In "Gulp: Adventures on the Alimentary Canal," Mary Roach discusses the breath hydrogen test used to measure gas production in the human body. This test allows researchers to determine the amount of hydrogen someone exhales through their breath, which can be correlated with the hydrogen produced in the colon. Since a set amount of this gas is absorbed into the bloodstream and later exhaled, it's possible to estimate gas production without the need for more invasive or awkward methods.

This approach provides a straightforward and reliable means to study intestinal gas without requiring the subject to expel gas into a collection device. The breath hydrogen test has become an essential tool for researchers exploring gastrointestinal processes, offering insights that help us understand digestive function and the factors influencing gas production.