Washington ? 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 total 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,” said FDA Deputy Commissioner Lester Crawford, who expects a substantial number of products will have to change their labels as a result.

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.

Some companies also replace sugar with the 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, said the group’s nutrition director Alison Kretser.

Stay tuned: FDA may decide by summer.