Macfadden popularized the practice of fasting that previously had been associated with illnesses such as anorexia nervosa. He felt strongly that fasting was one of the surest ways to physical health. Many of his subjects would fast for a week in order to rejuvenate their body. He claimed that “a person could exercise unqualified control over virtually all types of disease while revealing a degree of strength and stamina such as would put others to shame” through fasting. He saw fasting as an instrument with which to prove a man's superiority over other men.
Macfadden had photographs of himself taken before and after fasts to demonstrate their positive effects on the body. For example, one photograph showed Macfadden lifting a 100 pound dumbbell over his head immediately after a seven day fast. He also promoted fasting by appealing to racial prejudices, suggesting that fasting was a practice of self-denial that only civilized white men would choose to embrace. Macfadden acknowledged the difficulties of fasting and did not support it as an ascetic practice but rather because he believed its ultimate benefits outweighed its costs.
He was particularly opposed to the consumption of bread, which he called the “staff of death.”