Restricted protein intake may prevent cancer

From foodconsumer.org

By Sue Mueller
July 6, 2006

Carcinogens are needed to initiate carcinogenesis. But people sometimes ignore the fact that exposure to carcinogens does not necessarily lead to the development of cancer. Scientists know environmental factors are important determinants for the cancer risk, but many may not know the diet a person uses may have an important effect on his cancer risk.

Among many nutrients, protein as a micronutrient may play a significant role in the cancer development. The type of protein one eats may determine his risk of cancer in his life time because some proteins are actually promoters of cancer growth, according to a book titled The China Study published in 2005 by Benbella Books.

The book was authored by Dr. T. Colin Campbell, who retired not long ago as a nutrition professor from Cornell University and Thomas M. Campbell II. It is largely based on Dr. Campbell's 35-year research on the relationship between nutrition and cancer risk. The book reports many findings derived from DR. Campbell's studies of the proteins' effect on cancer risk. In a word, animal proteins promote cancer growth while plant proteins do not.

The detailed evidence revealed in the book is extremely provocative as many people, not to mention the industries, may not like to hear it because it suggests what Americans eat may be totally in favor of cancer development.

In the U.S., 40 percent of the population is expected to develop one type of cancer or another in their life time. The book suggests the high incidence of cancer in the U.S. may be attributed at least in part to the Western diet which is characterized by high fat and high animal protein.

Dr. Campbell found that animal nutrients including protein, casein in particular and other nutrients are promoters of cancers while plant proteins such as soy protein and wheat protein gluten do not have a promoting effect on cancer. The finding suggests those who want to lower their risk of cancer may consider a vegetarian diet with no protein from any animal source.

According to the book, limited protein intake can actually keep cancer cells from developing into clinically significant cancerous mass called cancer. One of Dr. Campbell's animal studies found that a diet with 5 percent of the total calories from protein can lower the activity of an enzyme that can convert aflatoxin into a toxic form that leads to liver cancer. In comparison, when rats were fed a diet with 20 percent protein (casein), the enzyme activity increased by 76 percent. This study demonstrated that the low protein diet may slow the initiation stage of the cancer development.

In another amazing study, Dr. Campbell's team exposed rats to aflatoxin and then fed them with either a diet with 5 percent protein or a diet with 20 percent casein for 100 weeks, almost life time for rats. They found that all of those on the high casein diet died or nearly died from liver tumors at 100 weeks while all of those who were on the low protein diet were still "alive, active and thrifty, with sleek hair coats at 100 weeks."

The results indicate two aspects of one fact that exposure to carcinogens may be less likely to cause cancer in a person whose diet contains a sufficiently low protein. Furthermore, the study also found those rats that initially were on the high protein diet, but shifted halfway to the low protein diet were found to have fewer cancers (35 to 40 percent less). In comparison, those who were initially on the low protein diet, but at 50 weeks shifted to the high protein diet started developing cancers. The results suggest a low protein diet can also have a protective effect against the promotion and progression stages in the cancer development.

Dr. Campbell's studies found that low protein diets can not only lower the activity of an enzyme that converts non-toxic chemicals such as aflatoxin into a toxic form, but also help prevent toxins from entering cells, slower the cell multiplication and protect against the formation of toxin-DNA adducts.

When a high protein diet is used, the toxicity of aflatoxin increases as the dose increases. But when the protein is limited at 5 percent in a diet, the toxicity of aflatoxin remains minimal. The adequate percentage of protein for body growth is 10 percent. Luckily, the cancer risk drastically increases only when the protein content exceeds 10 percent.

All the studies indicate that high intake of casein, which accounts for 87 percent of dairy protein, promotes cancer development. According to Dr. Campbell, low protein diets have a protective effect against the cancer in all three stages of cancer development, namely initiation, promotion, and progression.

Although many Dr. Campbell's studies were on aflatoxin, the effect of the animal protein on cancer risk may as well be applied to other agents which may or may not have to be converted into a toxic substance during the detoxification in the liver. For instance, Dr. Campbell's team found that hepatitis B virus, which is known to be a carcinogen that causes liver cancer, does not cause as much damage in rats fed a diet with 5 percent protein as in rats fed a diet with 20 percent protein.

All the studies were conducted in animals. But the China Study conducted by Dr. Campbell and colleagues revealed that intake of animal protein and other animal nutrients might be a key factor affecting the cancer risk in humans. In China, incidence of cancer in one county can be 100 times higher than that in another county. The difference in cancer risk was linked to the difference in the diet.

Compared to the US, China has a much lower incidence of cancer, at least so a decade ago. The Chinese on average eat no more than 10 percent of protein from their diet, among which about 90 percent of protein comes from plants. In comparison, Americans eat more than 15 percent of protein in their diet, among which more than 80 percent comes from animals. According to the book, the difference in protein content may cause at least seven-fold difference in cancer risk. This difference might explain why there are so many cancer cases in the U.S. while the Chinese has much low incidence of cancer.

When it comes to the effect of dietary protein on cancer risk, Dr. Campbell's findings are not alone. Other researchers also found that a diet with high animal protein increases risk of breast cancer, according to Dr. Campbell's book. Epidemiologic studies have linked red meat and processed meat to an elevated risk of colon cancer. Link between dairy products and prostate cancer has also been established. According to the book, not just protein, other animal nutrients may also be risk factors for cancer.

Dr. Campbell's findings of the effect of animal protein and other animal nutrients on the cancer risk are so convincing that they have turned Dr. Campbell and his family into vegetarians. A low protein diet with a capacity of lowering cancer risk may not be adopted by everyone. But those who are flexible enough to adopt a vegetarian diet may have a good alternative to maximally avoid the risk of cancer. This is important for two reasons: 1) Current conventional cancer treatments are unable to render any cure for any cancer, and 2) exposure to environmental risk factors is unavoidable anywhere.


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