The San Francisco attorney general’s staff recently sent a warning letter to Kellogg’s concerning the manufacturer's claims that eating its cereal products will boost immunity, according to a recent post on Food Politics, a blog by author and public health nutrition expert Marion Nestle.

The letter comes on the heels of a food industry group’s recent decision to voluntarily halt promotion of its nutrition labeling program known as “Smart Choices” after federal regulators said such systems may be misleading consumers, according to the Associated Press.

 According to the AP, “Smart Choices, which includes nine major companies such as Kellogg Co., Kraft Foods Inc. and General Mills Inc., has been criticized for handing its green seal to processed foods that are high in sugar, such as Froot Loops cereal and Cracker Jack snack food.”

As a result of the industry's flimsy claims, the FDA wrote a “Dear Industry” letter in October that says it will be creating standards for front of package or FOP labeling, reported MNN blogger Robin Shreeves.

Not long after, Smart Choices officials in Washington, D.C., said the group will "postpone" active operations and not encourage wider use of the logo while the FDA investigates the issue, according to the AP story.

Though Kellogg's has promised to phase out the Smart Choices labeling on its products, the cereal manufacturer is again feeling heat for flimsy health claims, this time from San Francisco city attorneys.

In a letter to Kellogg’s, the city of San Francisco alleges that the claims, “Now Helps Support Your Child’s Immunity”, located on the front of the cereal box packages, and “[N]ow each and every box is fortified with vitamins and nutrients that work together to help support your child’s immunity” on the company Web site, are misleading.

The staff members wrote, “At a time when parents are increasingly worried about the spread of the H1N1 virus (“swine flu”), it is vitally important that parents receive accurate information about what they can do to protect their children’s health. Thus, in addition to constituting a potential violation of California’s Unfair Competition Law, the Immunity Claims may undermine critical public health efforts to prevent the spread of a disease that the President has declared to be a national emergency.”

In other words, Kellogg's could be in some hot water if it can't back up its immunity claims. 

In order to validate the claims, which are sold in the city and county of San Francisco as well as across the country, the attorney general’s staff requested that Kellogg's “provide evidence of the facts upon which Kellogg’s Immunity Claims are based.”

There’s no word yet on how Kellogg’s plans to respond to the requests, but it will be interesting to see what, if any, scientific studies there are to confirm that eating sugary, highly processed cereal can actually keep people from getting the flu.

In the meantime, those who want to boost their immunity in ways that have been scientifically validated should check out MNN’s list of 10 flu-fighting foods.