Fundamentally, I am a proponent of the Paleolithic diet. However, much depends on the specifics of the Paleo diet in question. The designation seems to be somewhat open to interpretation -- and thus the dietary devilry may reside in the details.
That, in essence, is the punch line for this piece -- and I provide it right away as a bow to a recent correspondent who reminded me that busy readers want the take away, right away. I do, however, hope you hang in there for the rest. Assuming so, let's start this tale at the beginning.
In June of this year, U.S. News & World Report published a ranking of diets for weight loss and health promotion. They circulated the contestants to a panel of 22 judges, all with relevant expertise, who scored each diet in multiple categories. Scores were tallied and winners declared. The overall winner for weight loss was Weight Watchers. The Paleo diet fared rather badly.
Shortly after the rankings were published, I was contacted by ABC News and asked to comment on why the Paleo diet had been scored so poorly and what I thought about it. My first comment was that I was one of the 22 judges, and that I had not scored the Paleo diet poorly. I went on to say that I considered a true "Paleo diet" -- with an emphasis on eating foods direct from nature and more plants than animals -- a good idea. I also noted that the name could mask a host of ills, such as a diet of hamburgers, hot dogs and bacon.
Apparently, the gist of my comments as quoted by ABC News suggested I was a general critic of the Paleo diet, and also conveyed my impression that our ancestors actually ate more plants than animals.
This resulted in correspondence from Loren Cordain, a Professor in the Department of Health and Exercise Science at Colorado State University, who has published extensively on our Stone Age diet and its implications. Prof. Cordain's note was very civil, but nonetheless a chastisement of my excessive emphasis on gathering over hunting, with a cc to a veritable who's who in paleoanthropology.
I explained to Prof. Cordain, and the others listening in, that I am a proponent of our true ancestral diet, while dubious about its many modern variants. The notion -- expressed in much of Prof. Cordain's own work -- that our ancestors ate a lot of meat, has invited modern carnivores to run up their "Paleo diet" banner and claim to be eating under it.
But they are not, because modern meat is not Stone Age meat. There were no wild corned beef, salamis or pastramis in the Stone Age, so processed meat is certainly off the Paleo diet menu. There were no grain-fed cattle; no pigs fed slop; and no domesticated feed animals raised without demands on their muscles, either.
The flesh of animals our ancestors ate was generally quite lean, often with fat content around 10 percent of calories or lower. That fat was far more unsaturated than the fat in most modern meats as well and even provided some omega-3.
Prof. Cordain noted that the flesh of grass-fed cattle approximates the Paleo experience, albeit imperfectly. Game does so even better. I concur -- but how much of this is there in the modern food supply? In my experience, many people who use the Paleo diet as justification for carnivorous preferences simply eat more of the kind of meat they tend to find. And generally, they are not finding antelope.
The issue of animal vs. plant foods remained, however, and I was fully prepared to simply respond with "mea culpa" (I know when I'm out of my weight class!), when Dr. S. Boyd Eaton of Emory University was gracious enough to contribute his views. While many papers examining the proportion of hunting to gathering are based on averages among modern-day hunter gatherers in diverse locales, Dr. Eaton has focused on African populations thought to most closely approximate the original human experience. Dr. Eaton's work suggests a plant:animal calorie ratio of 1:1.
Which, in essence, suggests that any apparent differences I had with Prof. Cordain were a bit about semantics (volume vs. calories), and a bit about which data to emphasize. Since plants tend to be energy-dilute and animals energy-dense, to get a 1:1 calorie ratio means a much greater than 1:1 ratio of plant food volume to animal food volume. It means quite a lot of gathering along with the hunting. Mostly plants, in other words, is not demonstrably wrong. Seemingly in the company of Dr. Eaton, I think my original assertion defensible.
Of course, the true beginning of a story about our Stone Age diet resides not with U.S. News & World Report, but in the Stone Age. The Paleolithic era, spanning our use of rough stone implements, extends some 4 million years into the past.
We may reasonably limit ourselves to the latter half of that span and focus on the emergence of our Homo erectus forebears, thought to be the first highly effective human hunters, roughly 2 million years ago. Our own species, sapiens, arose roughly 300,000 years ago and our particular subspecies, sapiens sapiens, roughly 30,000 years ago. Agriculture was not part of the human experience until roughly 12,000 years ago -- and once it was, nothing was ever the same. But that's a story for another time.
The Stone Age thus provided several thousand millennia to shape the adaptations of our genus, and several hundred to shape those of our species. We carry the genes of the well-adapted, because ancestors not well-suited to survive, reach adulthood and make babies ... make very poor ancestors. Like all modern creatures, we are the posterity of pre-modern creatures who "had the stuff," and paid it forward.
Among the stuff that mattered was the capacity to extract all necessary fuel from available foods. This is very easy to understand at the extremes: a person who required for their survival a nutrient not found on this planet, would not survive on this planet. A person who could not tolerate a nutrient essential for survival, such as water, similarly would not survive. While this is so obvious as to be trivial, it conceals a subtlety: food came first, physiology came after. There were plants before there were creatures that could survive by eating plants. There was water before there were creatures that needed to drink water.
And the same extends to every detail of dietary intake. We are adapted to survive on protein, carbohydrate and fat because those are the three kinds of macronutrients this planet provides. We "need" iron and calcium and essential amino acids and potassium and vitamin C -- because the food supply available to us on this planet provides them. If it did not, we could not possibly need them and be here to talk about it. Other creatures that needed what the planet did provide would be here in our place.
It just stands to reason that the diet that shaped our physiology in the first place would tell us something about the diet for which that physiology is best suited now. If you find that hard to swallow, consider how we decide what to feed animals in a zoo. To my knowledge, no clinical trials are involved in which the lions are tried on a diet of hay and the koalas on a diet of mackerel. Instead, the animals are all given food approximating what they were eating in the wild -- their native diet. If this is relevant to every creature on the planet, how likely is it that it would be irrelevant to us?
This, then, is the basic argument for the "Paleo diet." But there is more to consider. Throughout much of the Stone Age, mean human life expectancy was all of about 20 years and the life span extended only to about 40. While it makes sense that our native diet is apt to be good for us, we cannot conclude that a diet best suited to a two- to four-decade life is just as good for an eight-decade life.
Our Stone Age ancestors had a high caloric throughput, meaning lots of calories both out and in every day, due to the high energy demands of Stone Age survival. Perhaps consuming 4,000 or so calories a day -- and burning them all -- should be required before the "Paleo diet" label truly pertains.
Dr. Eaton among others suggests that our Paleolithic ancestors consumed as much as 100 grams of fiber daily, from a variety of plant foods eaten in large enough quantities to fuel that high energy demand. If 100 grams of fiber a day were required to defend a Paleo diet claim, there would be very few signed up.
In reality, virtually no one today practices anything close to a true Stone Age diet and no one at all practices such a diet perfectly. When was the last time you saw a mammoth?
When the Paleo diet label is used to justify a diet of sausages and bacon cheeseburgers, the concept has wandered well off the reservation. When used as guidance away from processed foods and toward a diet based on a variety of plants, nuts, seeds, eggs, fish and lean meats (preferably wild game), it is eminently reasonable, and no doubt a vast improvement, over the typical American diet. Stone Agers did a lot more running than we do and most certainly did not run on Dunkin'!
We don't know that even a well-practiced Paleo diet is the "best" choice for health, as compared to a Mediterranean diet, a traditional Asian diet, a mostly-plant diet, or a well-balanced vegan diet. We do know that a population of some 7 billion people cannot eat as much meat as a population in the millions did, without doing the irreparable harm to the planet that is already far advanced.
That our native diet is relevant to our health seems little less than self-evident. That we can't get back to the Stone Age from here is equally so. Exactly how we apply lessons from the past to our current dietary practices will decide whether effects on our future health, and that of our planet, are as hoped- or otherwise. So the details matter; let's chew on them carefully.
David Katz, MD