The speaker discusses the benefits of nasal breathing versus mouth breathing, emphasizing the importance of nasal breathing for overall health. This method filters and warms the air while increasing nitric oxide levels and helping retain carbon dioxide (CO2), which is crucial for oxygen transport in the body. By mouth breathing, individuals risk losing CO2, which can lead to lower oxygen levels, potentially causing feelings of lightheadedness or fatigue. The speaker notes that while nasal breathing can be practiced during everyday activities, it becomes challenging during high-intensity exercise where oxygen intake is critical. Instead, it is beneficial to engage in nasal breathing during moderate training to enhance aerobic capacity. The speaker shares personal experience with this technique, including a nose operation that affected their practice.