Table of Contents
- Background and Introductions
- There Are Serious Problems with Epidemiological Research
- No, Vegetarians and Vegans Don’t Live Longer
- Is There a Connection between Red Meat and Cancer?
- Does Saturated Fat Increase Your Blood Cholesterol?
- Where (and When) Conventional Ideas about Saturated Fat Come From
- Will Eating Animal Protein Shorten Your Lifespan?
- Did the Sugar Industry Influence How We Think about Saturated Fat?
- Red Meat and TMAO: Red Herring or Meaningful Association?
- Does Fish Increase Your Risk of Diabetes?
- Correlation Is Not Causation
- Here, We Agree: There Should Be Lots of Plants on Your Plate
- What Happens When You Give Up Nutrient-Dense Animal Protein
- Is the Carnivore Diet Healthy? Here Are My Theories
On Sept. 27, my debate with Dr. Joel Kahn on the Joe Rogan Experience on the merit of including meat in a healthy diet lasted almost four hours. There are very few well-structured debates on this topic, and Joe did a great job of facilitating a lengthy discussion on such a controversial topic.
I’d certainly encourage all of you to watch or listen to the recording, but if you don’t have a chance to listen to it all, I’ll provide a summary of the highlights in this article.
You can also check out “Why Eating Meat Is Good for You,” the cornerstone page that we put together in preparation for the debate. It outlines my key arguments and contains links to relevant blog articles and studies categorized by topic.
For those who don’t know him, Dr. Kahn is a 42-year vegan who attended the University of Michigan medical school. He also did training in internal medicine and cardiology before opening a preventive, plant-based cardiology practice in Michigan.
Did you miss the debate on the health impacts of a vegan vs. an omnivorous diet? Not to worry! Check out this recap and find out why you should eat meat.
Of course, as many of you know, I was a macrobiotic vegan myself for many years, and a vegetarian for quite some time as well. When I was traveling around the world and became sick, it led me to question many of my earlier beliefs about vegetarianism and veganism and ultimately led me to reincorporate meat in my diet.
To kick things off, we jumped right into the problems with nutritional epidemiology. Randomized clinical trials are incredibly expensive and, in many cases, impractical, so we’re left with observational studies that look at a certain group of people and try to draw inferences from their behavior about associations with disease.
I laid out the three biggest problems with nutritional epidemiology research.
Most observational studies employ “memory-based assessments” (i.e., questionnaires), which rely solely on a person’s recollection of what they ate.
The Healthy-User Bias
When someone engages in a behavior that’s perceived as unhealthy, they are more likely to engage in other behaviors that are perceived as unhealthy and vice versa.
Low Relative Risks
In nutrition, relative risks are often so low that they are indistinguishable from chance:
In fields outside of nutrition, nobody would consider an increase in risk less than 100 percent (a doubling) to be anything worth paying attention to.
Dr. Kahn contended that if we throw epidemiology away, we throw away about 80 percent of nutrition research. Since we can’t do the randomized controlled trials, we’re really left with basic science and studies of centenarians in blue zones like Loma Linda, California.
I certainly don’t think we should throw out epidemiological research, but we should understand the limitations and look at the findings with a critical eye.
This led to a discussion of lifespan among those following different diets. I pointed out that there are eight major studies to date that have compared lifespan in vegetarians and vegans and omnivores, only five of which did a good job controlling for the healthy-user bias. Four studies sought to compare vegans and vegetarians against health-conscious omnivores, as opposed to the general population. The fifth study found did not select health-conscious omnivores as a comparison group, but it did a much better job controlling for potential confounding factors than most observational studies do.
They found that both groups had a longer lifespan than the general population, but there was no difference in lifespan between the groups. Several meta-analyses that consider all of the available studies have confirmed this finding. (1) For more information, see my article “Do Vegetarians and Vegans Live Longer than Meat Eaters?”
Dr. Kahn immediately turned to the 2015 World Health Organization (WHO) report that found an association between red meat and cancer. He argued that even though the differences are small, 50,000 people could potentially avoid colorectal cancer by avoiding red meat. Furthermore, with newer statistical methods, we can better isolate the effects of animal protein in observational studies.
I pointed out that the WHO report found only an 18 percent increased risk of cancer from eating processed meat, and a two percent increased risk from eating unprocessed red meat. This means that 5.3 people of 100 eating more processed meat would develop cancer, vs. 4.5 people of 100 eating less processed meat. As many epidemiologists have suggested, these tiny differences are difficult to distinguish from chance in observational studies.
What’s more, there are several other studies that have shown no relationship between unprocessed red meat consumption and cancer. For an excellent review of the role of meat in a healthy diet, I suggest this article by David Klurfeld, the National Program Leader for Human Nutrition in the Agricultural Research Service of the U.S. Department of Agriculture and an associate editor at the American Journal for Clinical Nutrition.
We next discussed several mechanisms for how processed meat might contribute to cancer risk, with N-nitroso compounds, heterocyclic amines, heme iron, Neu5Gc, and TMAO being the most highly cited. However, these often don’t consider the context of the meat consumption. For instance, chlorophyll-rich green vegetables prevent myoglobin form being turned into nitro compounds. Similarly, certain spices and marinades have been shown to reduce the formation of heterocyclic amines.
Given this, not surprising that in all the studies of the relationship between red meat and cancer that controlled for vegetables, a greater increase was seen in people not consuming vegetables. (2) Vegetable consumption seems to confer a protective effect against any potential harm that may come from eating meat. (3)
Dr. Kahn agreed with this and encouraged listeners to at the very least eat vegetables with their meat.
We next moved to saturated fat. Dr. Kahn claimed that basic science has shown that when you eat foods rich in saturated fat, you reduce the receptors on the liver that take cholesterol out of the blood. Cholesterol stays in the blood and eventually leads to atherosclerosis. He cited a 1997 paper that analyzed the results of 395 metabolic studies where they changed the diet and measured the response to cholesterol: (4)
You add saturated fat, cholesterol skyrockets.
I took a brief look at this paper after the debate, and they did find an increase in blood cholesterol when saturated fat was replaced with complex carbohydrates, but the difference was only 9.4 mg/dL reduction in LDL. It also resulted in a reduction of HDL of 1.8 mg/dL. Many of these metabolic ward studies were also short-term feedings studies that lasted less than a month, and did not measure clinical outcomes. (5)
Dr. Kahn further argued that every major health agency in the world recommends limiting saturated fat intake. I reminded him that these agencies are often behind the times, and:
… the history of science is really the history of most scientists being wrong about most things most of the time.
In the last two revisions of the USDA dietary guidelines, they removed restrictions on total fat and cholesterol—and I wouldn’t be surprised if saturated fat is next.
The most important question, however, is not whether eating saturated fat increases blood cholesterol levels. It’s whether eating saturated fat increases the risk of heart disease. After all, if saturated fat increases blood cholesterol but doesn’t increase the risk of heart disease, why should we care about cholesterol going up?
Turns out this is exactly what studies suggest. Large reviews including hundreds of thousands of subjects have shown that there is no relationship between saturated fat or cholesterol intake and heart disease.
What Low-Carb Diets Reveal about Saturated Fat
To stress the saturated fat point further, I mentioned that several meta-analyses of randomized controlled trials have found that low-carb diets (which also tend to be high in saturated fats) have no effect on LDL cholesterol.
Moreover, low-carb diets are associated with a reduction in cardiovascular risk factors like: (6)
- Body weight
- Fasting blood glucose
- Blood pressure
- Abdominal circumference
- Plasma insulin
- C-reactive protein
Unfortunately, we seemed to get bogged down in the saturated fat issue for quite a while. Dr. Kahn consistently wanted to rely on studies from the 1950s, 60s, and 70s, which he believes are still useful if “it’s in retrospect, valid.”
I continually stressed that observational research is only useful for generating hypotheses, not coming to firm conclusions, and that:
… we can’t throw out really the highest standard of evidence, which is a meta-analysis of randomized controlled trials.
We briefly touched on animal protein and longevity. Dr. Kahn argued that the amino acids found in red meat, combined with their saturated fat content, trigger biochemical pathways at the cellular level that accelerate aging:
The amino acid mix found in animal protein is different from the amino acid mix found in vegetable protein, which is why […] plant protein beats the crap out of animal protein. This is high-level cell metabolism.
While it may be true that animal protein is associated with cancer in basic science experiments, I argued that there are:
… no studies that show that eating meat in the context of a healthy diet shortens your lifespan […] We can’t just focus on mechanistic studies. We have to look at actual endpoints that matter to people.
When you look at real endpoints, it’s clear that there is no effect on overall lifespan.
Somehow, we got dragged back to the saturated fat and blood cholesterol issue. This time, Dr. Kahn referenced the Hegsted equation, which was published in 1965 by David Mark Hegsted and described the relationship between changes in saturated fat intake and serum cholesterol. This, in combination with research performed by Ancel Keys, ultimately led to the original recommendations to reduce dietary saturated fat intake.
However, Hegsted, recently found to have been in the pocket of the sugar industry, was largely responsible for downplaying the connections between sugar consumption and heart disease, instead focusing on saturated fats as the primary culprit. (7)
What’s more, recent studies have shown that the Hegsted equation isn’t relevant in the context of low-carb diets. (8)
Dr. Kahn did not adequately address the evidence I repeatedly presented in regard to recent meta-analyses of randomized controlled trials, ultimately saying:
I stand by the fact human physiology will not change.
Dr. Kahn mentioned several studies that showed a causal relationship between increased consumption of carnitine and choline and TMAO. However, certain species of fish increase serum TMAO orders of magnitude more than meat or eggs, yet fish are associated with reduced cardiovascular risk. (9)
Moreover, only certain types of gut bacteria metabolize choline and carnitine to TMA, which is then converted in the liver to TMAO, so:
… scientists have speculated that high TMAO levels are essentially a result of a disrupted gut microbiome.
Dr. Kahn consistently relied on single studies to support his claims:
The assumption is that fish is a superfood. […] Fish intake is associated with increased risk of diabetes, I’m sorry, that’s epidemiology.
While the single study he referenced did find a slight increase in relative risk in the group consuming the most fish, I preferred to rely on the weight of evidence: (10)
Of course we can go and find one study here, one study there, that has a different result, but that’s not the scientific method. The scientific method is to look at the weight of the evidence and to continue to evaluate that over time as the evidence changes.
In this case, a 2012 meta-analysis found no association between fish intake and diabetes risk, and many studies suggest that seafood consumption is associated with a reduced risk of cardiovascular disease. (11)
One of the running themes throughout the debate was the need to realize that correlation is not causation. This is clearly illustrated by a study I mentioned in a population of hospitalized patients that found “24 diagnoses were significantly associated with the participants’ astrological signs.” (12)
The relative risks were 15 percent and 38 percent, which is on par with the 18 percent increased relative risk that was used in the 2015 WHO report that linked processed meat to cancer.
To further this point, I offered a quote from John Ioannidis:
Given the complicated associations of eating behaviors and patterns with many time varying social and behavioral factors that also affect health, no currently available cohort includes sufficient information to address confounding in nutritional association. (13)
In other words, there are so many factors that influence our health that it’s virtually impossible to parse these out in observational studies.
Vegetarians and vegans don’t necessarily live longer than omnivores. The supposed link between saturated fat and heart disease seems largely misguided. And red meat is not bad for your health.
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Dr. Kahn stressed that he believes we have more than enough data to advise the public and echoed Michael Pollan’s “Eat food, not too much, mostly plants,” noting “that is a synthesis of 50 years in nutritional research.”
This was certainly one of the few points where we could agree. As many of you readers know, my recommendation is, and always has been, that your plate should consist of two-thirds or three-quarters plant foods and the remainder animal foods.
Moreover, anyone who is making an effort to be conscious about their diet, whether vegan or omnivore, is going to be much better off than someone consuming a Standard American Diet full of processed foods.
This segued into a discussion of the benefit of keeping that one-quarter of your plate as nutrient-dense animal protein. I contended that vegetarians and vegans are often deficient in many nutrients, with vitamin B12 representing the biggest issue:
Some of the effects of B12 deficiency are irreversible. It’s a pretty serious thing.
Moreover, many vegans and vegetarians are only measuring serum B12, which will only be affected in late-stage B12 deficiency, and even those who are supplementing may not be getting enough.
Dr. Kahn agreed that it was something to keep an eye out for:
It’s responsible for a healthcare practitioner to advise somebody eating plant-based to take vitamin B12. […] I don’t advise my patients to rely on food because there’s neurologic and hematologic potential for trouble.
He demonstrated how easy it was to take the supplements necessary to prevent B12 and other deficiencies, saying:
My patients are totally complete. The industry has provided solutions to a relatively simple problem.
However, I maintained that this “does beg the question of whether we should be following a diet that can’t meet our essential nutrient needs.” My position has always been that we should be getting as much of our nutrients from food as possible.
Just some of the other nutrients that are an issue with vegetarian and vegan diets include bioavailable zinc, calcium, taurine, creatine, vitamin A, EPA, and DHA. For those vegans and vegetarians who are not ideologically opposed to eating small amounts of animal foods, even just one clam oyster and four grams of liver per day would completely meet your needs for vitamin B12, zinc, copper, and choline.
Finally, Joe asked about the carnivore diet, and how so many people could be experiencing benefits from eating meat alone. I offered my theory that the carnivore diet mimics some of the benefits of fasting but allows people to persist for longer since it’s providing some nutrition.
The carnivore diet is essentially like a gut rest or a fast.
Of course, this is all speculation:
We don’t yet have any evidence, but meat is absorbed very high up in the digestive tract, and so when you only eat meat, it’s a low residue diet. There’s nothing leftover to irritate or inflame the gut.
I’m certainly empathetic to those who find that the carnivore diet works for them, but it does not mean that there aren’t potential consequences to the diet in the long-term.
Dr. Kahn pointed out that since these people aren’t consuming sugar or fibrous vegetables, they may be hyper-efficient at absorbing nutrients like vitamin C. While there are anecdotal reports of individuals who have tracked their nutrient status, I think we don’t yet have the evidence say that this does not result in nutrient deficiencies.
From an evolutionary perspective, every culture we know of that has been studied ate some combination of animal and plant foods, even though the ratio varied from place to place.
Join the Debate! Do You Eat Meat?
And there you have it, almost four hours boiled down into the key highlights and takeaways! I’d love to hear what you thought about the debate in the comments below. Be sure to also check out the cornerstone page and share it with your friends and family. If you’re interested in delving into the research behind this topic, take a look at the bibliography page.
I hope this debate and these resources serve as a big step towards clearing up the confusion and misunderstanding about this topic.