An edible negative contrast agent for CT imaging of the gastrointestinal tract intended for oral intake. The contrast agent is a fluid, aqueous foam displaying a CT density contrast value in the range -300 to -800 HU and having a consistency of 7 to 12 cm as measured with Bostwick consistometer. The contrast agent comprises an aqueous continuous liquid phase having a pH of 6.5 to 8.0 and gas bubbles dispersed in the continuous aqueous liquid phase. The aqueous continuous liquid phase comprises a surfactant, the surfactant being a protein, a hydrocolloid acting as foam stabilizer, a buffering agent, and water.
