Advertising is also regulated, by the government. The same one that regulates what goes inside of food. If the public is vulnerable to manipulation by advertising, the government is also vulnerable to manipulation by lobbying (remember the USDA "food pyramid" that put grains at the bottom due to industry lobbying?). Your argument is inconsistent because it implies that the government is somehow both simultaneously going to allow the public to be deceived by advertising, but correctly regulate the contents of food itself.