In Mary Roach's book "Gulp: Adventures on the Alimentary Canal," she delves into various aspects of food and digestion. One interesting historical reference comes from an 1859 edition of the California Farmer and Journal of Useful Sciences, which includes a recipe that utilizes Peruvian seabird guano to create a nutritional extract. This highlights the unusual and often unexpected sources of nutrition that have been explored throughout history.

The use of guano, primarily known as a fertilizer due to its high nitrogen content, exemplifies the innovative ways people have sought nutrition. Roach's exploration of such topics sheds light on the fascinating relationships humans have with food and the unconventional methods some have employed to enhance dietary intake.