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The Protein Debate - Loren Cordain, PhD v. T. Colin Campbell, PhD

Protein plays a litany of roles in living systems: structural elements, peptide hormones, cell recognition, antibodies… the list is staggering and continues to grow as our understanding of biology expands. What, however, is the role of dietary protein in health and disease in humans? Is the source, type and quantity intimately and directly tied to optimal physical development and continued wellbeing? Is it causative or preventative of disease? How do we know, and how can we know?

One would think this question should be straightforward and easily answered; as you will soon see the question is anything but simple! In the pages that follow, two scientists at the top of their respective fields--Dr. T. Colin Campbell, Professor of Nutritional Biochemistry at Cornell University, author of The China Study and Dr. Loren Cordain Professor, Department of Health & Exercise Science, Colorado State University, author of The Paleo Diet—make their competing cases for the role of dietary protein in health and disease.

Click on the PDF attachment below to read the debate.

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Excellent post, Richard. A few comments on Dr. Cordain's article discussing epidemiological evidence of the link between diet and disease:

One possible explanation for the contradictory results of observational epidemiological studies on the association between diet and disease is due to exposure misclassification of one's dietary intake. That is (as stated in the review article attached below), classification of dietary intake is based either on short-duration (i.e., 24-hour) assessments by dietitians or questionnaires on long-term history of dietary intake.

Both are limited in what they can provide. The former provides a more accurate quantification of dietary intake (i.e., the amount of protein, carbs, and fat consumed), but is not representative of usual, long-term trends of an individual's dietary intake. Conversely, history questionnaires provide information regarding an individual's usual trends in dietary intake, but this method of data collection suffers from an inability to accurately quantify the amount of fats, proteins, and carbs ingested and is also subject to recall bias (i.e., the further in the past one is asked about their diet, the less likely they are to recall it correctly).

So, in reading articles about the association between diet and disease, take into account how the study assessed dietary intake in addition to the population studied. For instance, if the study was only among diabetics, the results can only be applied to those who are diabetic. Other study aspects to take into consideration include:

1) Sample size (the smaller the sample size, the less statistically accurate the results),

2) Study design (i.e., does the study assess past exposures [known as a retrospective study], follow people forward in time [known as a prospective study], or is the study directly involved in the participants' exposure [i.e., clinical trial]),

3) How the researchers defined exposure (e.g., diet) and outcome (e.g., heart disease).

Remember, one study cannot prove causation. Every study has its weaknesses that limit its interpretation to the general population. Before making a choice as to whether to alter your diet, review the collection of research and not just one study. This actually provides a segue into my take on health reporting in newspapers, magazines, and blogs, but I shall refrain from stepping onto that soapbox.
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