Editor's note: This is the second of a two-part series on health claims on food labels.

According to an article published in a recent issue of the American Journal of Preventive Medicine, people don't really understand the nutritional information or health claims on food packaging labels very well. In fact, sometimes the claims themselves (even though they are within the context of the law) can lead us astray by giving foods an undeserved "health halo."

"The intention (of health claims on food packaging) was to help consumers differentiate which products have some health advantage," said Jeffrey Novick, director of nutrition at the Pritikin Longevity Center & Spa in Aventura, Fla. "Unfortunately, it didn't work and only made things more confusing. Even worse, the food industry took advantage of the loopholes in their marketing of their products."

Here are a few types of claims, what they mean and why they matter (or don't):

STRUCTURE/FUNCTION CLAIMS

What they mean: Manufacturers may make statements about the effects of a food substance (nutrient or dietary ingredient) on the structure or function of the body. For example, "Calcium builds strong bones." Unlike health claims, structure/function claims do not deal with disease risk reduction. The claims must be truthful and not misleading, but they are not pre-reviewed or authorized by the Food and Drug Administration.

Why they matter: These claims are intended to provide positive messages as a powerful means to promote a healthy diet and sell healthier foods. However, they are more confusing than helpful.

How can the claims be misleading or confusing? According to Novick, "Almost all the claims are worthless. They are misleading and give a false impression of the health value of the food."

How can you recognize structure/function claims on food labels? According to Luise Light, author of "What to Eat: The Ten Things You Really Need to Know to Eat Well and Be Healthy" (McGraw-Hill, 2006), you should look for a particular food substance, say a nutrient or dietary ingredient (e.g., calcium), and then look for terms such as: "strengthens memory," "relieves stress," "increases energy," "reduces frustration," "builds strong bodies," "improves sleep," "aids in weight-loss."

Example: "Good diets and exercise promote better health and prevent disease," "fiber maintains bowel regularity" or "antioxidants maintain cell integrity."

What's the most important, relevant structure function claim? None. "There is more to bones than just calcium and more to colon health than just fiber. These claims are of very little help to the consumer who wants to determine the value of the food or supplement to overall health," says Lona Sandon, a spokesperson for the American Dietetic Association.

NUTRIENT CONTENT CLAIMS

What they mean: Also known as "descriptors," these claims on food labels directly or by implication characterize the level of a nutrient in the food (such as "low fat" or "high in oat bran").

Why they matter: They give you a description that can help you make better, healthier choices.

How can the claims be misleading or confusing? A manufacturer could say that a cup of soup with 500 milligrams of sodium has "reduced sodium" just because it contains less sodium than a similar product or simply because the serving size is smaller. However, reduced sodium is not the same as low sodium, and 500 milligrams still may be too much for someone with high blood pressure. Consumers may think they are doing something good by using reduced/less versions of some foods but still be taking in too much of the nutrient in question for their health conditions, says Sandon.

How do you know it's a nutrient content claim on a food label? It will be a descriptive term relating to a nutrient (such as cholesterol, fat, sodium, calories), and it will include words such as "low," "reduced," "free," "less," "good source," etc. Examples: A "reduced calorie" food contains at least 25 percent less of some nutrient or calories than the original version.

What's the most important, relevant nutrient content claim? Healthy. To be labeled "healthy" a food must meet the definition of "low" for fat and saturated fat, and neither cholesterol nor sodium may be present at a level exceeding the levels set by the FDA.

DIETARY GUIDANCE STATEMENTS

What they mean: Typically, a dietary guidance statement makes reference to a category of food (fruits and vegetables) and not an individual nutrient or ingredient.

Why they matter: They're positive statements that help consumers to more easily identify healthy food categories.

How can the claim be misleading or confusing? It doesn't mean that the food is great overall, and it doesn't tell you how much or how often to eat the food for health benefits. There is no practical advice here, says Sandon.

How can you recognize a dietary guidance statement on a food label? It refers to a specific food or food component but not a disease or health-related condition, such as, "Carrots are good for your health," or "Calcium is good for you." The statement may make a specific disease claim, but it doesn't relate back to the specific product. It is not a health claim because it cannot reasonably be understood to be about a specific substance.

Example: "Diets rich in fruits and vegetables may reduce the risk of some types of cancer."

What's the most important, relevant dietary guidance statement? Connecting fruits and vegetables to a reduced risk of cancer.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.