You might be surprised to learn that the members of the bacterial population functioning in your gut could undergo changes that not only affect your health, but also adversely impact how your body responds to medicine. A recent Cell publication revealed that this can occur in patients with Type 2 diabetes (T2D), where certain foreign bacterial species are able to colonize the gut and produce the metabolite imidazole propionate from histidine (an amino acid that appears somewhat frequently in proteins). Researchers found elevated levels of imidazole propionate in T2D patients and showed that mice treated with this metabolite exhibited worsened glucose tolerance (increased insulin insensitivity) and inhibited signaling in cells that should occur in response to insulin. Studies such as this are crucial to better understand not only how our bodies respond to disease, but how changes in the microbes that reside inside us can also be affected and adversely impact prescribed treatments.