One trip to the grocery store and it's easy to find products that say zero trans fats.

But even with zero on the bag or the box, you'll find ingredients like partially hydrogenated soybean oil that have trans fats.

"The worst types of fat are trans fats," said Chrissy Barth, a registered dietician.

She tells her clients to read the ingredients, not just the labels.

"I think anything artificial, especially in large quantities, is poison to our bodies," Barth said.

So why does zero not mean zero? There are a few loopholes.

While the federal Food and Drug Administration demanded trans fats be listed, there are three rules that allow manufacturers to hide them.

• Food makers can round down measurements by .5 increments.
• The FDA allows their measurements on a nutrition label to be off by 20 percent. For example, if there are .6 grams of trans fat per serving, food makers can say it is .48 (which is 20 percent less) and still be in compliance.
• If the total is less than .5, they are allowed to write "zero."

Experts say that's not good for you. Trans fats provide a double whammy. It raises bad cholesterol and lowers good cholesterol.

Trans fats are also a known cause of heart disease. And now, a new study links them to colon cancer.

Studies show that just five grams of trans fat a day could increase your risk of heart disease by 25 percent.

"It's easy to consume that five grams per day of trans fat," said Barth.

The small percentages can add up fast...so what can you do?

Stop searching for zero in your grocery aisle. Instead, if you find the phrase "partially hydrogenated oil," put it down. Not buying it is the only way to keep your diet trans fat free.

Eighteen companies were contacted for this story and were asked to comment. Only seven of them did. Five said they are in compliance with FDA guidelines and two said it's only in their seasoning and still falls under the guidelines.

One important point, new research shows that natural trans fats in meat and dairy may be good for you.

Find out more about trans fats on the FDA’s Web site.

A congressman from New York has sponsored a Bill called The Trans Fat Truth In Labeling Act of 2009.

If it's passed, there will be no more loopholes and manufacturers would have to be precise with numbers.

They would be given 18 months to change their labels or simply get rid of the trans fats.

Responses from manufacturers in compliance with FDA regulations

Foster Farms

We have made strides in reducing the trans fat content of many of our frozen products and our labeling complies with USDA guidelines.

Unilever

Unilever has been a global leader in the production and innovation of the margarine/spreads category for more than 50 years, starting with the creation of the category as a healthier alternative to higher saturated fat-containing products like lard and butter. Over many decades, we have continuously innovated to make our products lower in saturated fat and higher in essential fats to optimize their nutritional benefits. In fact, we were on the forefront more than 10 years ago in voluntarily reducing trans fats from our food products.

We are clear and transparent about the nutritional profile of our soft spreads brands as they contain 0 grams trans fat per serving and are among the lowest in saturated fat in the market. This profile aligns with recommendations from leading health authorities, including the World Health Organization, American Heart Association, and American Dietetic Association to limit both trans and saturated fat intakes.

That said, we recognize that some consumers are concerned that partially hydrogenated fats are listed in the ingredient deck. Labeling guidelines issued by the U.S. Food & Drug Administration provide that if a product contains less than .5 grams (4.999) trans fat per serving it could be labeled 0 grams trans fat in the nutrition facts panel due to the current round-down criteria for quantitative disclosures.

Land O’Lakes

At Land O'Lakes we strive to provide meaningful information on the labels of all our products, while complying with all applicable state and federal regulations. Our goal is to enable consumers to make well-informed product choices.

We believe the most meaningful way to present product information is on a "per serving" basis -- because that's how most consumers make decisions about which products to buy and how much of a product to consume. The Food and Drug Administration (FDA) requires "per serving" information on product labels, and we support this requirement because it benefits consumers by helping them evaluate food products.

The principal display panel of our Fresh Buttery Taste® Spread indicates that the product contains 0 grams Trans Fat per serving. This statement is in full compliance with FDA guidelines. The inclusion of partially hydrogenated oil in the ingredient statement also complies with FDA labeling regulations.

We have reformulated Fresh Buttery Taste® Spread in the last five years -- enhancing the taste and reducing the amount of trans fat per serving. We're happy to provide this great-tasting product to consumers with a reduced level of trans fat per serving.

We have not re-sized portions per serving. Re-sizing portions is not an option, since manufacturers do not determine serving size. The FDA establishes the serving size for all products, and Fresh Buttery Taste® Spread has consistently and accurately identified its serving size as one tablespoon.

Valley Lahvosh

Not at all, as you noted, we are following FDA regulations regarding labeling requirements. We are not trying to mislead our consumers. The partially hydrogenated vegetable oil is clearly listed on the ingredient statement. The amount of partially hydrogenated vegetable oil in our product is so minimal that it calculates out to zero grams when analyzed by a lab. This is the reason we can make the zero grams trans fat claim.

We have re-formulated our product to remove the partially hydrogenated vegetable oil completely. Although the amount of trans fat in our products was negligible, we understood the concern over trans fats and responded accordingly. We started this process late last year and will eventually convert our entire product line. Our product has an 18-month shelf life so there is obviously product in the marketplace that was produced and shipped before this change.

P&G

Pringles has not used hydrogenated oils as a frying oil for many years and the brand does not contain trans fat. A few of our seasoned varieties have an insignificant amount of partially hydrogenated fat as a minor ingredient in the topical seasoning on the crisps. In the interest of transparent labeling, this ingredient is listed in the ingredient statement.

While we had no need to change our formula due to trans fat, we have upgraded our Pringles recipe to lower the level of total fat while offering the consumer the same great taste with an improved texture and crispier crisp. Our labeled serving size in our canister offerings remains at 1 oz as it has for many years. We also offer portion control products such as single serve Snack Stacks and 100 calorie packs.

Kroger (Fry's)

We started introducing more trans fat free foods in our stores as a result of growing customer interest in these products. To this end, we have re-formulated many products in the past several years.

We believe it is important to give customers information so that they can make their own choices. That is why we print nutritional keys on our own products in addition to the other nutritional facts found on products that include ingredients, serving sizes, etc.

As you've noted, trans fat is a type of fat that is formed when vegetable oils are hydrogenated. Trace amounts of trans fat occur naturally in all vegetable oils.

On our packaging, we do say that certain products contain "0 Grams Trans Fat per serving." It's important to note "per serving" because there is a trace amount of trans fat in the oil used in those products (naturally-occurring) yet it is minimal and meets FDA guidelines.

Frito-Lay

Our snack chips don't have trans fats -- corn-based chips (Cheetos, Tostitos, Doritos) since 2003 and potato-based (Lay's, Ruffles) since 2005. To accomplish this, we shifted from hydrogenated soy oil to corn and/or sunflower oil.

The hydrogenated oil is in the seasoning which is added after cooking. Seasoning is less that 1-2% of the product and they're trace amounts.