Over the past decade, convenience stores have beefed up their focus on fresh and prepared foods with grab-and-go food service around the clock.

But depending on where you go and what you buy, some of that food may not be as fresh as you think, according to the findings of our investigation.

When Daniel Lutz of contacted the Problem Solvers in June, he already had worries. He was pressed to find a mode of transportation and a place to live, all with a baby on the way.

In the middle of all that, Lutz says his pregnant fiance got sick from an expired convenience store dairy drink.

We went to the store and she grabbed a fruit smoothie out of the shelf." Lutz explained.

Half an hour after drinking the bottled smoothie, Lutz says his fiance got violently ill.

"And so I grabbed the bottle from her. I said, 'What's the expiration date? ' And it said a month previous; it had expired."

Lutz says the date on the bottle was April 29. The purchase date? The second of June!

"So it was over a month expired on the shelf," said Lutz.

His fiance and unborn baby are OK, but the Problem Solvers wanted to see whether this was just an isolated case.

To find out, we went undercover to different convenience stores, including gas station mini-marts and mom-and-pop stores.

We checked dates on dairy products, fresh sandwiches and other perishables, including the dates on frozen packaged foods.

The dates can be confusing:

* "Sell by" tells the store not to sell the product after that date.
* "Use by" means don't use after the date.
* "Best by" is the manufacturer's recommended cutoff date for best quality. After that date, flavor, texture and appeal likely go downhill.

If there's only a date and no wording, that date generally refers to the "best by" deadline, according to food producers.

We purchased a carton of eggs on June 23. The date on the carton was June 15. That's eight extra days on the shelf.

A carton of yogurt purchased the same way was on the shelf nine days passed the sell-by date.

We purchased a bottle of orange juice that was three and a half weeks past the date. We also found chocolate parfait that was five weeks past the date.

One carton of cottage cheese purchased June 23 had a "best by" date of May 9 -- nearly six and a half weeks beyond the date the manufacturer recommends consuming the product.

During random checks over the summer and fall, we found old food with expired dates overlooked by consumers and store clerks.

A "fresh" bologna and cheese sandwich purchased purchased at a 7-Eleven store on Sept.4 had a best-by date of August 22.

But when I contacted county, state and federal health officials, there was very little concern. We were surprised to learn that in most cases, health inspectors don't even check.

"That's not typically something we're looking for, no," said Mark Rowe, manger of the Food Protection program for Public Health Seattle & King County. "From a regulatory perspective, the big issue with products that are past pull date and continuing to be sold, is one of wholesomeness, and the product being what we consider wholesome -- no foul odor, no discoloration, or leaking."

Health regulators repeatedly emphasized that with few exceptions, the package dating is a convenience for consumers so they have information about product quality; the dates are not about safety.

We purchased a bottle of orange juice on Nov. 3 that was dated Sept.25. Although the discolored juice was being sold more than a month past the recommended date for best quality, technically it was still safe to drink.

We purchased a frozen burrito from the same store on August 2. The label clearly reads "sell by Feb. 1."

During our random checks, only once did a clerk point out that a date had expired, and that was after we'd notified the corporate headquarters about what we'd found.

Subsequent visits to that particular chain did show a noticeable improvement. At one store that stood out for repeatedly having more expired products than others, our last visit only produced one expired product -- a "fresh" sandwich with a best-by date that was nine days prior.

The store clerk immediately took it to the back room when I pointed out the oversight.

"But there's also an onus on the purchaser - that once they purchase that product, that they know it's past the pull date," said Rowe.

Translation: Buyer beware.

Of the 13 convenience stores we checked - some of them on repeated visits, six were 7-Eleven franchises.While 7-Eleven were not the only stores selling food past the date, they did have the most instances of out-of-code products. Corporate executives and local managers were not happy to learn of what we had found.

After we alerted them in October, 7-Eleven says it started contacting every franchise in the state, which likely explains why we found improvement on subsequent visits.

This week, 7-Eleven's Corporate spokesperson Margaret Chabris e-mailed a response to our investigation which said, in part:

"When we first learned of this situation in early October, our field team immediately contacted all of the stores in Washington state to discuss this matter." (Read the full statement here.)

As a result of our findings, the 7-Eleven Corporation says it has ordered an aggressive inspection and enforcement plan to ensure no more out-of code products are available to consumers.

Other chains and independently-owned convenience stores we contacted did not return our calls.

Health officials, meantime, say at the very least, stores should isolate past-date products and make it clear to customers that the products they're buying have exceeded the manufacturer's best-by recommendation since some food are still perfectly fine.

Health officials add that if you do get sick from consuming what turns out to be expired food, save the package and what's left of the product and contact your local health department. In addition, you should always report situation where the date information has been altered.

To view a list of some of the past-date products we found during our random inspections, click here.