Sodium bicarbonate supplementation in elite rugby players increases the frequency and severity of gastrointestinal symptoms during high-intensity training over time, and this time-dependent intolerance impairs performance through discomfort.

When sodium bicarbonate is swallowed, it reacts with stomach acid to produce carbon dioxide gas and water, causing the stomach to swell and stretch. This stretching activates nerves in the gut wall that send pain signals to the brain. At the same time, the excess bicarbonate alters the balance of acid and base in the intestines, which changes how the gut moves and how sensitive it is to pressure. As exercise continues, the body’s natural stress response increases gut movement and reduces blood flow to the intestines, making the swelling and nerve signals worse over time. This leads to increasing discomfort during high-intensity training.