During recent Web chats, two Lean Plate Club members reported scrutinizing the nutrition labels of what they considered to be healthful foods only to discover an undesirable ingredient: partially hydrogenated oils.

"Isn't that trans fat?" asked a member from Rockwall, Tex.

In fact, it is.

"Does that mean we should avoid it?" asked a member from Fairfax who found the same ingredient in her canola-based margarine. "I usually go without a butter substitute on toast or in sandwiches, but my husband and two young children can't live without it, and I want to find something healthy for them."

And there's the rub for consumers trying to eat smart. Food manufacturers are not required to divulge how much trans fat, considered as bad as if not worse than saturated fat, is in their products. In 1999 the Food and Drug Administration proposed a rule to list trans fats on labels. Updated in November in the Federal Register, that proposal is due to be finalized this year; if that schedule holds, the rule could take effect next year.

In the meantime, "there's just no good rule of thumb for consumers to tell exactly how much trans fat is in their food," said Margo Wootan, nutrition policy director at the Center for Science in the Public Interest (CSPI), the District-based consumer group that has been leading the charge against trans fatty acids.

Found naturally in dairy products and meats, trans fatty acids are also produced during the processing that improves the stability and lengthens the shelf life of vegetable and fish oils. Among the leading food sources of trans fat are margarine, salad dressings and baked goods such as crackers, pastries and cookies.

Numerous studies suggest that trans fats raise heart disease risk by boosting levels of blood cholesterol -- particularly the most deleterious cholesterol, low density lipoprotein (LDL). That also can lead to undesirable ratios of "good" vs. "bad" cholesterol in the blood. In issuing the latest nutritional recommendations last year, the National Academy of Sciences suggested that trans fat intake should be as low as possible and concluded that "there are no data available to indicate a health benefit from consuming trans fatty acids."

Okay, so how come partially hydrogenated fat still winds up in supposedly healthy margarine or even low-fat salad dressing? "That's because there are trace amounts of trans fat in canola and soybean oils," Wootan says. "When the oils are deodorized and processed, trace amounts are created. But these are trivial amounts. Trans fat is not a poison. People shouldn't be trying to avoid every milligram, but they should try to limit their intake, just as they try to limit their intake of saturated fat."

Current recommendations are to limit saturated fat intake (including trans fats) to 10 percent or less of daily calories. The numbers work out to about "20 grams a day for people on a 2,000-calorie-a-day diet," said Wootan, whose organization is pushing for a footnote on food labels that would clearly show the amount of trans fat in foods. (For more information, log on to www.cspinet.org.)

Until then, here's what experts recommend to help minimize consumption of trans fats.

Reach for healthy fats whenever possible. Two good options for cooking and salad dressings are canola oil and olive oil, according to the American Heart Association's Nutrition Committee (www.americanheart.org/presenter.jhtml?identifier=4776)

Choose low-fat foods. Among the other foods high in trans fats are french fries and breaded frozen fish sticks. Products that have three grams or less of fat per serving "probably will be pretty safe," Wootan says. "In that case, they probably won't have more than a gram of trans fat."

Pick a tub margarine over stick. And then look for one that has "no more than two grams of saturated fat per tablespoon and with liquid vegetable oil as the first ingredient," according to the AHA nutrition committee. Some products also now note on their labels that they are free of trans fats .

THE MAKE THE MOVE CHALLENGE

* The goal this week is to try for four two-minute walks a day. Some ways to fit in extra activity: Pick up lunch a block or two from your office instead of at the in-house cafeteria; deliver a message in person instead of sending e-mail; make multiple trips to carry small loads of laundry or groceries. (For those new to Make the Move, it's an eight-week challenge launched earlier this month by the Lean Plate Club that is designed to slowly boost lifestyle activities for sedentary people as well as for those who work out regularly but may not be active much of the rest of the day. For more information, log on to www.washingtonpost.com/leanplateclub).

* Make a list of your most common obstacles to achieving daily activity, then make a companion list of possible ways around these obstacles. Lack of time is one of the chief barriers cited by people who don't get regular physical activity. But as experts note, everyone has the same 24 hours every day. Use your personal study guide from Week One (available at www.washingtonpost.com/leanplateclub) to spot opportunities for two-minute walks. Then use a daily calendar to schedule two-minute walks every day. And if it helps, find a walking partner to go with you.

-- Sally Squires

Trans, partially hydrogenated, saturated, mono-unsaturated and polyunsaturated fats: How do you make sense of them all? Tell us today, or ask any nutrition question, when Sally Squires hosts the Lean Plate Club, our online chat about healthy eating and exercise. You can join live from 1 to p.m. today at www.washingtonpost.com. To subscribe to the free, electronic Lean Plate Club newsletter, log on to: www.washingtonpost.com/wp-srv/email/front.htm