I’ve been meaning to write a post defending the evolutionary logic of the so-called “Paleo diet” for awhile, but it wasn’t until I read Marlene Zuk’s article in the Chronicle “Misguided Nostalgia for Our Paleo Past” that I really felt motivated to do so. Normally my approach to engaging with another thinker is to write in essay format, but my problems with Zuk’s article are numerous enough to warrant a point-by-point reply. Here goes!

These scientists are looking for signs of changes in the genes that allow us to consume dairy products past the age of weaning, when all other mammals lose the ability to digest lactose, the sugar present in milk. [emphasis added]

Right away Zuk trades off a sneaky ambiguity in her use of “us”. The way she phrases it suggests she means “all humans”, when in fact the majority of humans (especially in Asiatic populations) are lactase-nonpersistent, which is defined as being unable to completely digest lactose. Wikipedia links to a 2003 paper in Annual Review of Genetics that starts off saying “In most mammals…lactase activity declines after the weaning phase, and this is also the case in the majority of humans throughout the world who are described as lactase nonpersistent.” So if the science says that only 25% of adult humans can fully digest milk, it’s clearly misleading to talk about “our” ability to consume dairy when by “our” she could only mean a minority of humans. And if this is the case, is it so unreasonable to use “evolutionary logic” to guide dietary decision making? You don’t need to know about evolution to not drink milk if you are lactose intolerant but as the phrase goes, nothing in biology (or nutrition) makes sense except in the light of evolution.

But in some groups of humans, particularly those from Northern Europe and parts of Africa, lactase—the enzyme that breaks down lactose—lingers throughout life, allowing them to take advantage of a previously unusable food source.

Ok, so she acknowledges later that it’s “some groups”. But why be so misleading in the first place?

The details of their experiences, of course, are lost forever. But the signature of what they were able to eat and drink, and how their diet differed from that of their—our—ancestors, is forever recorded in their DNA.

And it’s also recorded in archaeological sites and food dumps. Archaeologists can learn a lot about dietary habits of our ancient ancestors based on the remains of food in the garbage.

Other than simple curiosity about our ancestors, why do we care whether an adult from 4,000 years ago could drink milk without getting a stomachache? The answer is that these samples are revolutionizing our ideas about the speed at which our evolution has occurred, and this knowledge, in turn, has made us question the idea that we are stuck with ancient genes, and ancient bodies, in a modern environment. We can use this ancient DNA to show that we are not shackled by it.

There is a crucial difference between the notion that we are stuck with ancient bodies and the notion that we are highly constrained by our ancient bodies. I don’t know of any serious Paleo enthusiast who thinks in these absolutist terms of being “shackled” to the past. Zuk has a journalistic tendency to only engage with extreme caricatures of the position she’s attacking. We could distinguish between strong and weak versions of the Paleo hypothesis, but Zuk only attacks the absurd idea that evolution has “stopped”. But surely it’s possible to accept the idea both that evolution can in some cases work faster than was once thought and there are some things that we should minimize in our diets (like refined sugar). There is nothing incompatible with thinking that humans are adapting to some aspects of the modern environment but that the adaption isn’t complete enough to warrant throwing caution to the wind and treating, say, a fillet of salmon as nutritionally equivalent to chocolate chip cookies because, hey, perhaps we will deventually develop “cookie tolerance”. It happened with milk right? So why not cookies? Or Bob Evans’ Stacked & Stuffed Strawberry Banana Cream Hotcakes?

The absurdity of thinking humans will be adapting to Bob Evan’s Hotcakes anytime soon is highlighted by the obvious empirical observation that people with diets featuring heavily in such foods suffer from more health problems such as obesity, type-II diabetes, metabolic syndrome, cardiovascular disease, etc. But wait you say! What if Hotcake eaters out-breed the health nuts? Wouldn’t that provide pressure to adapt to Bob Evan’s Hotcakes? But it’s possible they would be reproductively successful in spite of their bad diet and not because of it.

That assumption makes us feel that humans, who have gone from savanna to asphalt in a mere few thousand years, must be caught out by the pace of modern life, when we’d be much better suited to something more familiar in our history. We’re fat and unfit, we have high blood pressure, and we suffer from ailments that we suspect our ancestors never worried about, like post-traumatic-stress disorder and AIDS.

Zuk conveniently forgets to mention the primary “diseases of affluence” such as type 2 diabetes, metabolic syndrome, asthma, coronary heart disease, cerebrovascular disease (stroke), peripheral vascular disease, cancer, alcoholism, gout, and some types of allergies. Gary Taubes has brilliantly chronicled the history of hunter-gatherer peoples being introduced to the “Western diet” of cheap processed flour and sugar in bulk. This shift in diet is inevitably correlated with rises in the diseases of affluence. A study even came out recently saying “Mesolithic hunter-gatherers living on a meat-dominated, grain-free diet had much healthier mouths that we have today, with almost no cavities and gum disease-associated bacteria, a genetic study of ancient dental plaque has revealed.” If you look at the dental health of the Royal Families’ of the ancient South/Central American empires, they inevitably had rotten teeth from being able to afford to eat sweet corn snacks all day. Guess what product makes up 90% of the food in the supermarket aisles? Corn!

That’s why the prescription for good health may be as simple as asking, “What would a cave woman do?”

This is a laughably simplistic caricature of how Paleo people approach their diet. Sure, like pretty much any human activity, there will always be people who get excited about lifestyle change and take it to the extremes, but the Paleo diet isn’t all or nothing. As others have said, it’s ideally a template to build a diet around not a sacred covenant to never eat sugar or carbs again. It’s a heuristic not a holy grail. If all you did was minimize the foods Paleo people discourage rather than never ever eat them you would do wonders for your health. If all you do is stop drinking sugary beverages and try to minimize your consumption of sweets, that would still be a net positive.

“Our bodies evolved over hundreds of thousands of years, and they’re perfectly suited to the life we led for 99 percent of that time living in small hunting and gathering bands,” writes a commenter on the New York Times health blog Well.

You know you are dealing with a strawman when you have to get your opposition quotes from the comment sections of health blogs. Why not quote from, you know, actual scientists who have written books on the Paleo and low-carb diet?

Some of our nostalgia for a simpler past is just the same old amnesia that every generation has about the good old days.

Instead of engaging with the scientific evidence piling up against the heavy consumption of sugar and refined carbs, Zuk proceeds to psychologize her opponents. This often happens in debates that are based more on ideology than science. Unfortunately, Zuk’s article is a fluff-piece heavy on ideology but light on science, which is ironic as Zuk herself is a scientist.

Now we worry about our kids as “digital natives,” who grow up surrounded by electronics and can’t settle their brains sufficiently to concentrate on walking the dog without simultaneously texting and listening to their iPods.

This article started has an attempt to engage with people who promote a Paleo diet but now she is also lumping these people in with those who worry about technology in general. This is a poor argumentative strategy because obviously providing a critique of Luddism is irrelevant to concerns about nutrition and health.

To think of ourselves as misfits in our own time and of our own making flatly contradicts what we now understand about the way evolution works.

This is another conflation between the dietary lifestyle of Paleo versus the broader Luddite lifestyle of commenters on health blogs.

Given this whiplash-inducing rate of recent change, it’s reasonable to conclude that we aren’t suited to our modern lives, and that our health, our family lives, and perhaps our sanity would all be improved if we could live the way early humans did. [emphasis added]

This is another extreme caricature. Paleo is the idea that our lives would be improved if we ate like early humans, not lived. Obviously these are two different things. One is a complete lifestyle reversion based on fantasy, the other is a sensible approach to building dietary templates.

Newspaper articles, morning TV, dozens of books, and self-help advocates promoting slow-food or no-cook diets, barefoot running, sleeping with our infants, and other measures large and small claim that it would be more natural, and healthier, to live more like our ancestors. [emphasis added]

I just had to comment: Zuk is woefully out-of-step with contemporary scientific research on the emotional benefits of co-sleeping. Zuk should read The Science of Parenting and get her facts straight.

We cannot assume that evolution has stopped for humans, or that it can take place only ploddingly, with tiny steps over hundreds of thousands of years. In just the last few years we have added the ability to function at high altitudes and resistance to malaria to the list of rapidly evolved human characteristics, and the stage is set for many more.

Nothing Zuk says here is incompatible with the sensible thought that it’s bad for your health to eat too much sugar, heavily processed enriched flour products, or high-fructose corn syrup. Zuk seems to suggest that because the “stage is set” for future adaptations, we can be justified in eating whatever we want because, hey, maybe it will one day be good for us! This would of course be an absurd way to make dietary decisions.

The paleofantasy is a fantasy in part because it supposes that we humans, or at least our protohuman forebears, were at some point perfectly adapted to our environments.

I don’t know any serious thinker who understands evolution who thinks we were at some point “perfectly” adapted. Perhaps commenters on blogs might think such things, but should Zuk pat herself on the back for successful rebutting an incredibly naive and simplistic hypothesis held only by laypersons?

These often conflicting needs mean automatic trade-offs in every system, so that each may be good enough but is rarely if ever perfect.

It’s laughable that Zuk is lecturing Paleo folks about the notion of “trade-offs” because the whole logic of Paleo is based on the idea that there is a trade-off for having a undiscriminating sweet-tooth that cannot stop once started versus a “smarter” sweet-tooth that is more computationally costly but would use more strategic planning in consuming sugar.

Did we really spend hundreds of thousands of years in stasis, perfectly adapted to our environments?

Not surprised to see another strawman.

For that matter, it might be nice to be unicellular: After all, cancer arises because our differentiated tissues run amok. Single cells don’t get cancer.

It must be convenient to have the luxury of only attacking the most absurd versions of your opponents ideas.

How do we know what we do about the rate at which evolution occurs? If lactose tolerance can become established in a population over just a handful of generations, what about an ability to digest and thrive on refined grains, the bugaboo of the paleo diet?

This is a specious line of reasoning. First of all, lactose tolerance has yet to be established in something like 75% of the human population. Second of all, we can determine the proximal chain of biological causes that explains why eating milk if you are lactose intolerant has an overall negative health effect. And it just so happens that it’s fairly easy to determine a proximal chain of causes that links excessive grain consumption with increased blood glucose levels, which has been scientifically linked to a range of health problems such as arterial inflammation, insulin resistance, and metabolic syndrome. If we followed Zuk’s logic, we should tell people who are lactose intolerance that it’s ok to eat milk because maybe a mutation will happen in the future that will make it healthier. If we already know the proximal mechanisms for why eating grains is bad, then we should continue avoiding them until something in the causal chain changes. But right now the evidence suggests that spiking your glucose levels with excessive grain consumption is not healthy and speculation about mutations in the future is irrelevant. Until I see concrete evidence that the proximal mechanisms have changed enough to nullify all these known effects, I will continue to restrict my intake of refined carbs the best I can.



Ok, that’s enough. I think I’ve made my point.