University of Virginia researchers have found that cancer treatments can be significantly affected by diet, increasing the the toxicity levels of chemo up to 100 times. 

Diet affects our gut bacteria and the researchers found that even small changes like the addition of a single amino acid can have a significant impact. 

There is little research performed on diet and cancer therapy and the investigators were surprised to see the differences small changes in the microbiome mcould make. Study author Eyleen O’Rourke, PhD of the UVA College of Arts & Sciences in the School of Medicine’s Department of Cell Biology said: 

"The first time we observed that changing the microbe or adding a single amino acid to the diet could transform an innocuous dose of the drug into a highly toxic one, we couldn't believe our eyes. Understanding, with molecular resolution, what was going on took sieving through hundreds of microbe and host genes. The answer was an astonishingly complex network of interactions between diet, microbe, drug and host.”

The study, published in Nature Communications, found that common elements of our daily diets like amino acids could increase or decrease the toxicity of chemotherapies used in cancer treatment. This may provide insight as to why some patients respond to chemotherapy in different ways. 

The researchers used a simplified model - roundworms were used as the host and non-disease causing E coli bacteria were used to represent the microbiome. Wenfan Ke, a graduate student said: 

"The same dose of the drug that does nothing on the control diet kills the [roundworm] if a milligram of the amino acid serine is added to the diet.”

Serine is a naturally occurring amino acid. This means that diet interactions with the gut microbiome can alter a patient’s response to the drugs without changes in the drug or in the patient. 

“Humans host more than 1500 species in the gut, and the composition varies between and within individuals. Each of these microbes can distinctly metabolize dietary components and drugs. The dietary nutrient and drug derivatives from each microbe can be further metabolized or alter the physiology of other microbes and the host, building chains of events alternatively or simultaneously triggered by dietary, drug, microbe and host metabolites, byproducts, and signaling molecules.”

The researchers suggest that the complexity of the interactions among drug, host and microbiome is likely "astronomical." Much more study is needed, but the resulting understanding, they say, will help doctors "realize the full therapeutic potential of the microbiota."