Diet also plays an important role in the development of cancer. Protein as a micronutrient may play a significant role in the cancer development.
It is found that some proteins are actually promoters of cancer growth. In the book titled The China Study which is published by Benbella Books and authored by Dr. T. Colin Campbell a detailed analysis of the existing relationship between nutrition and cancer risk is evident. Dr. T. Colin Campbell a nutrition professor from Cornell University in his book reports about how animal proteins promote cancer growth while plant proteins do not. He also says in the book that the American diet is in favor of cancer development. Statistics show that about 40 % percent of the population in the US is expected to develop one type of cancer or another in their life time.
This is because of their western diet which is characterized by high fat and high animal protein. Animal nutrients such as casein and other nutrients are found to be promoters of cancers while plant proteins such as soy protein and wheat protein gluten do not have a promoting effect on cancer. He says that vegetarian diet with no protein from any animal source reduces the risk of cancer. In one of the author's animal studies it was found that a diet with 5 % of the total calories from protein lowers the activity of an enzyme that can convert aflatoxin into a toxic form that leads to liver cancer.
On the other hand when the rats were fed with 20 % casein the same enzyme activity increased by 76 % resulting in an increased risk of cancer. Hence the author concluded that exposure to carcinogens may be less likely to cause cancer in a person whose diet contains a sufficiently low protein. The results suggest a low protein diet can also prevent toxins from entering cells, lowers the cell multiplication rate and protects against the formation of toxin-DNA adducts. He also mentions that the adequate percentage of protein for body growth is 10 %. Dr. Campbell's team also found that hepatitis B virus, which is known to be a carcinogen that causes liver cancer, does not cause as much damage in rats which were given a diet with 5 % protein when compared to rats fed with a diet containing 20 % protein.
The Chinese on average consumed less than 10 % of protein from their diet, among which 90 % of protein comes from plants. On the other hand Americans consumed more than 15 % of protein in their diet, among which more than 80 % comes from animal source. This difference in protein content may cause at least seven-fold difference in cancer risk. A diet with high animal protein increases risk of breast cancer. Similarly a diet rich in red meat and processed meat resulted in an elevated risk of colon cancer. Link between dairy products and prostate cancer has already been established.