Several different fungi contribute to digestive system diseases by __________.

The question seems incomplete as it doesn't specify what information is needed about the fungi that contribute to digestive system diseases. However, I can provide a general answer:

Several different fungi contribute to digestive system diseases by disrupting the normal balance of gut flora. This can occur when an individual takes antibiotics, which can kill beneficial bacteria that keep fungi in check. Without these bacteria, fungi can multiply and cause infections. Some fungi produce harmful substances known as mycotoxins that can damage the lining of the gut. Others can cause inflammatory responses that lead to chronic gastrointestinal disorders. In severe cases, some fungi can invade the walls of the intestine and spread to other parts of the body.