It's not just the fatty batter you need to worry about; it's the phosphate in the chicken, too.

Sodium, trans fats, hidden calories, genetically modified ingredients: Those are all good reasons to give up processed junk. And if you need one—or 45—more, there are phosphates, food additives that doctors are linking to higher rates of chronic kidney disease, weak bones, and premature death.

Listed under names like "sodium phosphate," "calcium phosphate" and "phosphoric acid," there are 45 different phosphate-containing food additives used in hundreds of processed foods, and unless you're a dedicated ingredient-list reader, you'd have no idea they're there. Food companies aren't required to list phosphate levels on the "Nutrition Facts" panel on packaged foods—they're not even required to analyze foods for phosphate levels at all.

And that's a real problem, says Janeen Leon, MS, RD, LD, a researcher at the Center for Reducing Health Disparities at MetroHealth Medical Center in Cleveland, who has spent much of her recent career researching phosphate food additives. "We're finding that, even among healthy adults, people with phosphate levels at the higher end of what's considered normal have higher mortality rates," she says. What's more, rates of chronic kidney disease, a slow loss of kidney function that requires dialysis treatments, or even organ transplants, have been on the rise, increasing 16 percent since the 1980s. "The rising rates of hypertension and diabetes likely play a role," she says, but physicians are starting to focus more of their attention on diet. "Though there's no hard evidence that high-phosphate diets cause kidney disease, there is sufficient data showing that phosphorous does cause a more rapid progression of the disease," she says.

In addition to chronic kidney disease and increased mortality rates, phosphate additives have been linked to an increased risk of heart disease, they're thought to accelerate the aging process, and they interfere with the way your body activates vitamin D. Too much phosphorous can also lead to weakened bones. In much of the professional research on heart disease, Leon says, "Doctors are making comments like, Is this the next trans fat? Is this the next cholesterol?"

Leon's concerns were echoed in a recent issue of the European medical journal, Deutsches Ärzteblatt International. In a paper analyzing the available literature on phosphate food additives and human health, the authors concluded that government officials need to institute stronger labeling laws for phosphate content in processed foods, and that food companies should be required to limit the amount of phosphates they add to products.

Where It's Hiding
Our bodies need phosphorous to survive; it's used to build and maintain strong bones and teeth, and cells use it to transport waste out of our systems. But the naturally occurring phosphorous found in whole grains, non-processed meats, poultry, fish, eggs, dairy products, nuts, and legumes is organic phosphorous. Our bodies only absorb 40 to 60 percent of that.

However, Leon says, the forms of phosphate added to foods are inorganic. They aren't chemically bound to fats and carbohydrates the way naturally occurring phosphorous is, and are much more easily absorbed by the body, leading to excessive levels of phosphate in the blood.

The recommended daily allowance for either form of phosphorous is 700 milligrams (mg) per day, yet most of us unknowingly eat about 1,500 mg. A few years ago, Leon did her own analysis of processed foods to determine which had the highest levels, and here are the sources that concern her the most:

• Frozen Dinners, which she says have varying levels of phosphorous all of which are "extremely high."

• Baked Goods. The baking powder used in muffins, cakes, and other processed baked goods is very phosphate rich. According to the European paper, a 14-mg packet (about 0.5 ounces) contains 1,500 mg of phosphorous.

• Processed Meats. The sodium phosphate added to sausage, lunchmeat, ham, canned fish, and other processed meats is used to keep them moist and tender during storage, and the levels can range from 50 mg to as much as 400 mg per serving.

• "Enhanced" Meats. The next time you're tempted to buy a "self-basting" turkey or other poultry advertised as containing "added broth," put it down. That broth, added to help the meat retain moisture during the cooking process, is mostly sodium phosphate, which can exist in the meat at levels as high as 400 mg, a nearly 30 percent increase in the amount of phosphorous that exists naturally in the meat.

• Convenience foods. "Kraft Macaroni and Cheese, flavored noodle mixes—those types of foods were very high in phosphorous," says Leon.

• Sodas. Sodas and fruit juice contain about 100 mg of phosphorous per serving but those levels "pale in comparison" to other foods, Leon says.

• Fast food and restaurant foods in general. Leon did a separate study on restaurant foods and found that a single chicken-and-fried-rice dinner at one Chinese-food chain contained 900 mg of phosphorous. "A lot of that has to do with the enhanced meats," she says. "It's getting difficult to get chicken that's not enhanced at the commercial level."

• Calcium-fortified foods. Leon is reluctant to condemn all calcium-fortified foods, but she says many are fortified with calcium phosphate, which can cause the fortified version to contain two to three times the phosphorous of its non-fortified equivalent.

Her final advice? We all need to eat less phosphorous, and the best way to avoid it is to read labels. "Read your labels for any words containing 'phos-,' and limit your fast-food consumption," she says.