Saturday, November 29, 2014

The paleolithic diet and the very provable links to our past

As the evidence in support of the Paleolithic diet continues to pile up, it's becoming more and more difficult for popular health writers and government public health agencies to ignore it. Some have gracefully conceded that they may have been wrong, while others are stubbornly doubling down on their criticisms of the diet.

Writing at The Conversation, evolutionary biologist Darren Curnoe typifies the second approach. He argues that the Paleo diet is a " largely impossible dream based on a set of fallacies about our ancestors," even positing that the diet could be harmful. His arguments are similar to Marlene Zuk's criticisms of the Paleo diet, and consequently Curnoe is wrong for the same reasons she is: he ignores evidence that doesn't fit his argument and misstates what proponents of the diet actually recommend.

The first key point to make is that the Paleo diet works. Regardless of the more abstract issues in play, like whether or not human evolution has stopped, the fact remains that people who go on some variant of the Paleo diet lose weight and improve their health, often dramatically.

Several studies back up this conclusion, all curiously absent from The Conversation piece. One 2007 study compared the Paleo diet to the Mediterranean diet and found that the former better enabled men with heart disease and type 2 diabetes to control their blood sugar. Both groups lost weight, but the Paleo group in the study naturally ate fewer calories and saw greater reductions in waist circumference. Every patient in the Paleo group was also able to bring his blood sugar down to normal levels.

Another study from 2009 similarly found that "a Paleolithic diet improved glycemic control and several cardiovascular risk factors compared to a Diabetes diet in patients with type 2 diabetes." A study of healthy but obese women found comparable results as well: the patients lost weight, reduced their liver fat; lowered their blood pressure, cholesterol and fasting blood sugar.

There are other studies that could be discussed, but you get the point. Compared to the diets deemed acceptable by the medical establishment, the Paleo diet does a better job of improving every marker for metabolic health we currently measure. Moreover, it's helping people who are most at risk for harm-- fat people, diabetics and heart disease patients.

The foundation of Curnoe's argument is that the link between a healthy diet and our Paleolithic ancestors is dubious. He cites an International Journal of Obesity article in support of this point, which argued that scientists have a difficult time determining how our biology influences our propensity to gain weight, though they know it exerts some influence. From this information, Curnoe says that the Paleo diet is based on "assumptions [that] are difficult to test or even outright wrong." But given this admitted ignorance of how evolution influences obesity, I'm curious how Curnoe or any other critic can so confidently attack the Paleo diet. If the evidence is too limited to draw a conclusion, why is Curnoe drawing a conclusion?

But there is quite a bit of evidence to draw from, and none of it offers Curnoe much help. Though human evolution hasn't stopped, research indicates that most of the human genome is composed of genes selected during the Paleolithic Era. In fact, "Many scientists ... expected that surveys of our genomes would reveal considerable evidence of novel genetic mutations that have recently spread quickly throughout different populations by natural selection... [but] most of the detectable natural selection appears to have occurred at a far slower pace than researchers had envisioned," according to this 2010 piece in Scientific American.

Such a slow pace of natural selection would explain the conclusion of this 2011 paper "that modern Homo sapiens are still adapted to an ancestral environment ... hunter–gatherers ... exhibit superior health markers, body composition, and physical fitness compared with industrialized populations." If you doubt the diseases of civilization hypothesis, follow the link and checkout the copious footnotes listed in support of the argument. Far from dubious, the link between a healthy diet and our evolutionary history has been well established.

Parenthetically, I wonder if Curnoe ever stopped and thought about the modern examples of people successfully following the Paleo diet. These individuals are living by advice he says is unsubstantiated and dangerous, yet they're getting slimmer and healthier. Such outcomes would seem to lend support to the idea that humans are indeed mismatched with their modern environment.

Curnoe also argues that it's a misnomer to describe diet and exercise habits from the Paleolithic as a single lifestyle because studies have found "a great deal of variation in the diet and behaviour" from this period. That's true to an extent, but Curnoe's statement overlooks the similarities running through the diets of all these different Paleolithic populations, particularly foods that would not have been in any of their diets. Table 4 from the 2011 paper in Research Reports in Clinical Cardiology lists items like isolated sugar and oils, cereal grains, alcohol and dairy. The modern western diet contains all of these foods in excess. Combined with too little sun exposure, lack of sleep and limited physical activity, this is a recipe for a very unhealthy population.

 I want to reiterate that a healthier society is what we're after. The questions posed by anthropologists and evolutionary biologists are secondary to this goal, and we've found a diet that helps us reach it. So in summary, I'll say the same thing to Curnoe that I said in response to Zuk's book last year: "We have evidence from thousands of people who have documented their experiences on a Paleo diet, and the results are remarkable. People from all walks of life have lost weight, beaten eating disorders, reversed diabetes and heart disease — and all by living a lifestyle that Zuk says is 'misguided nostalgia.'" Why anyone would attempt to obscure or ignore this fact is beyond me.

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