What can cause loss of appetite and nausea in a male?

Same as a female...: ...Except pregnancy! the GI tract has a very limited # of symptoms to signal its distress--nausea/vomiting, diarrhea/constipation, bloating, pain, fullness, bleeding, etc. Many of these characterize ibs, but are also seen with inflammatory, infectious, ischemic, malabsorptive, & functional disorders. Directed lab work, imaging, biopsies, stool studies will find your answer & direct treatment.