Multigrain, oat bran, cracked wheat, or seven-grain. Which has the heart-healthy whole grains recommended by the government?

To answer that question, the Food and Drug Administration on Wednesday came out with a new definition of whole grains.

The agency wants to make it easier for people to choose foods made from whole grains. The choice is not easy, given the bewildering array of slogans and logos in the supermarket.

For example, Cheerios and other General Mills cereals have their own "whole grain" emblem. Companies from Bruegger's Bagels to Snyder's of Hanover pretzels use black-and-gold labels shaped like a postage stamp saying a product is a "good source," an "excellent source" or a "100 percent source" of whole grains. Quaker Instant Oatmeal has a small green banner saying, "Made With Whole Grain Oats."

"It's very important that consumers are able to have a consistent and uniform terminology of what constitutes a whole grain," said Barbara Schneeman, director of the FDA's office of nutritional products, labeling and dietary supplements.

Whole grains are vital to a healthy diet, according to federal guidelines. They say three servings each day of whole grains will cut the risk of heart disease and type 2 diabetes. A serving is about an ounce — a half-cup of oatmeal, a slice of bread, a cup of cold cereal flakes.

While the FDA is trying to make things clearer for consumers, the agency seems to be causing confusion in the food industry. The definition is just a draft, but if the FDA makes its permanent, many companies may have to change their food labels.

The FDA says a company can make factual statements, such as saying a product has 100 percent whole grains or 10 grams of whole grains. But the agency says a product should not claim to be an "excellent" or "good" source of whole grains.

The FDA did not say whether companies should start changing their labels.

"We would have to look at a particular product to understand whether something is being used appropriately," Schneeman said.

The agency recently refused a request from General Mills to define an "excellent" or "good" source of whole grains, saying those terms apply to specific nutrients but not to whole grains.

The industry reacted cautiously.

People are bewildered by the clutter of claims in ads and on packages, said K. Dun Gifford, president of Boston-based Oldways Preservation Trust, a think tank. Gifford helped create the black-and-gold Whole Grains Council stamps, which he said offer simple descriptions, not scientific health claims, to help consumers.

Robert Earl, senior director of nutrition policy at the Food Products Association, said the FDA's move is "something we're going to need to digest and discuss among our members."

"The agency has certainly been clear in this document about what is a whole grain and what is not a whole grain," Earl said.

It is not clear whether the definition will last. The FDA opened a two-month comment period on it, but officials said they did not know when, or if, the change would go into effect.

The definition says a whole grain must retain its basic structure. It applies to corn, rice, oats and wheat and lesser-known cereal grains, such as bulgur, millet and sorghum. It does not include soybeans, chickpeas, sunflower seeds and other legumes or oilseeds.

The tricky part is what's done to the grain during processing. If it's intact, ground, cracked or flaked, it still is a whole grain. Rolled or "quick" oats are still whole grains. Popcorn is a whole grain. Pearled barley is not a whole grain; too much of its bran layer has been removed.

In addition, pizza or bagels labeled as "whole grain" or "whole wheat" ought to have dough made entirely from whole wheat or whole grain flour, the FDA said.