An Iowa State University Food Science and Human Nutrition professor says there are drawbacks for those committed to eating only so-called "clean food." Ruth MacDonald says no specific definitions or guidelines are available for consumers to follow to avoid foods with additives, preservatives or other chemicals. She says some of those hard-to-understand chemicals on food labels are natural occurring and important for proper nutrition. MacDonald also says food companies claim their products contain no synthetic nitrates but they'll often replace them with natrually-occuring nitrates, which are chemically the same.