Now that secularism is predominant in the post-Modern world, many people reject institutional religion but not spirituality or the practices associated with formal religion. Fasting has made a comeback as individuals recognize the benefits of the practice, but many world religions have advocated sound health for centuries. The author explores the history and science behind the religious practice.

Self-deprivation is unremarkable in religious contexts and spirituality has long advocated abstinence from sex, drink, sleep, or food. Today, fasting has returned mostly for secular and health-related reasons, or as a departure from a person's daily routine.

In the volume, the author interviewed practitioners of fasting and engaged in fasting himself as self-discovery. The survey of history includes a notable list of exemplars who fasted including: Moses, Buddha, Jesus, Muhammad, Gandhi, George Washington, Abraham Lincoln, Emily Dickinson, Mark Twain, Cesar Chavez; moreover, fasting has been adopted by religions and political movements all over the world for millennia. Fasting is central to holy seasons and days such as Lent (Christianity), Ramadan (Islam), Yom Kippur (Judaism), Uposatha (Buddhism), and Ekadashi (Hinduism). On an individual level, devout ascetics who master self-deprivation to an extreme are believed to be tuned into the divine, ascending to enlightenment or even sainthood.

In addition, The Fast considers complex science at the heart behind the biological phenomena that occur inside the human body when we fast. Metabolic switching induced by fasting can prompt repair and renewal down to the molecular level; such fasting can provide benefits for those suffering from obesity and diabetes, cancer, epilepsy, cardiovascular disease, neurodegenerative disorders, and more. Prolonged fasting can serve both to reinvigorate the immune system and to protect it against damage.

The author alludes to the political aspect of fasting—a hunger strike—which has signaled purity of intent and action. It’s a tactic that has provoked a response to individual commitment, focusing on an unjust system. Advocates who have waged hunger strikes include Gandhi in India, Bobby Sands in Ireland, and the Taxi Workers Alliance in New York City.

Fasting is a determined stance, a commitment, and a hearkening to a basic survival mode. The practitioner is focused on basics and mastery of one's body. Practiced well, it can be ultimately empowering.