When Gatorade fan Sarah Kavanagh learned that her favorite drink contains an emulsifier banned in other countries over health concerns, she was taken aback.

"I was shocked that they'd put their consumers at risk like that and that the FDA would allow something like that to be put in products," said the Mississippi 15-year-old, who launched a petition in November asking Gatorade to remove the ingredient, called brominated vegetable oil, or BVO.

The petition, which has attracted more than 200,000 supporters on change.org, notes that the ingredient shares an element — bromine — with some flame retardants used in furniture and plastics. Some studies on BVO indicate it can build up in fatty tissues and cause reproductive and behavioral problems in rodents.

It's illegal to use the chemical as a food additive in the European Union India, Nepal, Canada, Brazil and Japan. Other ingredients that are allowed in American food but not in other countries include certain artificial colors and additives to flour.

Why the difference? The U.S. Food and Drug Administration would not provide a representative for an interview, but in past statements to the media and on its website the agency has presented a variety of reasons for allowing controversial chemicals in food, ranging from a lack of resources for research to assurances that the substances are safe in small doses.

In the case of BVO, the agency has allowed "interim" use of the ingredient since 1970, pending additional toxicological tests. Asked why it has not dealt with the interim status in more than 40 years, the agency cited a need to "maximize its resources" and said addressing the issue is "not a priority for the agency at this time."

"FDA's mission is first and foremost to protect public health by ensuring that foods are safe and properly labeled," the agency said in a statement, contending that science-based implementation of federal law has helped make the U.S. food supply "the safest in the world."

Unsatisfied with these kinds of answers, activists and public health watchdogs have urged the FDA and food makers to halt the use of various chemicals until safety can be fully determined. Food companies, they note, have reformulated their products for other countries — including members of the European Union, China, Australia, Japan and India — but seem reluctant to change their products in the U.S. until they must.

"There are all of these ... compounds on which the EU has taken action to the point that companies with global production have to have a separate line that's able to meet the EU standards and then a line for every place else, including the U.S.," said Michael Hansen, senior scientist at Consumers Union, a consumer advocacy group.

Michael Jacobson, executive director of the Center for Science in the Public Interest, has been lobbying the FDA for decades to reconsider its stance on ingredients from potassium bromate, a flour enhancer, to trans fats and some artificial colors. But all are still allowed.

"The FDA has been extremely lenient in evaluating food additives, and it's almost impossible to get the FDA to ban an additive once they have approved it," Jacobson said. "It's just not as public health-oriented as it should be."

Jacobson said it's unclear whether the inaction stems from industry pressure, fear of litigation or more pressing priorities, but the longtime activist believes that potentially harmful additives — even ones consumed by millions every day — are not being adequately vetted.

As an example, Jacobson said he and colleagues last year urged the FDA to re-examine aspartame, the sweetener used in most American diet drinks, in light of recent studies in Italy that suggested a link to cancer in rodents. After the agency "nitpicked" aspects of the research, Jacobson said, he asked FDA officials if they would at least call for further safety studies by the makers.

"FDA said simply 'no,'" Jacobson recalled. "And it was really frustrating. I just don't think they're doing enough to protect the public's health with regard to food additives."

Nutrition specialist Jayson Calton said many ingredients remain in American food simply because many consumers are unaware of the issues and don't complain.

"I think the companies figure let's leave well enough alone and not tell the consumer about what's going on, and as long as they're not asking questions, we'll do fine," said Calton, who outlines concerns over 13 common American food additives in his upcoming book "Rich Food Poor Food," written with his wife, Mira. "Most of these companies do business in the (United Kingdom) and the EU, and they are able to produce them just fine without the banned ingredients, but ... they don't do anything about them here."

The FDA is required to conduct premarket testing for some new food ingredients, but others simply need an OK from experts hired by the manufacturers. Those companies are not required to show the FDA their reasoning or even to notify the agency before using the ingredient. The agency can ask to see the research and investigate if health issues emerge later.

European authorities have relied more on the precautionary principle, which means erring on the side of caution when scientists have yet to reach firm conclusions on health risks of new products or those already on the market. Some observers credit the system with helping to protect consumers; others say the process can be unduly influenced by factors other than hard science.

Some European regulatory decisions based on the precautionary principle "go beyond scientific evidence … to consumer wishes and political considerations," said food scientist John Lupien, former chief of the food and nutrition division of the United Nations' Food and Agriculture Organization.

Hansen, the consumer scientist, said he believes the EU's process is scientifically rigorous — and consumers often have just cause for concern.

"In the U.S., money rules, and industry wields a lot of influence, and that's how it has been for a while," Hansen said, "but in Europe they take into serious consideration what their population wants too. And why shouldn't the population be concerned about new things being put into food?"