Cashing in on the low-carb craze.

Old conventional wisdom: Low-carb dieters can't eat bread, pasta, cakes, cookies, candy, or other sweets.

New conventional wisdom: Low-carb dieters can eat almost any food, as long as they buy higher-priced, low-carbohydrate versions.

Well, not exactly low-carb. The supermarket shelves are exploding with "carb smart," "carb aware," and "carb sense" foods designed for "low-carb lifestyles." Here's a guide to help you wade through the flood of new foods carrying claims about carbohydrates.

* Low-carb claims are illegal. The Food and Drug Administration prohibits any nutrient claim that it hasn't defined. To their credit, some companies are waiting for the FDA to define "low-carb," just as it has defined "low-fat" and "low-calorie." But others are interpreting the rule to mean that only "low-carb" claims are banned.

Clearly, a claim like "carb countdown" or "carb fit" implies that the food has fewer carbohydrates than its counterparts. But most labels don't bother to back up the claim by comparing the new item to those counterparts (as the FDA requires for a "reduced-fat" or "reduced-calorie" claim). And in some cases, "lower-carb" foods don't have fewer carbohydrates ... they just have fewer "net carbs."

* Net carbs are unclear. Manufacturers get "net carbs" by subtracting sugar alcohols, fiber, and other carbohydrates that supposedly have "minimal impact on blood sugar." Is a carb that doesn't raise blood sugar no longer a carb? Should a company have to test a food to make sure that it doesn't boost blood sugar? What if companies started deducting fats that don't raise blood cholesterol to get "net fats" or sodium salts that don't raise blood pressure to get "net sodium"? The Nutrition Facts panel would become a zoo of competing numbers that would confuse and, in some cases, mislead the public.

* "Minimal impact on your blood sugar" doesn't mean minimal impact on your hips. The low-carb industry assumes that if your net carbs are low, your weight will follow. But the science just…