Protein?

It's a prevailing topic in most strength and conditioning circles, a great concern to athletes in general, and I'm sure the rest of the populace has thought about it at one time or another: How much protein do I need? The answer is anything but simple, and I wouldn't dare suggest that I'm qualified to give out that kind of advice. What I do offer is a synopsis of a debate that I recently read from The Performance Menu on this very topic:


THE PROTEIN DEBATE
Loren Cordain, PhD & 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, Jacob Gould Schurman Professor Emeritus 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.

Full text article available for free download


Warning!! Spoilers!! Only read on if you have read the article (or if you don't want to read the article and just want to know what I think about it)

In my opinion, Cordain owned Campbell in this debate. Campbell's arguments were weak and unsubstantiated (he provided absolutely no references), and his protein recommendations were based on the assumption that the only physiological significance of protein is to replenish excreted nitrogen. He attacked animal protein as the cause of numerous diseases, without providing a shred of evidence as to why that's so. Cordain's discussion about the evolutionary basis for the therapeutic effects of high protein diets was informative and well written. While I don't agree with everything that Cordain has to say, mostly surrounding saturated fat (another great topic for a future post), I find his insights compelling, and he always backs up whatever he has to say with numerous references that are easily accessible. A few highlights from the debate:

"...it should be noted that there is a physiological limit to the amount of protein that can be ingested before it becomes toxic. A byproduct of dietary protein metabolism is nitrogen, which in turn is converted into urea by the liver and then excreted by the kidneys into the urine. The upper limit of protein ingestion is determined by the liver’s ability to synthesize urea. When nitrogen intake from dietary protein exceeds the ability of the liver to synthesize urea, excessive nitrogen (as ammonia) spills into the bloodstream causing hyperammonemia and toxicity. Additionally excess amino acids from the metabolism of high amounts of dietary protein may become toxic by entering the circulation causing hyperaminoacidemia."

Sounds like a pretty good determinant for how much protein is too much, doesn't it? Dr. Campbell didn't think so:

"If this is an inference that all could be well until this limit is reached, it is grossly misleading."

I don't think that Cordain ever meant to infer that all is well up to this limit of protein consumption. In fact, he goes on to say that this level of protein consumption is unrealistic to expect in all but the most drastic situations, such as when humans were forced to rely upon the fat depleted, lean meat of wild animals in times of harsh weather conditions and resource scarcity. His protein recommendations are genetically based, pulling from isotopic fossil and ethnographic evidence, and he concludes that:

"The evolutionary evidence indicates that so called “high protein diets” (20 – 30 % total energy) and “very high protein diets” (30- 40 % total energy) actually represent the norm which conditioned the present day human genome over more than 2 million years of evolutionary experience. The evolutionary template would predict that human health and well being will suffer when dietary intakes fall outside this range... There is now a large body of experimental evidence increasingly demonstrating that a higher intake of lean animal protein reduces the risk for cardiovascular disease, hypertension, dyslipidemia, obesity, insulin resistance, and osteoporosis while not impairing kidney function."

And now, Campbell's recommendations:

"Probably the simplest method of determining recommended intakes, at least conceptually, has been the N balance study. An experimental determination is made of how much protein, analyzed according to its N content, must be consumed in order to compensate for the average daily amount of N lost from the body. After adjusting for the 16% N content of protein and after adjusting upward the experimental mean by two standard deviations to include the needs of about 98% of the larger population, this gives an ‘allowance’, or recommendation, of 0.8 gm of protein to be consumed per day per kg of body weight, for both sexes... The question, then, should not be how much protein is needed but how much protein in excess of the 10% dietary level can be safely consumed."

That's it. Protein is nothing but a nitrogen vehicle, and extreme caution should be used when handling it. Cordain's response:

"nitrogen balance studies have been extensively used to predict the minimal human protein requirements. Because all protein contains 16.6% nitrogen, then the measurement of nitrogen serves as a proxy for protein. Colin’s argument is that optimal health occurs when we are in zero nitrogen balance (e.g. when our daily nitrogen intake = daily nitrogen excretion), and that excessive protein intake and hence negative nitrogen balance (nitrogen intake <>minimal protein requirements provide no information about optimal protein requirements."

And this is where I think that Cordain has hit the nail on the head. Where as Campbell seeks to demonize protein (particularly animal-based) and claim that it is the cause of numerous diseases when consumed in excess (which he provides zero evidence for), Cordain attempts to establish parameters for optimal protein requirements, based on the success of peoples with no influences over what to eat except for what was available to them and what their DNA told them was right (WARNING, oversimplification).

I have to admit, I consider myself an evolutionary biologist. Although I have no formal education on the topic (I have read some really good books on the topic however), it's just what makes the most sense to me. Because of this, my opinions are in no way an objective analysis of this debate.