A new study has reported that mice fed a low-carbohydrate, high-protein diet had a lower incidence of mammary tumors than mice fed a Western-style diet, and that tumors already present had slower growth. The authors theorized that since cancer cells depend more on glucose more than do normal cells, a low carbohydrate diet might inhibit tumor progression compared to a typical Western diet. To avoid effects that might be induced by caloric restriction, the low carbohydrate diets were designed to have the same number of calories as the Western diet. This was accomplished by increasing the level of protein rather than fat since high fat diets have been reported to have tumor-promoting effects whereas high protein diets may have immune-stimulating effects, according to the authors. The Western diet consisted of approximately 55% carbohydrates, 23% protein and 22% fat, whereas the low carbohydrate diet contained 15% carbohydrates, 58% protein and 26% fat.

Both mouse tumors and tumors from implanted human breast cancer cells were found to grow more slowly in mice on the low carbohydrate/high protein diet compared to those consuming the Western diet. The tumor-bearing mice on both diets had similar body weights. The mice fed the low carbohydrate diet were found to have lower blood glucose, insulin, and lactate levels than the other mice. When the low carbohydrate diets were combined with a cell growth inhibitor and especially with the COX-2 inhibitor Celebrex (which reduces inflammation), additive anticancer effects were observed. Most strikingly, when mice genetically engineered to develop HER2 overexpressing mammary cancer, nearly half of the mice on the Western diet developed mammary tumors by the age of one year. On the other hand, no tumors were detected in mice fed the low carbohydrate diet. This difference was associated with weight gains in mice on the Western diet that was not observed in mice given the low carbohydrate diet. In addition, whereas only one mouse on the Western diet reached a normal life span (the others having died from cancer), more than half of the mice fed the low carbohydrate diet reached or exceeded their normal life span of approximately two years. The authors conclude that the study findings offer a compelling illustration of the ability of a low carbohydrate diet to restrict cancer development and progression in mice.

Comments regarding the study

The results of the study may reflect the benefits of eliminating the insulin and glucose surges that accompany high carbohydrate meals rather than benefits specifically attributable to a high protein diet. Most foods that have been found to be associated with reduced risk of breast cancer contain complex carbohydrates. On the other hand, many animal sources of protein have been found to promote breast cancer and other diseases. One study found that a low-carbohydrate diet based on animal sources of protein was associated with higher risk of death, whereas a vegetable based low-carbohydrate diet was associated with lower all-cause and cardiovascular disease mortality rates. Therefore, we caution breast cancer patients to focus on consuming healthy carbohydrates and proteins (see our recommended food list) and avoid or limit unheathful high carb and high protein foods (see foods to avoid). Please also see our article on how to optimize how to optimize your breast cancer diet.