The following is a transcript of a report by medical editor Marilyn Brooks that first aired April 7, 2008, on WTAE Channel 4 Action News at 5 p.m.

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The Food and Drug Administration demands that labels tell shoppers what's in packaged food products -- but it rarely tests those products.

Now, a laboratory test of a dozen of those products has found that the labels are not as accurate as you might think.

We hired a lab to do what the government rarely does -- test a dozen packaged food products.

"I don't think anyone knows for sure how accurate the nutrition labels are," said Delia Hammock, of the Good Housekeeping Institute.

Three product labels were off -- in a healthy way. Weight Watchers blueberry muffins contain even less fat than listed, while Nabisco Mini Oreos and Pepperidge Farm Chocolate Chunk cookies had more protein.

Basically, nutrition facts aren't so factual. The FDA allows foods to contain 20 percent more diet-damaging nutrients than listed before it takes enforcement action.

"If you're getting 20 percent more saturated fat or sodium in foods routinely, that's a major problem," said Michael Jacobson, of the Center for Science in the Public Interest.

All 12 products in the test were over for at least one nutrient.

Three were over by more than 20 percent:

David's sunflower Seeds -- 23 percent more saturated fat

Ritz crackers -- 36 percent more sodium

Wonder bread -- 70 percent more total fat

Here's another classic case of government double-speak. "No" means none, but "zero" doesn't always mean zilch. Manufacturers can list "0" even if a product contains up to a half-gram of a nutrient.

"So, to know these fine distinctions, you really have to read the rulebook," said Jacobson.

Despite "0" on the labels, small amounts of saturated fat were found in Baked Lay's potato chips, Rold Gold pretzels, Special K cereal and Grape Nuts trail mix crunch.

Nabisco Cheese Nips boast zero trans fat, but tests show each serving actually contains about a quarter of a gram of the artery-clogging fat. It's legal, but troubling, since the FDA says we should eliminate trans fat from our diets.

As for total fat, Snackwell's Devil's Food cookies list zero fat, but the lab found more than a quarter of a gram in each cookie. Again, it's legal.

Unfortunately, Americans very often eat two, three or four times the serving size. Six cookies equals a gram-and-a-half of fat.

The bottom line is, be skeptical of what you read on package labels. And if a food tastes too good to be true -- well, you know the rest.