We all worry about diet, and we should. The food we eat can have major impacts on our health. But you may have never thought that diet could influence your risk of developing colorectal cancer. A team of researchers, led by Dr. Alberto Martin at the University of Toronto, recently published an amazing study showing how diet, specifically the intake of carbohydrates (or “carbs”; like bread and pasta), is a major factor in the development of colorectal cancer. This is a big deal because in the western world a typical adult diet is 50% carbohydrates1. Previous studies have found a link between carbs and colorectal cancer2, but no one has been able to confidently suggest a reason why this is the case until now. Researchers in this study found that a specific nutrient that comes from a high carb “western diet” increases the likelihood of developing colorectal cancer.
This study used mice that were prone to developing colorectal cancer because they possessed gene mutations commonly found in human colorectal cancer. Experiments were done to see how changing the diet of these mice affects their tendency to develop cancer. The researchers measured this by counting the number of polyps (which are small tumor-like growths that can develop into full cancers) in the mouse intestines. The researchers subjected some mice to the “western diet”, with 58% of calories coming from carbs, and other mice to a low-carb diet in which only 7% of the calories came from carbs. Remarkably, the mice on the low carb diet had significantly fewer polyps. What this means is that lowering the intake of carbs reduced the risk of colorectal cancer in these mice.
The really exciting thing from this study came when the researchers asked what it is about low-carb diets that reduces the risk of colorectal cancer. They found that the decreases in cancer risk associated with the low-carb diet also occurred when certain intestinal bacteria were killed with antibiotics. Intestinal bacteria take in carbs that are difficult to digest and break them down into more easily digestible nutrients. The fact that low carb diets and killing gut bacteria both affect the development of colorectal cancer in the same way hinted that maybe there is a nutrient produced by the gut bacteria that increases the risk of cancer. The researchers found a nutrient, called butyrate, which was significantly reduced in the low-carb mice compared to the “western diet” mice. Remarkably, feeding the mice high amounts of butyrate, or injecting butyrate into the mouse colons, caused increases in polyp development. This was the result that tied everything together and provided a possible explanation of the results: mice fed the “western diet” developed more polyps because more carbs in the gut provided more fuel for the gut bacteria to produce butyrate.
While this is a really compelling explanation, more studies need to be done for us to make sure this is actually the reason why low-carb diets reduce cancer risk. This also does not mean that eliminating butyrate will prevent colorectal cancer or that if you eat a lot of carbs you should be scared of developing cancer. Genetics still play a huge role, remember that the mice in this study already had mutations that increased the likelihood they would develop cancer. What this study has done is provide one of the best explanations so far on how diet can influence cancer. It also opens the door to the possibility that manipulating butyrate, or nutrients like it, in humans might one day be a cancer therapy. My hope is that with more research like this, we may learn ways that people at high risk of developing colorectal cancer can reduce their cancer risk by doing something as simple as altering their diet.
This article was written by Mathew Hall. Mat is a Masters graduate currently working at the Hospital for Sick Children as a cancer researcher. To find out more about Mat and his research check out his bio on the Members page.
The article in question:
Belcheva, A. et al. Gut microbial metabolism drives transformation of MSH2-deficient colon epithelial cells. Cell 158, 288-299, doi:10.1016/j.cell.2014.04.051 (2014).
- Roy, C.C., Kien, C.L., Bouthillier, L., and Levy, E. (2006). Short-chain fatty acids: ready for prime time? Nutr. Clin. Pract. 21, 351–366.
- Gnagnarella, P., Gandini, S., La Vecchia, C., and Maisonneuve, P. (2008). Glycemic index, glycemic load, and cancer risk: a meta-analysis. Am. J. Clin. Nutr. 87, 1793–1801.