Good for what ails you? Some foods claim to be

Cheddar that reduces cholesterol. Juice that aids flexibility. Salad dressing that protects against heart disease. Dinner these days is more than sustenance; it's also medicine.

There is no accepted definition for functional foods, also known as phoods - the ph comes from pharmaceutical. Generally, the term refers to products with added ingredients that enhance their nutritional profile and, in some cases, claim to fight illness.

One thing is certain, though: Functional foods are big business. Mass-market sales of functional foods grew by 30 percent between 2002 and 2006, according to a recent report from market-research publisher Packaged Facts. The report projects that the market will grow to $39 billion by 2011.

But for consumers, the increasing number of health messages in the supermarket can be confusing and, some nutritionists advise, downright deceiving.

Many nutritionists feel confident in the health claims of products with ingredients that carry FDA-regulated labels. (In order to have an authorized health claim, an ingredient must treat a disease, and its manufacturer must demonstrate significant scientific evidence through placebo-controlled trials. But beware: There are different levels of FDA rankings (see accompanying box).

Carrying the highest FDA seal of approval are the plant stanols in Benecol, a line of products that includes caramel-like chews and margarinelike spreads. Other stanol- and sterol-based products, such as Lifetime Cheddar and Nature Valley Healthy Heart granola bars, also carry these claims.

"When you see a claim approved by FDA - for example, a product with plant sterols or stanols, calcium or folic acid - you can be pretty certain there's some value to taking it," says David Schardt, senior nutritionist at the Center for Science in the Public Interest (CSPI).

The FDA also issues qualified health claims, which are given to functional ingredients whose evidence is still emerging. Among these is one of the most-hyped nutrients of the moment: the omega-3 fatty acids naturally found in fish. Recently, Tropicana introduced its Healthy Heart orange juice with omega-3 fatty acids from anchovies, sardines and tilapia. While there is no scientific consensus about the recommended daily amount of omega-3s in order to gain heart-health benefits, nutritionists agree that this is probably a good product.

"Orange juice with omega-3 fats could be a great thing for people if they don't like to eat fish," says Dave Grotto, a a registered dietician and spokesperson for the American Dietetic Association.

But Schardt warns consumers not to buy every product that carries an omega-3 label. Foods such as Quaker Take Heart oatmeal, Barilla pasta, and Promise Buttery Spread are fortified with a different, plant-based type of omega-3 fatty acid, alpha-linolenic acid (ALA), which has not been proven to have the same cardiovascular benefits as its fish-oil counterparts. These products carry no FDA health claim, but thanks to the good publicity surrounding fish-based omega-3s and consumer confusion, people may think they're getting the same heart benefits.

"It's deceptive for a product that has ALA to claim it will help lower risk of heart disease," says Schardt. "When consumers see omega-3 they automatically think of heart health, but there's a difference."

Most products that tout their healthful ingredients are not addressing diseases, and therefore are not evaluated by the FDA. Joint Juice, a beverage spiked with glucosamin, claims to help "joint health" by lubricating joints and maintaining cartilage, but the FDA has made no claim about the benefits of glucosamin. Schardt, for one, remains skeptical.

"The latest research by the federal government has found that glucosamin has no benefit for people with mild to moderate arthritis. It's not harmful to drink this product, but there's no proof that it will help."

Though Dannon's Activia yogurt, marketed with the suggestion that its added probiotics aid digestion and gut health, has been studied, the research is inconclusive.

"Several probiotic bacteria have been shown to help relieve diarrhea caused by antibiotics or irritable bowel syndrome, but there isn't good evidence that an ordinary healthy person benefits from taking these probiotics," says Schardt. Nevertheless, probiotics have been deemed one of the new frontiers for functional foods. They are now showing up in a host of new products, including a Kashi cereal called Vive.

Some functional foods may actually be harmful to consumers' health. One is CocoaVia, a chocolate bar fortified with plant sterol for cardiovascular health. The FDA wrote manufacturer Mars/Masterfoods a warning letter because the chocolate bar also contains 3.5 grams of saturated fat, an amount that contradicts its "heart health" claim. (The box recommends eating two servings a day - totaling 60 percent of a day's allowance of saturated fat - for a significant benefit.) The product remains on the market.

The CSPI has also filed a suit against Coca-Cola and Nestlé, manufacturers of Enviga, a green-tea soft drink that claims to speed the metabolism but which has produced only limited clinical evidence.

"The study they did was on 31 skinny young men and women and it lasted three days," says Schardt. "To get the effects you also need to drink three cans of this drink a day, which can add up to over 100 dollars a month. That's a lot of money to spend when there's no proof of this product's long-term effect." Another concern is that a can of Enviga contains 300 milligrams of caffeine - the equivalent of nearly nine cans of Coca-Cola.

Consumers should approach functional foods with caution. When in doubt, try to obtain nutrients from their original sources, says Dorothy Blair, an assistant professor of nutritional science at the Pennsylvania State University. Just because a phytochemical in a natural food is proven to have a benefit doesn't mean it will work in the same way in isolation.

"When you talk about health, kale is the perfect vegetable. But in every vegetable you have a thousand diverse chemicals that may augment each other, and there's only so many we can study."

"Some of these products may make sense for some people," says Grotto. "But what we have to make very clear is the promise of the functional food compared to the realities of research."

Lisa Jones, a Philadelphia-based dietician, warns consumers to look closely at labels. In the case of Tropicana's Healthy Heart juice, for instance, the recommended serving is eight ounces, two ounces more than the standard variety. That could mean excess calories.

"Look at the label for the first five ingredients. If something says it has fiber but it appears at the bottom of the list, you may be better off getting [fiber] elsewhere."

As the food-as-medicine market swells, functional foods are popping up all over, in Diet Coke and even vitamin-fortified beer.

Are these items a boon or just another way to lure consumers?

"If you're only drinking Diet Coke , switching to a vitamin-fortified version could help," Jones concedes. However, she wouldn't recommend drinking Diet Coke just to get your vitamins.