Foul-smelling stools are one of the most common symptoms of certain health conditions. They may be triggered by certain foods you eat or medications that you take.
Some foods are hard to digest, which makes them harder for the bacteria in your large intestine to break down. These include meats, dairy, eggs, garlic, and cruciferous vegetables (think: broccoli, cabbage, and kale).
This extra work means your stool will have more of the gases that make it smell a bit funky. These include odorless hydrogen and carbon dioxide gas, as well as methane and odorous hydrogen sulfide.
Other foods that make your stools smell bad are those that are high in sulfur. Sulfur-metabolizing bacteria in your large intestine can't break down these foods as efficiently, which leads to even more of those sulfur gasses in your poop.
Another possible cause of foul-smelling stools is an inflammatory bowel disease, such as Crohn's disease or ulcerative colitis, per the Mayo Clinic. These disorders can cause your intestines to swell and become inflamed, which can lead to excess fat in the stool and make it smell.
Other causes of atypically foul-smelling stools can include intestinal infections and diseases that affect your ability to absorb nutrients from your diet, such as celiac disease or short bowel syndrome. Symptoms include diarrhea, vomiting, stomach pain, and fatigue.