Professor Campbell (the author of 'The China Study') is one of the leading nutrition epidemiologists in the United States and the World. His work is impressive, and his results make it clear that eating more protein is correlated to significantly increased disease risk. However, epidemiology can not show causation. Correlation only shows an ASSOCIATION. A thorough search through the literature shows that how protein sources are cooked (BBQ, high-temperature stir frying, any form of cooking that blackens or darkly browns food) increases its carcinogenicity. And the TYPE OF FATS that are in many protein sources (saturated fats in animals and animal products) negatively impacts circulatory health (increasing atherosclerosis and therefore heart disease, stroke and high blood pressure). Studies looking at high temperature cooking (stir frying) just ONCE PER DAY in China (research not done by Prof. Campbell) showed TWICE the risk of lung cancer [Lung Cancer 35 (2002) 111] and preferring heavily browned (charred) foods increases colorectal cancer risk by a factor of 5 [Nutrition 20 (2004) 873] to 6 [Int J Cancer 49 (1991) 520]. So should we just not over-cook our meats? Yes, that would help a lot, but large amounts of meat regardless of how it is cooked still results in excess saturated fat in the diet and therefore circulatory disease. So should we eat low-fat meats and not overcook them? Yes, this is better still. But hormones in chicken may in the future be shown to cause problems (this has not yet been shown) and deli meats, regardless of their fat content, cause colorectal cancer because of the preservatives that they contain [Int J Cancer 119 (2006) 2657 and Cancer Epidemiol Biomarkers Prev 10 (2001) 439]. Taking up another notch, eating protein sources containing UNSATURATED fats is the healthiest approach, but many types of fish contain mercury (see my mercury article in the downloads page of my web site www.DrClydeWilson.com) and soy has some potential negatives when consumed in very large amounts (see my article on soy in the "specific foods" category of this blog). I think that the best conclusion we can draw is that food not contaminated (e.g. mercury), over-processed (trans fats, added sugars in products), over-cooked (produces cancer-causing agents), or eaten in very large amounts (even excess omega-3 fats in and of itself increases circulatory disease even though smaller amounts reduce risk) can cause problems. The healthiest diet is one that includes a BROAD spectrum of foods in BALANCE with each other WITHOUT any extreme approaches. Another good example involves whether or not you should cook your vegetables: Cooking vegetables a bit INCREASES their bioavailability because it breaks down the plant cell wall, whereas cooking beyond ten minutes or so simply continues to destroys nutrients. There are no absolutes as far as I can tell in nutrition. Moderation is the most scientifically sound approach shown to date. So does protein cause cancer? No: Amino acids have not been shown to induce cancer. Yes: Diets high in protein are CORRELATED to increased cancer for several complex reasons. While I do not know what Prof Campbell wrote in his China Study BOOK, I do know that in looking at his peer-reviewed published scientific papers he does NOT say that protein causes cancer. If he had, the reviewers sent it back to him, telling him to change it before they would publish it. Epidemiology can not show causation. But his work is critically important to get us moving towards understanding why diets high in protein are associated with so many problems. On the flip side of this, cutting out all protein reduces health since the body can then not make enough new proteins (you need at least 10% of calories to be bioavailable protein) and eating only "healthy protein sources" (fish or tofu) does not come completely without risk. In summary, I do agree that a primarily plant-based diet is the healthiest, but I believe this for many complex reasons beyond just avoiding protein.