Yes! In the gut. You see, our digestive tracts are host to about 100 trillion microorganisms and it takes a lot of energy and oxygen to keep them in control.
When the unfriendly anaerobic (oxygen intolerant) pathogens multiply out of control in our digestive system, they compete with the friendly bacteria and us for vital nutrients. Thus, alter our cravings and metabolism in their favour. Also, they damage our intestinal lining, as in the case of irritable bowel and leaky gut syndromes.