Wednesday, September 3, 2014

Yes Virginia, The Paleo Diet Was Low-Carb

[tl;dr: Clear evidence for carbohydrate level of ancestral diets.]

One of the "diet gurus" I follow and whose work I appreciate (the Prescript-Assist Probiotic was remarkable, thanks!) is Chris Kresser, formerly known as the Healthy Skeptic. I first came across Chris when he interviewed Stephan Guyenet, in Chris's first podcast back in 2010.

Recently, Laura Schoenfeld, who works with Chris as a dietician posted an article titled "Is a Low-Carb Diet Ruining Your Health?" I scanned it, tried to comment, but as commenting on Chris' site no longer seems to work for me, moved along. Then Chris posted a follow-up, "7 Things Everyone Should Know About Low-Carb Diets" because apparently, and not surprisingly, the previous post got a bit of attention.

"Last week, my staff nutritionist Laura Schoenfeld wrote a guest post for my blog called “Is a Low-Carb Diet Ruining Your Health”. Perhaps not surprisingly, it has caused quite a stir."

OK. So I read on, but stopped here:

"#1: Paleo does not equal low-carb, and very low-carb/ketogenic diets are not our “default” nutritional state, as some have claimed."

I'm just going to follow up on this one point. And not get into the rest of his post, or Laura's post. I have issues with both of them, but all those issues stem from this one fundamental misconception. So I'm going to cover just one topic: was the Paleolithic Diet low-carb?

 I'm not going to cover what people say is a paleolithic diet today, or what modern hunter-gatherers eat (there is one fundamental problem with that, but that's for later), just that one issue, because it's pretty easy to cover.

The Smithsonian Institute recently announced a massive study of Kennewick Man, an anomalous skeleton that appeared to pre-date the Indians and Eskimos who populated the Americas when my European ancestors first arrived. Initially they thought it was a modern skeleton, as it didn't have the physical attributes they associate with Indians, but one item distinguished it:

"The skull, while clearly old, did not look Native American. At first glance, Chatters thought it might belong to an early pioneer or trapper. But the teeth were cavity-free (signaling a diet low in sugar and starch) and worn down to the roots—a combination characteristic of prehistoric teeth.

(My emphasis) Yes, it turns out that being free of cavities is a hallmark of people who ate the paleolithic diet. That's zero cavities, btw, not "not many". I was told when visiting Harvard that the human relics we have from the paleolithic contain "zero" cavities, a statement which I found astounding. (More on that later.)

In fact, whether or not cavities are present (they're known as "caries" to anthropologists) is how one knows what the individual ate.

Take Ötzi, the "iceman", the famed 5,000 year-old mummy found in a glacier in Europe:

"The tooth decay is significant because it shows how starchy foods and the agriculture that created them were a part of Ötzi's regular diet. The team attributes his cavities to eating more breads and cereals."

Unlike Kennewick man, Ötzi's soft tissue was preserved, so they were able to do a DNA analysis on the contents of his gut, and, sure enough:

"According to the DNA reconstruction, the man's last meal was composed of red deer (Cervus elaphus) meat, and, possibly, cereals; this meal had been preceded by another one based on ibex (Capra ibex), different species of dicots, and cereals."

That, in a nutshell, is the difference between a paleolithic diet and a neolithic diet: cavities, and starchy foods. Starchy foods are tough to track through the archaeological records, but happily for us, cavities are easy to track.

Now it turns out that there was was one paleolithic group that ate a non-low-carb diet. I suspect these people had run out of anything better to eat, because they were subsisting on snails and acorns.

"When hunter-gatherers started adding grains and starches to their diet, it brought about the "age of cavities." At least that's what a lot of people thought. But it turns out that even before agriculture, what hunter-gatherers ate could rot their teeth.
"The evidence comes from a cave in Morocco — the Cave of the Pigeons, it's called — where ancient people lived and died between 12,000 and 15,000 years ago. These were hunters and gatherers; they didn't grow stuff. And what was astonishing to scientists who've studied the cave people was the condition of their teeth. 
""Basically, nearly everybody in the population had caries," or tooth decay, says Louise Humphrey, a paleo-anthropologist with the Natural History Museum in London."Humphrey says 94 percent of the more than 50 people from the cave she studied had serious tooth decay. "I was quite surprised by that," says Humphrey. "I haven't seen that extent of caries in other ancient populations.""

That's unique, in other words. So what did they eat?

"But apparently, these ancient people had a thing for acorns. 
""Acorns," says Humphrey, "are high in carbohydrates. They also have quite a sticky texture. So they would have adhered easily to the teeth." 
"Yes, these people did eat meat. And snails, apparently, whose shells littered the cave. But they also ate a lot acorns, judging by the debris they left behind. 
"Without toothbrushes ... without dental floss ... that diet rotted their teeth."

So these are your teeth on a non-low-carb Paleo diet. (See picture above) Not a pretty sight.One other researcher has the following insight on what caries prevalence tells us about ancient diet:

"...it is supposed that H. erectus, a hunter-gatherer, obtained approximately 50% of its calories from carbohydrates (Wrangham, 2009) and under the hypothesis of cooking (that obviously included meat and vegetables), caries should have been present much earlier in the fossil record. However, caries appears clearly much later. So, the data on oral does not support the idea of a cariogenic diet based on cooked [tuberous] vegetables from the earliest periods. Maybe, in the beginning, fire was employed only for cooking meat."

Most likely, of course, it's because they weren't eating much in the way of carbohydrates:

"Caselitz (1998) analyzed the historical evolution of caries in 518 human populations of Europe, Asia and America in a wide timeline from the Paleolithic to the present, confirming that during Paleolithic and Mesolithic periods, the hunter-gatherers had less caries and lesions progressed more slowly. Caries indices have increased gradually from Neolithic times, until they reach the high rates observed at the present.... This phenomenon, observed in North Africa, Near East, China and Europe has been attributed to the drastic change in the diet that means the introduction and spread of cereals in the entire antique world..."
("Caries Through Time: An Anthropological Overview")

Alright, but all this is some random blogger putting together a bunch of posts and drawing a conclusion that reinforces his prejudices. What good is that?

(I'll put my biases on display: I had massive cavities when I was a kid, I don't know how many. I had eight teeth pulled, including my wisdom teeth; what got me interested in the Paleo diet was when the afore-mentioned Stephan Guyenet convinced me that my tooth issues were soley the result of diet. I'd already gone largely sugar-free and had been cavity-free for about 20 years. So I was receptive to the idea that my tooth issues were the result of diet, and not genetics.)

So let's go to the expert. Dr. Daniel Lieberman is the Chairman of the Department of Human Evolutionary Biology at Harvard. He's one of the foremost anthropologists on the planet, and he recently completed his magnum opus, The Evolution of the Human Head. More to the point here, he released a newer book, The Story of the Human Body: Evolution, Health, and Disease.

In this book, he discusses a number of mismatch diseases; which are caused by a discrepancy between our environment and the environment we evolved to live in. One of the first mismatch diseases he discusses is cavities.

(Full disclosure: While Dr. Lieberman does not share all my opinions on the Paleo Diet, I need to note the following, from the Acknowledgements in that book: "Special thanks go to David Pilbeam, Carole Hooven, Alan Garber, and Tucker Goodrich , who read multiple chapters." I'm biased toward this book.)

I mentioned above a visit to Harvard. My friend John Durant had a similar visit, here's his account:

"“Notice anything?” Dr. Lieberman asked. “Look at the teeth. They’re straight. And no cavities. His wisdom teeth came in just fine. Humans, like all animals, have evolved teeth that are well suited to their natural diet. An infected tooth can easily kill you, and there were no dentists in the Paleolithic.” 
"Nearly one hundred thousand years before dentists and orthodontists, this hunter-gatherer had a strong, straight set of chompers. Skhul V challenged much of what I’d been taught about the history of human health. 
"“Now, look,” Dr. Lieberman continued, “hunter-gatherers didn’t have perfect teeth. This guy has well-worn teeth, and he’s actually missing one due to an abscess. So don’t stop going to the dentist. But wait until I show you the skulls of early farmers—a lot of them would need to get fitted for dentures.” 
"“So what’s the secret? Eat less sugar?” I asked. 
"“Well, yes, but healthy teeth depend on a variety of factors,” Dr. Lieberman explained. “First, yes, it matters what you eat. Amylase in your saliva breaks down carbohydrate into sugar in your mouth. Bacteria feed on the sugar and produce acid that wears away the enamel on teeth, giving you cavities. We’ll see what happened to the early farmers who started eating a starchier diet.” 
"To figure out what humans used to eat, teeth are a good place to start. Not only do teeth fossilize well, but they’re the first point of contact between the food we eat and our body, the first part of our internal digestive tract. And if our teeth aren’t well adapted to a particular food, it’s unlikely the rest of our digestive tract is. But whatever Skhul V was eating, his teeth seemed to be up to the challenge."

Professor Lieberman in his book is pretty succinct in his coverage of the topic of cavities:

"Unfortunately, humans have little natural defense against cavity-causing microbes other than saliva, presumably because we did not evolve to eat copious quantities of starchy, sugary foods. Cavities occur at low frequencies in apes, they are rare among hunter-gatherers, they started to become rampant following the origin of agriculture, and they spiked in the nineteenth and twentieth centuries. Today cavities afflict nearly 2.5 billion people worldwide." 
"...if we really wanted to prevent them, we would have to reduce our consumption of sugar and starch drastically. However, ever since farming, most of the world’s population has been dependent on cereals and grains for most of their calories, making a truly cavity-preventing diet impossible for all but a few. In effect, cavities are the price we pay for cheap calories. Like most parents, I let my daughter eat cavity-causing foods, encouraged her to brush her teeth, and sent her to the dentist, knowing full well that she’d probably get a few cavities. I hope she forgives me."

To me, this seems to be a pretty clear indication that the Paleolithic diet as actually eaten in the Paleolithic period did not include a large amount of carbohydrates; or, if it did, they were eaten infrequently enough so that the population of bacteria required to rot your teeth did not have the opportunity to arise in your mouth.

Keep in mind, other than the acorn-eaters, the Paleolithic cavity count was around zero.

I'd be very interested to hear another explanation for this particular phenomena, but for me, it's pretty cut-and-dried. Our Paleolithic ancestors ate fewer carbohydrates than any other group currently existing, or there was some other unknown phenomena that protected their teeth.

So what's the right amount of carbohydrates to eat on a Paleo diet? The amount that means you won't need to brush your teeth, ever. If you don't get any cavities, then you're eating the right amount. If you're getting cavities, you're eating too much. Based on the evidence above, I'm going to guess that's a low number. So why not err on the safe side, as there's no good evidence not to?

We got by for quite a long time on that diet, and became human while eating it.

"On the other hand, there are some foods that inhibit the formation of caries. Diets rich in meat lead to low caries frequencies due to the fatty acids’ antibacterial power and their capacity to reduce the adherence of plaque on dental surfaces. The intake of dairy products and fish (foods rich in calcium and casein that can increase urea concentration) modifies pH values and the quantity of salivary production, inhibiting the formation of dental plaque. Finally, a food rich in polyphenols (such as cacao, coffee and tea) inhibits the bacterial metabolism and stimulates the salivary secretion representing, thus, another mechanism of caries prevention (Bowen, 1994; Touger-Decker & Loveren, 2003).

(From the Caries Overview.)

P.S. I see from the comments below that I never did get around to covering this point:

" I'm not going to cover what people say is a paleolithic diet today, or what modern hunter-gatherers eat (there is one fundamental problem with that, but that's for later)..."

The problem with using modern hunter-gatherers to infer what our Paleolithic ancestors ate is that there environments were totally different.  Paleolithic man was the apex predator on the planet, dominating the premier hunting grounds and sending many species  into extinction through over-hunting.  He traveled the world in search of game.

Modern hunter-gatherers live in fringe, largely less-productive environments.  They're getting by on what's left, in other words.  The primary environments for ruminants, our preferred food, has largely been given over to agriculture.  See the decline of the bison in the United States.  HGs eat a lot of tubers but mostly talk about eating meat, because that's what they really want, but can't get.  Tubers are a "fall-back" food: it's what you eat when your primary foodstuff is not available.