals leach out of plastic food packaging, causing contamination of highly processed foods.

Researchers at Milken Institute School of Public Health at the George Washington University in Washington, DC, led by Ami Zota, are among the first to investigate the relationship between fast-food consumption and exposure to the chemicals.

Zota and coauthors examined data for 8,877 participants. To gather the information, they distributed a questionnaire and collected a urinary sample for each respondent.

The subjects answered detailed questions on what food they had eaten, including fast food, in the last 24 hours.

The researchers tested the urinary samples to see if they contained the breakdown products of two phthalates: di-isononyl phthalate (DiNP) and di-2-ethylhexylphlatate (DEHP).

23.8% more DEHP, 40% more DiNP in fast-food consumers
Findings showed that the more fast food an individual reported eating, the higher their exposure to phthalates.

Compared with those who had not consumed fast food, the urine of participants who ate the most fast food had 23.8% higher levels of the breakdown product for DEHP, and the levels of DiNP metabolites were 40% higher.

Meat items and grain-based foods, such as bread, cake, pizza, burritos, rice dishes and noodles, appeared to contribute the most significantly to phthalate exposure, supporting previous findings that grains are an important source of phthalate exposure.

Another chemical used in plastic food packaging, Bisphenol A (BPA), has been linked with health and behavioral problems, especially among young children. Zota's team also looked for signs of BPA among their participants.

High BPA levels after eating fast-food meat products
The team found no association between total fast-food intake and BPA, but those who consumed fast-food meat products had higher BPA levels than those who had not eaten fast food.

Ongoing research suggests that phthalates feature in a range of personal products, toys, perfume and even foods. In 2008, Congress banned phthalates in children's toys due to concerns that they could be hazardous to health.

There is also evidence that DEHP and DiNP leach out of products and into the body, potentially causing problems for the reproductive system, including infertility.

However, they remain in use, and it could be years before large studies confirm a link between phthalates, fast food and health problems, says Zota.

Meanwhile, she suggests avoiding frequent consumption of fast foods because of the amounts of fat, salt and calories that they contain.

She says people "can't go wrong by eating more fruits and vegetables and less fast food." She adds that the health benefits of consuming whole foods "go far beyond the question of phthalates."