I have read through the debate twice, and I have also read various reviews and comments that have been posted on two different blogs. And from what I have seen, the consensus seems to be that Dr. Cordain prevailed over Dr. Campbell. One thing is for sure: they could not have come up with two more diametrically opposed advocates.
Technically, Dr. Cordain may indeed have won the debate because he did put a lot more effort into it. He provided numerous scientific references to back-up his claims, whereas Dr. Campbell didn't provide any- except for a few in his brief rebuttal. You might say that Dr. Cordain offered more "meat," both in his diet and his presentation. However, even though he didn't make his case as well, in my opinion, Dr. Campbell's position is closer to the truth. And I'll tell you why.
Despite his greater eloquence and verbosity, Dr. Cordain's case really came down to just one argument: that modern humans are descendants of hominoids who ate high-protein, high-meat diets for a very long time, eons, and they "evolved" on such a diet. Therefore, our "genome" (referring to our total genetic nature) demands that we follow such a diet because we are clearly "adapted" to it. He alleges that such a diet is deeply ingrained, mandated, and stamped in our very genes.
I put some of those words in quotes because they are all derived from modern evolutionary theory. But I think that it's wrong. The idea that random genetic mutations underwent "natural selection" to make us who and what we are is nonsense. Here is a link to my article about it: http://www.1to1vitamins.com/news/2007/artl6239.html
Since Cordain's whole case is based on Evolutionary Theory, if Evolutionary Theory is wrong, then his whole argument falls apart, which I think it does. In a way, he's like a guy hopping around on one foot. All I have to do is sweep that one leg out from under him, and he goes tumbling down. He's got nothing else to stand on.
Why, may I ask, should the whole science of human dietetics be based on just ONE consideration, namely, what did our ancestors eat? Granted, it's an interesting question, and I think it is an important question. But it is not the only consideration. For example, it pales in comparison to doing clinical research studies and epidemiological studies of modern humans, feeding them different diets and then observing and comparing their outcomes and results. That is far more valuable and important and crucial than just being dogmatic about following in the footsteps of our remote ancestors. But to Cordain and his followers, paying homage to the Caveman and trying to duplicate his way of life as much as possible has become both a religion and an obsession.
Whenever I start talking about the quest for the optimal diet, the first thing that comes to mind is the realization that the most proven technique and method of life extension is caloric restriction. Imagine, with all the knowledge we have about vitamins, minerals, hormones, antioxidants etc., it turns out that simply controlling the amount of food eaten is the most certain way to stem disease and prolong life. Experimentally, it has worked with animals large and small, and there is every reason to believe that it works the same way with humans.
So, what does it mean to restrict calories? It means to restrict proteins, fats, and carbohydrates. Those are the only things that have calories. In a sense, we say "calories" just because it's less work than writing out "proteins, fats, and carbohydrates." But which of the three should be most restricted? Obviously, there is debate about that, but I see no reason to be biased one way or another. Why do we have to particularly demonize any of one of them? I say restrict all of them. Try to determine how much of each is really, truly needed and then set the restriction bar a little above that. That makes sense to me.
Let me stress that I am not an advocate of extreme caloric restriction. I do not think people should make themselves downright skinny and wasted in an attempt to prolong their lives. But I do think the principle is sound, and that applied in moderation (which is maintaining an attractive, healthy leanness), it has a lot to offer.
So how much protein is needed? Well, let's look at what protein is used for by the body. Basically, it comes down to two things: structure and function. You need protein to maintain structures, including muscles, bones, tendons, ligaments, organs, etc. And then on the functional side, you need protein to make enzymes, hormones, neurotransmitters, immunoglobulins, and other functional components. How much does that all add up to? Well, Dr. Campbell proposed a number that is actually quite widely agreed upon in Science: .8 grams of protein per kilogram of body weight. Dr. Cordain never offered any formidable objection to that figure except to imply that it referred to a minimal amount- enough to barely get by. But as Dr. Campbell explained in his rebuttal, that is really not true. The figure includes a safety factor to cover the few people who require more for various individual reasons. Dr. Cordain never offered a technical, quantitative reason why that figure should be considered insufficient, other than that it vied with the "evolutionary model."
Let's take me as an example. I am 5'6" and weigh 137 pounds, which is 62 kilos. That works out to a dietary protein need, according not only to Campbell but to most nutritional scientists, of about 50 grams of protein a day. I probably get closer to 60 or 70, and that's eating almost entirely plant foods and without eating any meat at all. And on that diet, I am maintaining my weight and my strength and my health. I'm not heavily-muscled, but I am rather toned and fit and athletic, especially for a man my age. At least, I think I am. I don't go to the gym, but I do have some exercise equipment that I use at home, plus I bicycle regularly and swim in the summer. At age 55, my goal is to preserve the muscles that I have, that is, to keep them from dwindling. If I do that, say over the next ten years, I will be doing better than 98 percent of people, because most people, the vast majority, male and female alike, lose quite a lot of muscle over that decade- no matter how much protein they eat. And so far, I seem to be managing OK. I don't seem to have lost any muscle size or strength between the ages of 45 and 55, which is pretty good in itself. And I have every hope and expectation of doing the same between the ages of 55 and 65. But my plan does not involve loading up on animal protein. Why should I? I didn't do that the last ten years, and I maintained my strength and fitness. Remember, I'm not trying to make my muscles grow; I'm only trying to maintain what I have. I'm not saying it's impossible to grow new muscle in your 50s and 60s, but it's darn hard, and I'm not sure it's worth trying. The things I might do to accomplish that might cause me stress and strain in various ways, and since I'm content with my overall size and strength and proportions, I'm inclined to leave well enough alone and just try to maintain. So that's my plan. In fact, the only way I could possibly gain new muscle is if I started doing very heavy exercise- lifting heavy weights. But I'm not going to do that because it's not going to make me any healthier overall, and I could easily get hurt. Do you think I want to spend my hard-earned money supporting physical therapists, chiropractors, and orthopedists? I assure you I don't. But what would happen if I kept up the same level of exercise that I do now, the same workload on my muscles, and just increased my consumption of dietary protein? I'll tell you what would happen: nothing.
Muscles don't respond and grow just because you eat more protein. If they did, then all the people (men and women alike) who go on high-protein diets to lose weight would get more muscular as they did it. But of course they don't. So what happens to the extra protein? It gets broken down. The body deaminizes the excess amino acids, breaking off the nitrogen radical which basically becomes ammonia. Then, the liver wraps up the ammonia radicals into a larger molecule known as urea (which is easier to handle; it's not irritating the way ammonia is), which is then excreted by the kidneys. This amounts to extra work for both the liver and the kidneys. But it has to be done so that the body can process the extra protein as a fuel, either for burning or for storing as fat. (Yes, the body can convert protein into both carbohydrate and fat.) But when it comes to my need for fuel, I would rather rely on carbohydrates or even fats because both carbohydrates and fats burn all the way down to carbon dioxide and water. And nothing else. That's clean fuel. Why should I try to burn proteins when the nitrogen radical won't burn? Think of it like a log that you throw on the fire to create heat (which you want) but which also generates a bunch of black smoke (which you don't want).
But getting back to Dr. Cordain's arguments again, relying on the "evolutionary model" to evaluate all things biological is both presumptuous and, in my opinion, wrong. It occurs to me that human ancestors ate the way they did "way back when" not necessarily because of some evolutionary mandate, but because there was an Ice Age going on. Granted, under primitive Ice Age conditions, you either feed heavily on meat, or most likely, you die. But now that things have warmed up and the ice is mostly melted, we don't have to do that any more. And no, our genes are not going to scream bloody murder if we don't.
Dr. Cordain seems to think that only when we eat so much protein that we saturate our liver with unconverted ammonia do we get into trouble. Sure, that is a deadly situation, but don't you think there are lesser and more subtle degrees of harm from excess protein? And regarding the kidneys, he admits that people whose kidneys are already impaired suffer from high-protein diets, but for those whose kidneys are in the normal range, he assumes that they "adapt" to the greater workload of a high-protein diet. Even if that's true, and I'm not sure it is, give me one good reason why we should give our kidneys the extra work? Don't think of it as a beneficial thing like physical exercise. It's not like that at all. I know from my own clinical experience that people who eat high-protein diets have higher levels of blood urea nitrogen (BUN), and I don't see that as a good thing. He can laugh it off if he wants to, but I do not. I would add (and he agrees) that high-protein, meat-based diets result in higher purine intake, which is tied to the formation of uric acid. However, he tries to argue that somehow that's a good thing, and that high-purine diets actually lead to lower uric acid. But his argument is very weak. He makes some startling citations, true, but trust me, it goes against the bulk of the scientific evidence concerning gout.
Regarding bone health, Dr. Cordain admits that high-protein diets result in increased urinary loss of calcium. But he argues that it doesn't matter because at the same time, intestinal absorption of calcium increases. But that doesn't change the fact that there is a strong epidemiological correlation between high-meat diets and osteoporosis. I agree, as he points out, that there can be "confounding variables." But even when researchers try their best to account for those confounding variables, the association still remains. Besides, even if it is true that high-protein diets cause increased calcium absorption, we should wonder why. It's well known that the body cranks up the efficiency of calcium absorption precisely when it is under calcium duress. Perhaps that is what is going on.
I will close by making one last point, and I'm surprised that Dr. Campbell didn't make it. Look at the comparative analysis of mammalian milks. Meat-eating, high-protein feeders, like lions and tigers, and for that matter even dogs and cats, have much higher amounts of protein in their milks than do cows or sheep or people. In fact, do you know which mammal has the lowest protein content in its milk of all? Yes, it is the human being. Human breast milk has a protein content of only about 1 percent, whereas dog milk has 7.5 percent protein, and cat milk has 10.6 percent protein. In fact, I have seen human breast milk listed to be as low as .8 of 1 percent protein. Yet, on an exclusive diet of low-protein breast milk, a human baby can double its birth weight in a matter of months. Let's see you talk your way around that one, Dr. Cordain.