Our gut is our body's most immunologically active organ, communicating with different organ systems. What we consume in our gut acts as the entry point to several systemic connections. The gut-X axis denotes the axis or connections by which the gut communicates with various systemic organs or functions. The X could stand for the lungs, such as in the gut-lung axis, the heart in the gut-heart axis, the brain in the gut-brain axis, and so forth.