STORY AT-A-GLANCE

• Your gut is home to bacteria, viruses, fungi, archaea and eukarya; bacteria make up the vast majority of microbes in your microbiome
• While your highly acidic stomach may host only about 1,000 colony-forming units (CFU) of bacteria per milliliter (mL), your large intestine is home to up to 1 trillion CFU/mL
• Bacteroides are the dominant microbe in your large intestine; the composition of these microbes, and those elsewhere in your gut, are linked to health conditions like obesity, depression, Alzheimer’s disease and inflammation
• Your age, health status, diet and environment all influence the numbers and diversity of microorganisms in your gut
• A healthy gut microbiome depends on the consumption of whole, fermented foods and the avoidance of unnecessary antibiotics and other environmental assaults; spore-based probiotics are one option to help