When T. Colin Campbell wrote in his book The China Study:

We were finding that high protein intake, in excess of the amount needed for growth, promotes cancer. Like flipping a light switch on and off, we could control cancer promotion merely by changing levels of protein.

The effects of protein feeding on tumor development were nothing less than spectacular. … [In one experiment] all animals that were administered [the carcinogen] aflatoxin and fed the regular 20% levels of casein either were dead or near death from liver tumors at 100 weeks. All animals administered the same level of aflatoxin but fed the low 5% protein diet were alive, active and thrifty, with sleek hair coats at 100 weeks. This was a virtual 100 to 0 score, something almost never seen in research.”

I would never have dreamed that our results up to this point would be so incredibly consistent, biologically plausible and statistically significant.

Let there be no doubt: cows milk protein is an exceptionally potent cancer promoter.

He was criticized for not discussing aspects of cow’s milk and other animal foods which could confound the relationship between animal protein and cancer. Here’s an excerpt from an article by Campbell addressing this concern:

“The adverse effects of animal protein, as illustrated in our laboratory by the effects of casein, are related to their amino acid composition, not to the effects of pasteurization, homogenization, or of the presence of hormones, pesticides, etc. Even though pasteurization and homogenization may cause slight changes in the physical characteristics of proteins, I know of no evidence where amino acid contents are altered by these treatments. This is important because it shows that there will be no difference in the biological effects of animal based protein from grass-fed or feed lot fed animals. Moreover, the casein that we used in our extensive experiments was before hormones were introduced and before factory farming became the norm, thus it mostly represented animals that were grass fed.”
– Grass-Fed Animal Agriculture, T. Colin Campbell Foundation

Here’s Campbell in his own words, arguing that “casein (cows milk protein) is the most relevant chemical carcinogen ever tested.”

Dr. Campbell is not extremist or fringe. He spent his career as a biochemist, professor, and research scientist working within mainstream institutions … MIT, Virginia Tech, Cornell. He has “received over 70 grant-years of peer-reviewed research funding (mostly NIH), served on several grant review panels, lectured extensively, and authored over 300 research papers.” He doesn’t just talk about research, he conducts his own, and has had it published in professional, peer-reviewed journals. He has sat on boards and panels and has “actively participated in the development of national and international nutrition policy.”

And after all this, one of his primary messages is … Consumption of animal protein promotes development of cancer.  Consumption of plant protein does not:

Wheat and soy proteins for example did not stimulate cancer development and when wheat protein, which is deficient in the amino acid lysine, was replenished with lysine, it acted just like casein. There have been literally thousands of studies going back many decades showing a similar effect of animal and plant based proteins on body growth and other events associated with body growth–all resulting from their differences in amino acid compositions.

A problem with eating a low-carb diet is that, by default, it has you eating more fat and protein, and that protein is primarily derived from animal foods.

You’ve just been diagnosed with cancer. What should you eat? A low-carb, Atkins-like diet? A Paleo diet? A vegetarian diet? The Mediterranean Diet? It doesn’t matter? A group of researchers sought to answer this question by applying the precautionary principle to evidence for which a dietary influence on cancer risk was substantial. Their work was published last month:

Applying the Precautionary Principle to Nutrition and Cancer, Journal of the American College of Nutrition, 28 May 2014

The precautionary principle is a scientifically and legally defined concept based on the view that there is a social responsibility to protect the public from harm when investigation has found a plausible risk. It places the burden of proof on those recommending the risk.

For example, the current body of evidence indicates that dairy food increases the risk for prostate cancer.  Applying the precautionary principle would have us limit our consumption of dairy.  Those recommending consumption of dairy must show that it does not contribute to cancer.

Based on these researchers’ investigation, this is what you should, or shouldn’t eat (“where evidence is sufficiently compelling”):

• Limit or avoid dairy products to reduce risk of prostate cancer.
• Limit or avoid alcohol to reduce risk of cancers of the mouth, pharynx, larynx, esophagus, colon, rectum, and breast.
• Avoid red and processed meat to reduce risk of cancers of the colon and rectum.
• Avoid grilled, fried, broiled, and other meats (meat here refers to red meat, poultry, and fish) cooked at high temperatures to reduce risk of cancers of the colon, rectum, breast, prostate, kidney, and pancreas.
• Eat soy products. If comsumed during adolescence they may reduce risk of breast cancer in adulthood. Soy products may also reduce risk of recurrence and mortality for women previously treated for breast cancer.
• Eat fruits and vegetables to reduce risk of several common forms of cancer.

I’ve picked out some mechanisms:

• Dairy – Contributes to prostate cancer risk via a large calcium dose that suppresses vitamin D activation, and by the tendency of milk to increase serum IGF-I concentrations.
• Alcohol – Contributes to cancer risk via harmful effects of metabolites of alcohol such as acetaldehyde, via lipid peroxidation, and generation of free-radical oxygen species. Alcohol may also disrupt folate metabolism.
• Red and Processed Meat – Contributes to cancer risk via abundance of heme iron, nitrites, heterocyclic amine formation, and the overabundance of essential amino acids and other nutrients that promote cell growth.
• Cooked Animal Foods – Contain heterocyclic amines (HCAs) that are genotoxic, mutagenic compounds formed from creatine and amino acids in cooked skeletal muscle, increasing in concentration with longer cooking times and higher temperatures. The National Toxicology Program lists 4 HCAs as “reasonably anticipated to be a human carcinogens.”
• Soy – Reduces cancer risk via ability of genistein [a phytoestrogen] to increase apoptosis [cancer cell death] and to reduce cell proliferation and blood vessel growth and to modulate sex hormone effects. Soy and other legumes are high in beneficial antioxidants.
• Fruits and Vegetables – Reduces cancer risk via antioxidants which limit reactive oxygen species. Some components may have antitumor properties, such as glycosylates (a precursor to isothiocyanates) and indole-3-carbonol (precursor to 3,3′-diindolylmethane), which have been shown to induce phase II enzymes responsible for eliminating reactive oxygen species and repairing DNA systems. Some components in soybeans, green tea, turmeric, grapes, tomatoes, and other plant foods have the ability to regulate apoptosis, an important pathway for cancer prevention.

They conclude:

“Overall, evidence suggests that diets emphasizing foods from plant sources—vegetables, fruits, whole grains, and legumes — are associated with lower cancer risk.”