by Rob Palmer

Greetings, dedicated readers of the IHP blog (and anyone else who finds themselves here, intentionally or not)! I’m endeavoring to write a new type of blog post, one which may become a theme on the blog: a good enough (yet still likely woefully incomplete) fact-check of health-related books. The goal is to give myself and readers a better sense of how much to trust the claims within a given book. The approach is simple: I will take a sample of important or random referenced claims made within the book, then read the referenced source in order to determine if the source supports the claim.

Why is this approach helpful? Because many times authors cite sources to support claims that the sources actually don’t support, or at least don’t support the claims well. The net effect is a misled and misinformed readership, the consequences of which can be harmful. By assessing a sample of claims, it’s theoretically possible to get a crude sense for the veracity of the overall text. For example, if eight out of eight assessed claims are well-supported by the referenced sources, then it’s likely that the book is trustworthy. On the other hand, if only one or two claims is well-supported, then there’s good reason to regard the text with suspicion.

This approach to vetting books is, as previously stated, woefully incomplete for many reasons, two of which are 1) I won’t fact-check every claim made in the book (unless you pay me to!) and 2) I likely won’t research counterarguments and evidence that would rebut the claim in question. I’d like to emphasize the latter point, since it’s near and dear to my academic heart. Authors often cherry-pick information that supports the argument they’re advancing. Consequently, the referenced evidence may indeed support the argument, yet the vast majority of the evidence on the topic may refute the particular claim. Having literature be peer-reviewed can remedy this issue, since subject-matter experts can use their wealth of knowledge on the subject to scrutinize claims. I’m not a subject-matter expert, however. I’m a medical student with a wee bit of free time. Consequently, I likely can’t determine when someone is cherry-picking evidence and omitting (intentionally or not) strong evidence that refutes the claim they’ve made. All that to say, take the content of these posts with a grain of salt. They’re not meant to be the definitive assessment of a given text, just a way to help me and you to gain a better (yet still imperfect!) perspective on the veracity of a text. And in case anyone’s curious, I’m pretty confident I got the idea for this approach from the book, “Algorithms to Live By,” by Brian Christian and Tom Griffiths, though I listened to the book a few years ago and have a hazy memory of the content.

The first book I’d like to explore with this method is “The Carnivore Code: Unlocking the Secrets to Optimal Health by Returning to Our Ancestral Diet,” by Dr. Paul Saladino. I read the book this spring and have followed Dr. Saladino’s work online for about a year, mostly through listening to his podcast and podcasts on which he’s a guest. I have no beef with Dr. Saladino—pun intended—and support his effort to encourage people to adopt healthier lifestyles. The carnivore diet is a popular topic in the nutrition sphere, and “The Carnivore Code” seemed to be one of the best resources to help me better understand the diet and the arguments in support of it.

To be explicit, this post is not meant to be a takedown of the book or Dr. Saladino. Indeed, as I write these words, I haven’t picked citations to assess, so I don’t know what will happen with this post. I’m interested in improving my understanding of this material, and I expect (or at least hope) I can do so in an amicable manner. Now that I’ve rambled on for several hundred words without getting to the proverbial meat and potatoes of this post—the food puns are low-hanging fruit, what can I say—I’ll start with the first referenced claim, chosen at random.

The first claim comes from a chapter that tries to debunk health concerns about eating red meat. The claim is about the healthiness of the males in the Nicoya region of Costa Rica, which is a regarded as a “blue zone” of longevity. Dr. Saladino tries to rebut the claim made by Dan Buettner that the typical diet of blue zones is a diet that is primarily plant-based (though not necessarily vegetarian or vegan). The referenced claim mentions that these men have lower cardiovascular risk factors, longer telomeres, and higher levels of male sex hormones. You can find the referenced paper here, and the claims Saladino makes are stated in the abstract of the paper. So far, so good. Saladino claims later in the paragraph that the men in this region use animal fat for cooking, eat more animal foods than does the general Costa Rican population, and are regarded for their affinity for eating meat. The abstract of the paper notes that the diet of the Nicoyans is rich in rice, beans, and animal proteins and has a high fiber content—not a definitive statement for or against either Dr. Saladino or Buettner.

Reading more of the paper, I learn that yes, the researchers found that elderly men in Nicoya live longer than elderly men in the general Costa Rican population and have extraordinary longevity. The women don’t, however, and it’s not yet clear why there’s a sex difference. Of note, the researchers found that Nicoyans who migrated from the region or were born outside the region don’t have exceptional longevity, which would seem to argue that genetics aren’t a major factor. The authors note, however, that they don’t have enough information to make claims about this point (e.g., age of migration, health conditions that might have prompted migration, etc.), so the issue remains unresolved.

The authors also found that Nicoya men had lower levels of triglycerides, fasting glucose, and HbA1c than did men in the general Costa Rican population, and that both Nicoya men and women had lower total cholesterol, waist circumference, BMI, and diastolic blood pressure. In addition, as previously mentioned, they had longer telomeres and higher DHEA-S levels. The authors also note that the elder Nicoyans are taller than other Costa Ricans, which they speculate may be due to better diet and fewer infections during childhood. (The authors also note there could be a more severe survival selection for taller Nicoyans—another unsolved mystery.) There were no differences in CRP despite better cardiovascular health, which the authors speculate could be due to a greater infectious disease burden.

Interestingly enough, elderly Nicoyans were more likely to be vaccinated than other Costa Ricans, yet were much less likely to take commonly prescribed medications (e.g., lipid-lowering medications) even when medication would likely have been considered appropriate. It seems that elderly Nicoyans are well-served by the primary care system, except when they aren’t. Go figure.

Now to the juiciest part of the paper: the dietary analysis, which used the oft-criticized food frequency questionnaire. To summarize the results, the Nicoyan diet was less refined and processed and included more “quotidian” foods (e.g., rice, beans, beef, fish, chicken, light cheese, and sodas). How big were the differences? They ate three grams more of protein per day than the average 70 grams per day consumed by Costa Ricans. They also consumed one more gram of fiber per day than the national average of 23 grams per day. The glycemic index of their diet is also one point lower than the 76-point national average. The authors rightfully note that these differences are small. The Nicoya were also found to consume more saturated and trans-saturated fats, which the authors attribute to an increased use of “cheaper brands of oils,” not the use of animal fats or increased consumption of animal foods. They also drank one-half a glass of milk per day, as opposed to the seven-tenths of a cup consumed by the general Costa Rican population. Is half a glass of milk the secret to longevity? I have my doubts.

So what do I make of the claims made in “The Carnivore Code” having read the cited paper? Some of the claims seem supported, and some don’t. Yes, the Nicoya men seem to have exceptional longevity. And yes, the Nicoyans seem to eat more meat than do average Costa Ricans, which seems to support the rebuttal of Buettner’s claims about the diets of blue zones being plant-based. I’m still unsure about the claims Dr. Saladino made about the Nicoyans cooking with animal fat and that they’re regarded for their affinity for eating meat. I saw no information in the paper that supports either claim. Eating an extra three grams of protein per day (for a total of 73 grams) doesn’t make the Nicoyans seem like meat-fueled paragons of longevity. Likewise, the authors suggested that Nicoyans used “cheaper brand oils” for cooking. Could they be using lard or tallow? Maybe, though I don’t know and I don’t know the basis for Dr. Saladino’s claim.

Regardless, the Nicoyans seem to be an oddity given their extreme longevity while consuming a diet that differs from diets typically regarded as optimal for longevity (e.g., the Mediterranean diet, a low animal protein diet, etc.). In fact, the Nicoyan diet seems unremarkable, with differences from the typical Costa Rican diet so miniscule to seem largely inconsequential. That said, the quality of this evidence isn’t top-notch, so it seems appropriate to maintain a high degree of humility when considering this issue. Indeed, to quote the authors of the paper, “An important cautionary note is about over-interpreting the peculiarities of Nicoya residents in diet, biomarkers or other characteristics as proof of their causal role in explaining the Nicoya survival advantage. Much more research is needed to establish such causal links.” In other words, the authors don’t know why the Nicoyan men live so long—and seemingly neither does Dan Buettner, at least when it comes to their diet.

As mentioned at the beginning of this oh-so long post, I haven’t analyzed other research on this topic, so I don’t know what other relevant research exists. That said, I briefly skimmed a 2017 paper investigating the potential role of genetics on the longevity of the Nicoyans. The paper doesn’t comprehensively answer the question of what factors contribute to Nicoyans’ longevity, though it provides evidence that suggests genetics may play a role. As per usual, the authors recommend conducting more research on the subject, since so little is understood about the subject. All that to say, neither of these papers provide strongly compelling explanations for the Nicoyans’ longevity. Consequently, anyone claiming to know why Nicoyans live so long (e.g., Dan Buettner) has some explaining to do.

Congratulation to you, dear reader, if you’ve made it all the way through this post. Stay tuned for part two of this series, in which I plan to take another deep dive into another claim made in “The Carnivore Code.”


Azofeifa, J., Ruiz-Narváez, E. A., Leal, A., Gerlovin, H., & Rosero-Bixby, L. (2018). Amerindian ancestry and extended longevity in Nicoya, Costa Rica. American Journal of Human Biology: The Official Journal of the Human Biology Council30(1).

Rosero-Bixby, L., Dow, W. H., & Rehkopf, D. H. (2013). The Nicoya region of Costa Rica: A high longevity island for elderly males. Vienna Yearbook of Population Research11, 109–136.

Resources mentioned:

“The Carnivore Code: Unlocking the Secrets to Optimal Health by Returning to Our Ancestral Diet,” by Dr. Paul Saladino (link)

Fundamental Health Podcast, the podcast of Dr. Paul Saladino (link)

Original article can be found here.

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