At one time, the role of gut bacteria in human health was marginalized as a side note that health experts found interesting but not integral. But as more and more research has made clear, the number and diversity of bacteria in the gut can often make the difference between health and disease. Two new studies have found that gut bacteria can also determine the effectiveness of the treatments that are used to fight cancer, forcing doctors to take a closer look at the lessons they can learn from this once overlooked aspect of human health.

In one experiment, researchers at the University of Lille in France looked at ipilimumab — a cancer drug used to treat advanced melanoma — and found that not only did the medication affect the amount of bacteria that was in the gut, but its own effectiveness went hand-in-hand with the level of bacteria trial participants had in their intestines. So the very drug that needed gut bacteria in order to work was the thing that was destroying participants' gut bacteria levels. Researchers found that when they gave participants supplemental levels of bacteria along with ipilimumab, they responded better to treatment.

A second study — conducted by researchers at the University of Chicago — confirmed the importance of gut bacteria in cancer treatment. For this study, researchers looked at the growth of tumors in two sets of animal subjects and compared that to the profile of bacteria in their intestines. Researchers found that mice who had the bacteria Bifidobacteria in their guts had slower tumor growth than those who did not. When the team transplanted this bacteria into the intestines of the mice that did not have it, they too experienced slowed tumor growth. And this was without any additional drug or treatment.

The takeaway from these two studies is that gut bacteria is very important in the treatment of disease. Of course, both of these studies were conducted on mice, so more work needs to be done to further define the role of gut bacteria in human health. But even at this stage of the game, many health experts are recommending that health care providers evaluate gut bacteria for their patients before beginning any type of treatment and replenish bacteria as necessary to improve the effectiveness of treatment.