Interview with Chris Kresser, About His Excellent New Book “Your Personal Paleo Code”

Your Personal Paleo Code:
The 3-Step Plan to Lose Weight, Reverse Disease, and Stay Fit and Healthy for Life

Dr L: What is the Paleo diet?

Chris: The Paleo diet emphasizes foods humans are biologically adapted to eat—such as meat, fish, vegetables, fruits, nuts, and seeds—and excludes foods that have only recently (on the evolutionary timescale) become available, such as grains, legumes, industrial seed oils, and refined sugar.

Dr L: How is your book different from other Paleo books?

Chris: While most Paleo books exclude all foods that weren’t consumed during the Paleolithic era, I argue that some agricultural foods—such as dairy products, potatoes and other nightshade plants, and even certain grains—are healthy when well-tolerated by the individual. I also stress that there’s no “one-size-fits-all” approach when it comes to nutrition, and that the key to succeeding with any dietary approach (including Paleo) is personalizing it to meet your unique needs.

Dr L: What’s your personal story? What led you to the Paleo movement?

Chris: I became ill while traveling in Asia in my early twenties and struggled for more than a decade to recover my health. Along the way I discovered Paleo and it was the turning point in my recovery.

Dr L: What can we learn from our ancestors and people who still follow a traditional diet and lifestyle?

Chris: Studies of contemporary hunter-gatherers suggest they are largely free of the chronic inflammatory diseases that have become epidemic in the industrialized world. They have far fewer modern illnesses—like metabolic syndrome, cardiovascular disease, obesity, some cancers, and autoimmune disease—and they are superior in every measure of health and fitness, including blood pressure, insulin sensitivity, body mass index, waist-to height ratio, oxygen consumption, vision, and bone density. Comparative studies have shown that these remarkably healthy traditional cultures have certain dietary and lifestyle principles in common. By emulating these principles, we can regain our health.

Dr L: But didn’t cavemen die young? Why should we emulate their ways?

Chris: It’s true that our Paleo ancestors had average life spans shorter than ours today. However, these averages don’t factor in challenges largely absent from modern American lives: high infant mortality, violence and accidents, infectious diseases, and lack of medical care. Studies suggest that when these factors are considered, our ancestors had life spans roughly equivalent to our own. Even more important, they reached these ages without any signs of the chronic inflammatory and degenerative diseases that we consider to be normal in developed countries, including obesity, type 2 diabetes, gout, hypertension, cardiovascular disease, and some cancers.

Dr L: Why was agriculture “the worst mistake in human history”?

Chris: Hunter-gatherers practiced “the most successful and longest-lasting lifestyle in human history,” according to scientist and author Jared Diamond, and were all but guaranteed a healthy diet because of the diversity and nutrient density of the foods they consumed. Once humans switched to agriculture and became more sedentary, our species’ naturally robust health declined. For example, in places where agriculture was adopted, tooth decay and anemia due to iron deficiency became widespread, average bone density and height decreased, and infant mortality increased.

Dr L: What does it mean that people are “mismatched” to our current environment?

Chris: Like it or not, we humans are animals. And like all animals, we have a species-appropriate diet and way of life. When animals eat and live in accordance with the environment to which they’ve adapted, they thrive. Cats, with their sharp teeth and short intestinal tracts, evolved to be carnivores, so when we feed them grain-rich kibble, they develop kidney trouble and other woes. Humans lived exclusively as hunter-gatherers until very recently, eating the meat they hunted, the fish they caught, and the vegetables, fruits, and tubers they picked while on the move. The agricultural and industrial revolutions profoundly altered humans’ food supply and way of life, and these changes have led to a precipitous decline in our health.

Dr L: Why aren’t whole grains the nutritional powerhouses they’re made out to be?

Chris: Grains are one of the least nutrient-dense foods available, especially when they’re highly refined (i.e., flour).This is notable because 85 percent of grain consumed in the U.S. is consumed in refined form. But whole grains aren’t that much better, in part because they contain anti-nutrients called phytates which bind to minerals like calcium, iron, zinc, and manganese, making them more difficult to absorb. Phytates also interfere with protein absorption. If a food contains nutrients that you can’t absorb, you’re not going to reap their benefits. In addition to their generally low nutrient density and potential toxicity, many grains contain proteins (e.g., gluten) capable of provoking an immune response or adverse reaction in as many as one in ten people.

Dr L: Aren’t vegetarian and vegan diets healthier than omnivorous diets?

Chris: Early studies did suggest that vegetarians have lower rates of heart disease and longer life spans than omnivores. The early studies were poorly designed and subject to confounding factors (e.g., vegetarians tend to be more health conscious on average than the general population, so there could be other factors explaining their longevity, such as more exercise, less smoking, etc.). Newer, higher-quality studies that have attempted to control for these confounding factors haven’t found any survival advantage in vegetarians. For example, one study compared the mortality of people who shopped in health food stores (both vegetarians and omnivores) to people in the general population. They found that both vegetarians and omnivores in the health food store group lived longer than people in the general population. This suggests, of course, that eating meat in the context of a healthy diet does not have the same effect as eating meat in the context of an unhealthy diet. A very large study performed in the U.K. in 2003 including over 65,000 subjects corroborated these results: no difference in mortality was observed between vegetarians and omnivores.

Dr L: Doesn’t red meat cause heart disease and cancer?

Chris: It’s true that some studies have shown an association between red meat and both heart disease and colon cancer over the years, but those studies often suffer from the same “healthy user bias” that I described above (i.e., because red meat has been perceived as “unhealthy,” people that eat it are more likely to engage in other behaviors that really are unhealthy, such as smoking). Some recent, very large studies (with more than a million participants) have found no association between heart disease and red meat consumption. In addition, if red meat caused heart disease, we’d expect to see higher rates of heart disease in omnivores than in vegetarians. This is not the case (when the “healthy user bias” is controlled for). The story is much the same with red meat and cancer. When confounding factors are eliminated, the association between red meat and cancer disappears. In fact, a large review published in the prestigious journal Obesity Reviews in 2011 found that current evidence does not support an association between red meat consumption and colon cancer.

Dr L: Does eating cholesterol and saturated fat really cause heart disease?

Chris: For decades we’ve been told that eating saturated fat increases cholesterol levels in the blood and that high cholesterol levels clog arteries and cause heart disease. But does the research actually support that theory? It’s true that some studies show that increased saturated-fat intake raises blood-cholesterol levels. But these studies are almost all short-term, lasting only a few weeks. Longer-term studies have not shown an association between saturated-fat intake and blood cholesterol levels. In fact, of all of the long-term studies examining this issue, only one of them showed a clear association between saturated-fat intake and cholesterol levels, and even that association was weak. Perhaps saturated fat contributes to heart disease by some mechanism other than raising cholesterol? Not according to the research. A large review of twenty-one studies covering almost 350,000 participants found no association between saturated-fat intake and cardiovascular disease. Moreover, studies on low-carbohydrate diets (which tend to be high in saturated fat) suggest that they not only don’t raise blood cholesterol but have several beneficial effects on cardiovascular-disease risk markers. 

Dr L: Why is celiac disease just the tip of the iceberg when it comes to gluten intolerance?

Chris: Until recently, the mainstream view of gluten intolerance has been relatively black-and-white: either you have celiac disease (CD), in which case you’re intolerant to gluten, or you don’t, in which case you can eat it without fear. This all-or-nothing view has led physicians to tell patients who suspect they’re sensitive to gluten but who test negative for CD that they’re simply imagining the affliction. But recent research has made it clear that it’s possible to have gluten intolerance without having celiac disease—a condition known as “non-celiac gluten sensitivity” (NCGS)—and that gluten intolerance is more a spectrum of conditions than a single condition, with full-blown CD on one end, complete tolerance to gluten on the other, and NCGS in the middle. While research on the incidence of NCGS is ongoing, some recent studies suggest that it may affect as many as one in ten people, or approximately 30 million Americans. 

Dr L: Why is the concern about mercury in fish overblown?

Chris: The reason mercury is potentially harmful is that it binds to selenium-dependent enzymes (aka “selenoenzymes”) and inactivates them. Selenoenzymes are crucial to protecting the body from oxidative damage. If you get exposed to too much mercury, it will bind to selenium and deplete your selenoenzymes. However, if you’re consuming more selenium than you are mercury, the depleted selenoenzymes will be restored faster than they are inactivated by mercury. In this case you would not experience toxic effects from eating food that has some mercury in it. What this means in the context of fish consumption is that if a fish has more selenium than mercury, it’s safe to eat. Fortunately the vast majority of commonly eaten ocean fish fit this description, with the exception of swordfish.

Dr L: Dairy products: healthy or unhealthy?

Chris: Dairy often gets a bad rap in the health and nutrition world. It’s been maligned by some for its high saturated fat content and condemned by others as unfit for human consumption. However, you might be surprised to learn that the evidence doesn’t support this stance. A 2012 paper published in the European Journal of Clinical Nutrition reviewed sixteen studies examining the relationship between high-fat dairy intake, obesity, and cardiovascular and metabolic disease. In the majority of studies reviewed, high-fat dairy intake was either inversely associated with obesity and metabolic disease (meaning that those who ate the most high-fat dairy foods had the lowest risk for these conditions) or not associated with them at all. In addition, some compounds in high-fat dairy products—such as butyrate, phytanic acid, trans palmitoleic acid, and conjugated linoleic acid—have been shown to have beneficial effects. Dairy is also a good source of fat-soluble vitamins like retinol (active vitamin A) and vitamin K2, which are difficult to obtain elsewhere in the diet. All of this said, whether dairy is a beneficial addition to the diet depends on individual tolerance: some people are sensitive to the proteins and sugar in dairy and will therefore need to avoid it completely or only consume dairy foods that are low in lactose (such as fermented dairy, ghee, and butter).

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