Low-Carb Diets May be Linked to Bowel Cancer

By Dietitian, Juliette Kellow BSc RD

Low carb diets such as Atkins have received a lot of bad press in the past few years. Now a new study from the Rowett Research Institute in Aberdeen suggests they may be linked to an increased risk of bowel cancer.

Researchers gave 19 obese men a high carbohydrate diet (399g a day) for 3 days, followed by a medium carbohydrate intake (164g a day) for a month and then a very low intake of carbohydrate (24g a day) for another month.

At the end of each study period, researchers collected stool samples and measured levels of a fatty acid called butyrate. This fatty acid is produced by bacteria in the gut and helps to kill cancerous cells. The scientists discovered that low-carb diets were linked to a reduction in gut bacteria. Furthermore, there was a four-fold drop in cancer-fighting butyrate between the high carb diet and the low-carbohydrate diet.

Speaking of low-carb diets, Professor Harry Flint who led the research says, “In the long run, it is possible that such diets could contribute to colorectal cancer.”

Dietitian, Juliette Kellow says:

With just 19 men, this is only a small study but the findings are interesting and should provide the basis for some larger scale research. The theory might sound complicated but it actually makes sense. With a normal diet that contains good amounts of carbs, some of the components of these carbs such as dietary fibre and resistant starch aren’t digested and so pass into the large bowel. Here, they provide food for good gut bacteria such as bifidobacteria. These good bacteria ferment the undigested carbohydrates, creating short chain fatty acids such as butyrate in the process – and butyrate is thought to protect again colorectal or bowel cancer.

With a diet that contains just tiny amounts of carbs, virtually no undigested carbohydrate passes into the bowel. This means the good bacteria have less food and so die. As a result, butyrate levels drop, potentially increasing the risk of cancer.

Many larger studies have provided good evidence to suggest that eating carb-rich foods – particularly wholegrain carbs – may help to protect against bowel cancer.

In a recent study published in the American Journal of Clinical Nutrition, a good intake of wholegrains was found to reduce the risk of colorectal cancer by 21 percent. Similarly, fruit and vegetables have been linked to a lower risk of bowel cancer.

With a very low carb intake, you have to restrict wholegrains, fruit and often veg. Therefore, it makes sense that a low carb diet might increase the risk of bowel cancer.

WLR’s Advice:

Ditch low-carbohydrate diets once and for all and instead follow a healthy eating plan with carb-rich, wholegrain foods such as wholegrain cereals, oats, wholemeal bread, brown rice and wholewheat pasta.

Always eat five servings of fruit and veg a day, not just for helping to protect you from cancer, but also because they fill you up and provide a range of vital nutrients.