tracer food
Any food which exists the body in a condition which still allows for basic identification, particularly including foods difficult to digest like fibrous vegetables.
If you eat a tracer food like beets, you can gauge how long it takes for foods to pass through your system.
Tracer Food
Food that can be identified in fecal matter.
Mike took a huge dump and noticed the corn kernals from the corn on the cob he ate the day before.