WASHINGTON (AP) -- Food makers are jockeying for grocery shelf space in the low-carb craze, touting everything from salad dressing to ice cream to low-carbohydrate Easter chocolate.

Here's the catch: How companies count carbohydrates varies widely. While some significantly cut carbohydrates, others promoted as reduced-carb actually cut only a single gram per serving -- yet cost more -- and some simply leave ingredients out of their count.

Now the Food and Drug Administration is about to determine just how many carbohydrates are allowed for a food to advertise itself as low- or reduced-carb, and exactly how manufacturers should count the grams.

It's an effort to "demystify the current confusion about carbohydrates," says FDA Deputy Commissioner Lester Crawford, who expects a substantial number of products will have to change their labels as a result.

As the FDA deliberates, nutritionists advise consumers to get savvy: Just because a product touts itself as low or reduced in carbohydrates doesn't necessarily mean it fits your diet.

Remember the low-fat craze of the early '90s, when cookies and other goodies were revised to contain fewer grams of fat? Low fat didn't always mean low calorie, and many people who swarmed back to foods they'd long avoided regained pounds.

"We're almost seeing the same trend," says Dr. Alice Lichtenstein, a nutrition specialist at Tufts University. With low-carb diets, "it used to be you couldn't eat pasta or crunchy snacks, all sorts of things. Now suddenly there are low-carb versions of anything. ... I suspect what we're going to see is that the low-carb diets are not going to be as successful as previously."

Low-carb doesn't equal low calorie count
Indeed, a consumer advocacy group recently counted calories on some restaurant chains' low-carb menus, with some surprising results. Consider Ruby Tuesday's low-carb steak or fajita entrees, with about 1,000 calories, says the Center for Science in the Public Interest. Or Subway's low-carb wraps, which had more than 100 extra calories over the chain's famed line of low-fat subs.

There were some trimmer options. At Subway, ask for a low-fat sub to be wrapped in a lower-carb tortilla instead of a bun, CSPI advises. Ruby Tuesday's low-carb fish or grilled chicken were also low in calories, CSPI found, and the restaurant's new policy of listing calories on the menu should help consumers decide.

Grocery shelves may be even more confusing, says CSPI nutritionist Bonnie Liebman, who complains that "this carb craze has been going on for months now and FDA has been silent."

She points to low-carb ice cream that actually has as much fat and calories as regular, calling the fat-free version a better treat for most dieters. Zero-carb salad dressing sits next to the cheaper regular version with its 1 gram of carbs.

Then there are products that list total carbohydrates on the package back as the law requires -- but different "net carbs" on the front.

What are net carbs? Partly, it means carbohydrates minus insoluble fiber. Some breads, for instance, cut carbohydrates by increasing fiber content, a change even low-carb critics praise because most Americans don't eat enough fiber.

Labels debated
Some companies also replace sugar with sugar alcohol maltitol and then don't count the maltitol, arguing it shouldn't count because it has little impact on blood sugar levels. In a handful of warning letters accusing companies of misleading carb claims, FDA has insisted maltitol is indeed a carbohydrate. (Too much also can cause diarrhea and other gastrointestinal distress in some people.)

"Low carb" or "reduced carb" aren't allowed on food labels until FDA defines those terms, and the agency has ordered a few companies to quit using them. The maker of Nature's Own Wheat 'n Fiber bread changed its name from the original "reduced carbohydrate" last year just before receiving FDA's order; Pure De-Lite quit calling its dark chocolate bar "low-carb."

Now the Grocery Manufacturers of America, the trade group representing most major brands, has petitioned FDA to define low-carb as 9 grams of carbohydrates per 100 grams of food, a typical serving.

It's not endorsing any particular weight-loss plan, but putting carbs on a level playing field with fat and other ingredients, says GMA nutrition director Alison Kretser.

The consumer advocacy CSPI wants low-carb defined as 6 grams per serving, and for "reduced carb" foods to have at least 25 percent fewer carbohydrates than original versions.

Stay tuned: FDA may decide by summer.