Oster delves into the challenging topic of breastfeeding, sharing her personal experience and emphasizing that it can be a difficult journey for many women, contrary to the idealized image often presented. She discusses the various struggles she faced, such as supplementing with formula, using elaborate feeding setups, and the challenge of getting her baby to latch.

Oster then presents a comprehensive list of the claimed benefits of breastfeeding. She critically examines the challenges of conducting studies on breastfeeding due to inherent biases, such as more educated and wealthier women being more likely to breastfeed. Oster introduces readers to a variety of research methods, emphasizing the importance of randomized controlled trials in providing stronger evidence. She discusses the Promotion of Breastfeeding Intervention Trial (PROBIT) in Belarus, highlighting its findings on the impact of breastfeeding on gastrointestinal infections, eczema, and other health outcomes.

The author explores the relationship between breastfeeding and Sudden Infant Death Syndrome (SIDS), shedding light on the challenges of studying this rare but devastating occurrence and expressing caution about drawing definitive conclusions from existing data.

Moreover, Oster highlights that while many people claim breastfeeding leads to long-term advantages such as increased intelligence and reduced risk of obesity, the evidence supporting these assertions is not compelling.