A diet low in carbohydrates and high in protein may reduce the risk of cancer and slow the growth of tumors already present, according to a study published in Cancer Research.
 
The study was conducted in mice but the scientists believe the strong biological findings warrant that a similar effect in humans can be considered. 

Researchers implanted various strains of mice with human tumor cells or mouse tumor cells and assigned them to one of two diets. The first diet, a typical Western diet, contained about 55 percent carbohydrates, 23 percent protein and 22 percent fat. The second, like a South Beach diet but higher in protein, contained 15 percent carbohydrates, 58 percent protein and 26 percent fat. They found that the tumor cells grew consistently slower on the second diet.

Mice genetically predisposed to breast cancer were also put on those two diets and almost half of them on the Western diet developed breast cancer within their first year of life while none on the low-carbohydrate, high-protein diet did.  Only one on the Western diet mice reached a normal life span, approximately 2 years, with 70 percent of them dying from cancer while only 30 percent of those on the low-carbohydrate diet developed cancer and more than half these mice reached or exceeded their normal life span. 

They also tested the effect of an mTOR inhibitor, which inhibits cell growth, and a COX-2 inhibitor, which reduces inflammation, on tumor development, and found these agents had an additive effect in the mice fed the low-carbohydrate, high-protein diet. 

"This shows that something as simple as a change in diet can have an impact on cancer risk," said lead researcher Gerald Krystal, Ph.D., a distinguished scientist at the British Columbia Cancer Research Centre.    Cancer Research editor-in-chief George Prendergast, Ph.D., CEO of the Lankenau Institute for Medical Research, who was not involved with the study, agreed. "Many cancer patients are interested in making changes in areas that they can control, and this study definitely lends credence to the idea that a change in diet can be beneficial." 

When asked to speculate on the biological mechanism, Krystal said that tumor cells, unlike normal cells, need significantly more glucose to grow and thrive. Restricting carbohydrate intake can significantly limit blood glucose and insulin, a hormone that has been shown in many independent studies to promote tumor growth in both humans and mice.

Furthermore, a low-carbohydrate, high-protein diet has the potential to both boost the ability of the immune system to kill cancer cells and prevent obesity, which leads to chronic inflammation and cancer.