Mayor Michael R. Bloomberg has become New York City’s nutritional nag, banning the use of trans fats, forcing chain restaurants to post calorie counts and exhorting diners to consume less salt. Now he is at it again, directing his wrath at sugary drinks in a new series of arresting advertisements that ask subway riders: “Are you pouring on the pounds?”

But an examination of what enters the mayoral mouth reveals that Mr. Bloomberg is an omnivore with his own glaring indulgences, many of them at odds with his own policies. And he struggles mightily to restrain his appetite.