Ralston Purina Co. wants you to know that its Oat Chex bran cereal may help reduce cholesterol levels when included as part of a low-fat diet.

The Food and Drug Administration wants you to know that Ralston Purina may be stretching the truth.

In fact, the FDA thinks a lot of companies may have taken their zest to attach health claims to products a bit too far. Last week, the agency sent out letters to six companies, including Ralston Purina, accusing them of making false and misleading claims and warning them that punitive steps will be taken if the matter is not corrected.

The threat of enforcement comes as the FDA attempts to rein in what has become a litany of ad claims aimed at health-conscious consumers in recent years. Nearly 40 percent of new products and a third of the $3.6 billion spent on food advertising last year contained a health-related message.

By sending out the warning letters, the FDA is making its first real attempt to enforce new regulatory guidelines drawn up last February. Those guidelines limited to six the areas where health claims can be made -- such as the relationships of fiber to colon cancer and fats to cancer -- and said that to make those claims a firm has to show there is a consensus of scientific evidence proving their truthfulness.

What the industry has been doing ever since is testing these rules, by making claims that sit on the fringes of these six areas or by trying to pass off one or two scientific studies as representing a "scientific consensus."

So far, the battle promises to be lively. None of the companies contacted by the FDA has plans to pull its products or rescind the claims it makes in its ads. The firms said they will respond to the FDA's warning and hope to be able to discuss their cases with the agency.

"We were surprised that there were not inquiries or comments {before the letter} from the FDA regarding their reservations," said Edward Parker of Pacific Rice Produce, which makes a cereal that purportedly helps to lower cholesterol. "If they would have mentioned it we would have been more than happy to provide information."

Parker said a study conducted at the University of California at Davis Medical School supports the company's claims that its Vita Fiber Rice Bran can reduce cholesterol when part of a low-fat diet.

Ralston Purina has come under attack for two breakfast products, its Oat Chex cereal and Oatmeal Goodness Bread Wheat Oatmeal. According to the oatmeal label, "recent clinical research has shown that regular consumption of oat products ... may help reduce and control serum cholesterol levels. Other medical studies have linked lowered cholesterol levels to a reduction in the occurrence of coronary heart disease." The FDA calls that statement false and misleading.

Patrick Farrell, spokesman for Ralston Purina subsidiary Continental Baking Co., said the claims are supported by studies in Australia and the United States, and that they will remain on the boxes of its products.

Jeff Nesbitt, associate commissioner for public affairs of the FDA, said the agency's policy on health claims has been evolving for several years. "It was not a sudden move -- over the last two to three years, there has been a lot of discussion on health and diet."

The tougher stance by the FDA comes as welcome news to consumer groups. Bruce Silverglade, legal director of the Center for Science in the Public Interest, said that some companies have been reckless with the use of health claims. "We are very pleased the FDA decided to crack down. We hope the FDA takes additional actions against misleading health claims."

Some food companies, however, feel that the FDA does not need the new policy outlining six general claims that can be made. These are the relationship of fiber to colon cancer, fiber to heart disease, fats to cancer, fats to heart disease, sodium to high blood pressure and calcium to osteoporosis.

"The FDA currently has the authority to regulate truthful, accurate messages even without the new policy," said Celeste Clark, Kellogg Co. vice president of nutrition marketing. Kellogg will submit comments in support of the FDA effort to establish guidelines on health messages, Clark said.

"But we will also express our concern, one of which is the lack of preemptive authority over the states," she said. "There is a need to establish a national uniform basis for the messages."