T Colin Campbell’s book The China Study summarizes his journey starting with basic science research in the effects of nutritional changes in laboratory animals and ends with what is likely the largest observational study on nutrition and health ever conducted.
The book is based upon a published research article concerning the same information. In this article an enormous number of factors where studied in relationship to a populace’s nutritional intake. The conclusion made by Dr Campbell is that a plant based diet devoid of animal protein of any kind, milk, and oils provides the best possible diet to reduce one’s risk of developing cardiovascular disease or cancer. This is essentially the same hypothesis presented by Dr Dean Ornish and Dr Caldwell Esselstyn in their books.
Dr Campbell provides some compelling theories in his book but ultimately I find several short comings. First, he bases his study findings on blood that has been pooled for easier study. In this approach he is able to simplify the bench work required to process so many blood samples but it may falsely alter his results and correlation. As many other authors have pointed out when the original data is examined it often tends to point in a different direction than Dr. Campbell’s hypothesis.
Second, correlation does not provide causation. Acknowledging that a particular people group eats a particular diet and has a low or high risk for a disease does not indicate that the two factors are necessarily related. That is the critical element that observational studies like this one simply cannot prove. They provide wonderful information with which to develop causal theories but cannot provide causation. There are just too many variables unaccounted.
Lastly, Dr. Campbell glosses over the critical missing element of an all plant diet. That is, what to do about nutrients that only come from animals. Of the four he discusses (cholesterol, vitamin A, vitamin D, vitamin B12) only two are challenges in my mind for the modern day plant eater.
Vitamin D is a substance easily made in the skin of most people when exposed to sufficient levels of UVB irradiation. It is often found in the oils of many saltwater fish including salmon and tuna. Dr. Campbell contends that people can make enough vitamin D if they receive regular sun exposure. He argues that humans do not require additional intake in their diet from animals. However, in my professional experience I find almost no patients who have a naturally normal level of vitamin D. Even those that receive above average levels of sun exposure such as roofers and outdoor landscapers tend to have subpar vitamin D levels. Many studies confirm that it is difficult for most people to achieve adequate sun exposure with a typical American lifestyle of indoor work and outdoor play.
Vitamin B12 is an even trickier problem. This vitamin is easy to come by from animal protein, can be difficult to absorb under many different medical conditions, and is almost entirely in the plant kingdom. Dr. Campbell contends that plants grown in vitamin B 12 rich soil can increased levels of vitamin B 12. He cites a research article in which vitamin B12 in enriched cow manure was used to fertilize spinach plants. The spinach plants indeed had a higher level of vitamin B12 but still was so much lower than naturally occurring B12 in animals. By my calculations I would be required to eat almost 15 cups of spinach grown in this special soil per day to achieve adequate levels of vitamin B 12. Ultimately I do not believe any diet that requires supplementation from the very beginning is teleologically appropriate for humans for a healthy life.
I believe one very important aspect of Dr. Campbell’s work should be highlighted. He deserves great credit for pointing out the correlation that the lower amounts of processed foods and refined sugars and carbohydrates is correlated with a healthier lifestyle. I believe that most of the beneficial effects seen in a plant based nutrition diet are achieved directly from this dietary finding. Dr. Ornish’s and Dr. Esselstyn’s work follow the same guidelines and I believe their successes are from this aspect also.