John Harvey Kellogg's writings on breakfast offer insight into his research on nutrition - for Kellogg, the morning meal is an essential part of caring for the digestive system.

Kellogg begins by stating that the colon is among the organs most commonly afflicted with disease, and that its care is vital for a person's general health. Through illustrations, we are shown how food passes through the digestive tract, and how eating the correct food at the right intervals is important to maintaining health. Breakfast is identified as the most important meal, being as it is the meal which commences each day.

Throughout the text, Kellogg identifies and discusses common maladies of the digestive tract, their causes and potential remedies. The building up of harmful bacteria in the gut is one such problem, and that different kinds of germs which contribute to this. Kellogg posits that maintaining a healthy gut free of harmful bacteria is crucial for avoiding indigestion and other ailments, and that certain foods can promote better health. Finally, Kellogg praises nuts as a source of protein and speculates that they will become a staple part of a health-conscious diet in future.