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"I don't think anyone knows for sure how accurate the nutrition labels are," said Delia Hammock, Good Housekeeping Institute.
First the good news -- three product labels were off, but in a healthy way. Weight Watchers Blueberry Muffins contained even less fat than listed. Also, Nabisco Mini Oreos and Pepperidge Farm Chocolate Chunk Cookies had more protein.
They're called nutrition "facts," but they're not always so factual. The government actually allows foods to contain 20 percent more diet-damaging nutrients than the label lists before taking enforcement action.
"If you're getting 20 percent more saturated fat or sodium in foods routinely, that's a major problem," said Michael Jacobson, Center for Science in Public Interest.
All 12 products tested were over for at least one nutrient, and three were over by more than 20 percent: David's Sunflower Seeds with 23 percent more saturated fat; Ritz Crackers with 36 percent more sodium; and Wonder Bread with 70 percent more total fat.
In another classic case of government double-speak, "no" means none. But "zero" doesn't always mean zilch. Manufacturers are allowed to list "0" even if their product contains up to half a gram of a nutrient.
"So to know these fine distinctions, you really have to read the rule book," said Jacobson.
Despite the "0" on the labels, there were small amounts of saturated fat in Baked Lay's Potato Chips, Rold Gold Pretzels, Special K cereal and Grape Nuts Trail Mix Crunch.
The government says trans fats are downright dangerous. The Nabisco Cheese Nips label boasts 0 trans fat. But, according to the test, each serving actually contains about a quarter of a gram of the artery-clogging fat.
It's perfectly legal, but also troubling because the Food and Drug Administration says Americans should try to eliminate trans fat from their diets.
"That's right. You have to look for foods that say 'no trans fat.' Those can't have any trans fat," said Jacobson.
As for total fat, consider Snackwell's Devil's Food Cookies. With zero fat listed, they're supposed to be a guilt-free treat for dieters. But the lab found more than a quarter of a gram of fat in each one-cookie serving. Again, it's legal -- but who has just one?
"Unfortunately, Americans don't eat just the serving size on the label. Very often, maybe two, three, even four times as much," said Hammock.
Good Morning America emphasizes their study was small, and they only tested one sample of each product. When the FDA tests, it buys multiple samples from different lots.
Several of the food companies that were tested responded to the study. Interstate Bakeries, which makes Wonder Bread, called the research questionable, saying: "It is possible that a sample from one part of the loaf could have a slightly different fat content from another slice."
Kraft Foods, which makes Ritz Crackers, says: "The lot tested had undergone checks for compliance. There saw no deviation from production specifications."
And Conagra Foods says no two sunflower seeds are alike: "Weather, size of seeds, and other factors are dictated by Mother Nature and our labels reflect the average."