RHR: The Optimal Human Diet

In this episode, we discuss:

The concept of an optimal human diet, why our differences matter when it comes to diet, and what foods are better for all humans to eat (and not eat)
The evolutionary perspective on diet, including archeological and anatomical evidence for meat consumption, genetic changes suggestive of adaptation to animal foods, studies of contemporary hunter-gatherers, and the lifespan of our Paleolithic ancestors
The biochemical perspective on diet, including nutrient density, caloric density and saturated fat, bioavailability, and essential vs nonessential nutrients
What we can conclude from the biochemical perspective
Potential downsides to a long-term restrictive diet approach
Why the best approach is focusing your diet on nutrient density

Show notes:

“Priority Micronutrient Density in Foods” study by Ty Beal and Flaminia Ortenzi
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Hey, everybody, Chris Kresser here. Welcome to another episode of Revolution Health Radio. There’s so much confusion about diet out there. Eggs are bad for you. Wait, eggs are good for you! Fat is bad. Wait, fat is good and carbs are bad! Skipping breakfast causes weight gain. Wait, skipping breakfast or intermittent fasting is great for weight loss and metabolic health. It’s enough to make you crazy, right? These are just a few of the many contradictory nutrition claims that have been made in the media over the past decade, and it’s no wonder that people are confused about what to eat.

In this episode, I’m going to summarize my thoughts on what constitutes an optimal human diet, based on the most current research and also an evolutionary perspective. My hope is that this will bring some clarity to all the confusion and misunderstanding that’s out there and help you make more informed and better choices for your own dietary approach. Ready? Let’s dive in.

What Is the Optimal Human Diet?

Pretty much everyone has an opinion on the optimal human diet—from your personal trainer to your UPS driver, from your nutritionist to your doctor—and they’re all convinced they’re right. Even the “experts” disagree, and they can all point to at least some studies to support their view, which is part of what makes this so confusing for the average person who just wants to figure out how to eat to promote better health and [a] longer lifespan. On the surface, the studies that these different groups of people will point to seem credible since they’re published in peer-reviewed journals and they come out of respected institutions like [the Harvard T.H. Chan School of Public Health]. This has led to massive confusion among both the general public and health professionals. As you may know, I’ve spent the last six years training over 600 healthcare practitioners in Functional Medicine, and we’ve trained over a thousand health coaches. I can tell you firsthand that there is a ton of confusion, even among people who have a lot of training in the health field. Then, of course, there’s the proliferation of diet books, the latest popular diet fad and tons of books on that, websites, social media accounts, etc. I think this has led to a justifiable mistrust in public health recommendations and media reporting on nutrition. If somebody sees the cover of TIME magazine or Newsweek magazine, and it’s a story about how eggs are going to kill you, and then a few years later, the cover is [a story about how] eggs actually aren’t that bad, and [it] just goes back and forth over and over, that’s not a situation that engenders trust; let’s just say it that way.

Millions of dollars and decades of scientific research haven’t added clarity. If anything, they’ve further muddied the waters. Why is this? As we’ll talk about in the show, I think we’ve been asking the wrong questions, and we’re using the wrong methods. If you’re confused about what to eat and frustrated by the contradictory headlines that are constantly popping up in your news feed, you are not alone. The current state of nutritional research and how the media reports on it virtually guarantees confusion. In this podcast, my goal is to step back and look at the question of what we should eat through a variety of lenses, including ancestral health, archeology, anthropology, evolutionary biology, anatomy and physiology, and biochemistry, rather than rely exclusively on observational nutrition research, which, as I will explain, is highly problematic, and that’s saying it nicely.

With this information, my hope is that you’ll be able to make more informed choices about what you eat and what you feed your family members. So let’s start with the top-line question here. What is the optimal human diet? Well, I don’t think there is one. There’s really no way to answer that question because there’s no single optimal diet for every human. When I explain this to people, they immediately get it. It makes sense to them that we shouldn’t all [follow] the exact same diet. Yet, that’s exactly what public health recommendations and dietary guidelines assume. I would argue that this fallacy is both the greatest source of confusion and the most significant obstacle to answering our key questions about nutrition. Humans share a lot in common, but we’re also different in many ways. We have different genes, different gene expression, health status, activity levels, life circumstances, and goals.

Imagine two different people—a 55-year-old sedentary male office worker who’s 60 pounds overweight and has prediabetes and hypertension, and a 23-year-old female Olympic athlete who’s training for three or four hours a day, is in fantastic health, and is attempting to build muscle for an upcoming competition. Should they eat exactly the same diet? Of course not. It’s ridiculous to assume that would be the case. Yet, diet advice is often based on that assumption. That might be an extreme example, but it’s no less true that what works for a young, single, male CrossFit enthusiast who’s getting plenty of sleep and isn’t under a lot of stress won’t work for a mother of three who also works outside the house and is burning the candle at both ends. These differences in our genes, behavior, lifestyle, gut microbiome, etc., influence how we process macronutrients, protein, carbs, fat, micronutrients, vitamins, minerals, and trace minerals, which in turn determine our response to various foods and dietary approaches.

Let me give you a few different examples. People with lactase persistence, which is a genetic adaptation that allows them to digest lactose, [which is] the sugar in milk, into adulthood are likely to respond better to dairy products than people that don’t have this adaptation. Populations with historically high starch intake tend to produce more salivary amylase, [which] is an enzyme that helps us break down starch, than populations with historically low starch intake. We know that changes to gut microbiota can help with the assimilation of certain nutrients. An example of this is that studies of Japanese people have found that their gut bacteria produce specific enzymes that help them break down the complex polysaccharides in seaweed, which can be otherwise difficult for humans to digest. Organ meats and shellfish are extremely nutrient dense and a great choice for most people, but not for someone with hemochromatosis, which is a genetic disorder that leads to aggressive iron storage, since those foods are so rich in iron. Then [there are] large, well-controlled studies involving up to 350,000 participants that have found that, on average, higher intakes of saturated fat are not associated with higher risk of heart disease. But is that true for people with certain genes that make them hyper-absorbers of saturated fat and lead to a significant increase in [low-density lipoprotein] (LDL) particle number, which is a marker that’s associated with a greater risk of cardiovascular disease?

That’s just a partial list, but it’s enough to make the key point that there are important differences that determine what an optimal diet is for each of us. But those differences are rarely explored in nutrition studies. Most research on diet is almost exclusively focused on top-down, population level recommendations, and since a given dietary approach will yield variable results among different people, this keeps us stuck in confusion and controversy. It’s also kept us stuck in what the food philosopher Gyorgy Scrinis has called the ideology of nutritionism, which he defines as, “the reductive approach of understanding food only in terms of nutrients, food components, or biomarkers like saturated fats, calories, and glycemic index, abstracted out of the context of foods, diets, and bodily processes.” In other words, it’s a focus on quantity, not quality. This is, I think, a huge mistake that we have made in our study of nutrition over the past few decades, [in] really isolating these various food components and looking at them myopically rather than thinking about the context in which those components of food appear. Are they showing up in the context of a nutrient-dense, whole foods diet? Or are they showing up in processed and refined foods where those nutrients have been fortified or added in?

Nutrition research has essentially assumed that a carbohydrate is a carbohydrate, a fat is a fat, and a protein is a protein, no matter what type of food they come in. If one person eats 50 percent of calories from fat in the form of doughnuts, pizza, candy, and fast food, and another person eats 50 percent of calories from fat in the form of whole foods like meat, fish, avocados, nuts, and seeds, they could still be lumped together in the same ‘50 percent of calories from fat group’ in most studies. Again, when I explain this to the average person, they see how ridiculous that is, and yet that is how a lot of nutrition research is done.

There are some signs that the tide is turning. Some recent studies have much better experimental designs. But the vast majority of epidemiological studies that have served as the basis for public health recommendations and dietary guidelines are plagued by this focus on quantity over quality, or what Gyorgy Scrinis calls nutritionism.

I think we can all agree that there shouldn’t be any “one-size-fits-all” approach to diet, but that doesn’t mean that there aren’t core nutrition principles that apply to everyone. This is the flip side of that coin. For example, I think we can agree that a steady diet of doughnuts, chips, candy, soda, and other highly processed and refined foods is inherently unhealthy. And most people would agree that a diet based on whole, unprocessed foods is beneficial. It’s the middle ground where we get into trouble. Is meat good or bad? If it is bad, does that apply to all meats, or just processed meat or red meat? What about saturated fat? Should humans consume dairy products? A better question than “What is the optimal human diet?” might be “What is a natural human diet?” Or, more specifically, “What is the range of foods that human beings are biochemically, physiologically, and genetically adapted to eat?” In theory, there are two ways to answer this question. We can look at evolutionary biology, archaeology, medical anthropology, and comparative anatomy and physiology to determine what a natural human diet is. And we can look at it from a biochemical perspective—what essential and non-essential nutrients contribute to human health and where they [are] found in foods, how various functional components of food influence our body at the cellular and molecular level, and how certain compounds in foods, especially those prevalent in the modern industrialized diet, damage our health by inflammation, disruption of the gut microbiome, hormone imbalance, and other mechanisms. I’m going to spend the rest of this podcast looking through each of these lenses. Let’s start with the evolutionary perspective.

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The Evolutionary Perspective

Human beings, like all other organisms in nature, evolved in a particular environment, and that evolutionary process dictated our biology and physiology as well as our nutritional needs. Isotope analysis from archaeological studies suggests that our hominid ancestors have been eating meat for at least two and a half million years. There’s also wide agreement that, going even further back in time, our primate ancestors likely ate a diet similar to modern chimps, which we now know eat vertebrates. The fact that chimpanzees and other primates evolved complex behavior like using tools and hunting in packs indicates the importance of animal foods in their diet and ours. There’s also anatomical evidence for meat consumption. The structure and function of the digestive tract of all animals can tell us a lot about their diet, and the same is true for humans. The greatest portion, about 45 percent, of the total gut volume of our primate relatives is the large intestine, which is good for breaking down fiber, seeds, and other hard-to-digest plant foods. In humans, the greatest portion of our gut volume, about 56 percent, is the small intestine, which suggests we’re adapted to eating more bioavailable and energy-dense foods like meat and cooked starches, [which] are easier to digest.

Some advocates of plant-based diets have argued that humans are herbivores, because of our blunt nails, small mouth opening, flat incisors and molars, and relatively dull canine teeth, all of which are characteristics of herbivorous animals. But this argument ignores the fact that we evolved complex methods of procuring and processing food, from hunting, to cooking, to using sharp tools to rip and tear flesh. These methods and tools take the place of anatomical features in other animals that serve that same function. Humans have relatively large brains and small guts compared to our primate relatives. Most researchers believe that consuming meat and fish is what led to our larger brains and smaller guts compared to other primates because animal foods are more energy dense, and they’re easier to digest than plant foods. We can also look at genetic changes that are suggestive of adaptation to animal foods. Most mammals stop producing lactase, [which is] the enzyme that breaks down lactose, after they’re weaned. But in about one-third of humans worldwide, lactase production persists into adulthood. This allows those humans to obtain nutrients and calories from dairy products without becoming ill. If we were truly herbivores that aren’t supposed to eat animal foods at all, we would not have developed genetic adaptations like that.

Then we have studies of contemporary hunter–gatherers. Groups like the Maasai, Inuit, Kitavans, Tukisenta, !Kung, Aché, Tsimané and Hadza. When we look at research on those extant hunter–gatherer groups in the 20th century, without exception, they consume a combination of animal and plant foods, and they go to great lengths to obtain plant or animal foods when they’re in short supply. For example, in one analysis of field studies of almost 230 hunter–gatherer groups, researchers found that animal foods provided the dominant source of calories, 68 percent, compared to gathered plant foods, which was 32 percent. Only 14 percent of those societies got more than 50 percent of their calories from plant foods. Another report on 13 different field studies of the last remaining hunter–gatherers carried out in the early and mid-20th century found similar results. Animal food comprised 65 percent of total calories on average, compared with 35 percent from plant foods. The amount of protein, fat, and carbohydrates, the proportion of animals versus plants, and the macronutrient ratios consumed vary, but an ancestral population following a completely vegetarian or vegan diet has never been discovered.

What about the lifespan of our Paleolithic ancestors? Critics of Paleo or ancestral diets often claim that they’re irrelevant because our Paleolithic ancestors all died at a young age. In other words, “Why bother even looking at what our ancestors ate? We want to live longer lifespans than they did, so we should be updating our approach.” This is a common myth, and it’s been debunked over and over by anthropologists. While average lifespan is and was lower among hunter–gatherers than ours is today, that’s heavily skewed by high rates of infant mortality, which is mostly due to lack of emergency medical care and other factors in those populations. The anthropologists Gurven and Kaplan studied lifespan in extant hunter–gatherers and found that, if they survived childhood, their lifespans are roughly equivalent to our own in the industrialized world, 68 to 78 years. This is notable because hunter–gatherers today survive only in isolated and marginal environments like the Kalahari Desert, the Amazon rainforest, and the Arctic circle. What’s more, in many cases, hunter–gatherers reach those ages without acquiring the chronic diseases that are so common in Western countries. They’re less likely to have heart disease, diabetes, dementia and Alzheimer’s [disease], and many other debilitating chronic conditions. For example, one study of Tsimané people in Bolivia found that they have a prevalence of atherosclerosis 80 percent lower than ours in the United States, and that nine in 10 Tsimané adults aged 40 to 94 had completely clean arteries and no risk of heart disease whatsoever. The researchers also found that the average 80-year-old Tsimané male had the same vascular age as an American in his mid-50s. The idea that our hunter–gatherer ancestors were all dropping dead when they were 30 or 40 and lived with miserably poor health is just not supported by the research.

Fat is bad! Wait, fat is good! If you’re confused about the optimal human diet, you’re not alone. Tune into this week’s episode of Revolution Health Radio to find out what you should be eating to thrive. #chriskresser #diet #nutrientdensity

When you put all this evidence together from the evolutionary perspective, it suggests three themes. Number one, meat and other animal products have been part of the natural human diet for at least two and a half million years. Number two, all ancestral human populations that have been studied ate a combination of plants and animals. And number three, human beings can survive on a wide variety of foods and macronutrient ratios within the general template of plants and animals they ate.

The Biochemical Perspective

Let’s move on to the biochemical perspective. Understanding ancestral diets and the relationship to the health of hunter–gatherer populations is a good starting place, but on its own, it doesn’t prove that such diets are the best option for modern humans. To know that, we need to examine this question from a biochemical perspective, as well. We need to know what nutrients are essential to human health, where they’re found in food, and how various components of the diet and compounds in food affect our physiology, both positively and negatively. The good news is [that] there are tens of thousands of studies in this category, and collectively, they bring us to the same conclusion that we just reached when we were looking through the evolutionary lens. A whole foods diet that contains both plants and animals is the best, and, in some cases, only, way to meet our nutrient needs from food.

Let’s start with nutrient density. This is arguably the most important concept to understand when it comes to answering the question [of] what [we] should eat. The human body requires at least 40 different micronutrients for normal metabolic function, and maximizing the nutrient density of our diet should be the primary goal because deficiencies of any of these nutrients can contribute to the development of chronic disease and even shorten our lifespan. There are two types of nutrients in food: macronutrients and micronutrients. Macronutrients refer to the three food substances required in significant amounts in the human diet, namely protein, carbohydrates, and fat. Micronutrients are vitamins, minerals, and other compounds required by the body in smaller amounts for normal physiological function.

The term “nutrient density” refers to the concentration of micronutrients and amino acids, which are the building blocks of protein, in a given food. While carbohydrates and fat are important, they can be provided by the body for a limited amount of time when we can’t get enough of them through diet, except for the essential omega-6 and omega-3 fatty acids. On the other hand, micronutrients and the essential amino acids found in protein cannot be manufactured by the body, and that means they must be consumed in the diet. So, with this in mind, what are the most nutrient-dense foods? There are a lot of studies that have tried to answer this question. In one of the most comprehensive pieces of research, which I’ll call the Maillot study because that is the name of the lead author, the researchers looked at seven major food groups and 25 subgroups, characterizing the nutrient density of these foods based on the presence of 23 qualifying nutrients. They found that the most nutrient-dense foods were number one, organ meats, number two, shellfish, number three, fatty fish, then lean fish, vegetables, eggs, poultry, legumes, red meat, milk, fruits, and nuts. As you can gather, eight of the 12 most nutrient-dense categories of foods are animal foods. All types of meat and fish, vegetables, fruit, nuts, and dairy were more nutrient dense than whole grains, which received a score of only 83, relative to organ meat’s score of 754, shellfish’s score of 643, fatty fish [at] 622, and lean fish [at] 375.

Now, there are a few caveats to the Maillot analysis. Number one, it penalized foods for being high in saturated fat and calories. Number two, it did not consider bioavailability. Number three, it only considered essential nutrients. In this conventional perspective, nutrient-dense foods are defined as those that are high in nutrients but low in calories and saturated fat. But recent evidence has found that saturated fat doesn’t necessarily deserve its bad reputation and can be part of a healthy diet. Likewise, some foods that are high in calories, like red meat or full-fat dairy, are also rich in key nutrients and, again, can be beneficial when part of a whole foods diet. Had saturated fat and calories not been penalized in this Maillot study, foods like red meat, eggs, dairy products, and nuts and seeds may have appeared even higher on the list. We have a more recent study, just published in March 2022, called “Priority Micronutrient Density in Foods.” This was by Ty Beal and Flaminia Ortenzi, and it was published in the journal Frontiers in Nutrition. This was a great addition to understanding nutrient density of food because in this study, they did not penalize foods for saturated fat content. They also considered the importance of bioavailability, which I’m going to come back to shortly. And what they found was that four of the seven most nutrient-dense foods were organ meats—liver, kidney, heart, and spleen. The way they ranked foods [meant] a lower score was better in terms of nutrient density. I just want to give you an idea of how incredibly nutrient dense organ meats and shellfish and small dried fish, which were some of the other foods in the top seven, are compared to grains and even nuts and seeds and some of the foods that the conventional world tends to promote as being nutrient dense.

Liver was at the top of the list [with] a score of 11. Spleen was next at 62. Small dried fish, 65. Dark leafy green vegetables, 72. Bivalves, like mussels, were 90. Kidney was 125, and heart was 163. Then crustaceans, 193. Goat, 205. Beef, 275. Eggs, 281. So even within those animal foods, liver is several times more nutrient dense than, for example, goat, beef, or eggs. Let’s go down to vitamin A-rich fruits and vegetables, [which] was 297. Still pretty good. Then you go down to quinoa, which is a more recent addition to the diet for some people but [is] often thought of as a nutrient powerhouse, [and] that’s 789. Then we’ve got chicken [at] 1103, so definitely less nutrient dense than red meat and organ meats. You’ve got other fruits, which [was] 1147. You’ve got whole grains, which was 1768. You’ve got nuts, which were 1829, and you’ve got refined grains, which was over 4000. It says “4000 plus” because they’re so devoid of nutrients that it went off the scale. So, again, keep in mind that liver was 11, and now we’re talking about whole grains being 1768.

This is a profound difference, and this was probably the most advanced nutrient density study that’s ever been done because it considered bioavailability. That’s a crucial factor that was not considered in previous studies on nutrient density. It refers to the portion of a nutrient that’s absorbed in the digestive tract. The amount of bioavailable nutrients in food is always lower than the amount of nutrients the food contains, and I really don’t think people understand this. I think if they look at a food label and see spinach has 115 milligrams of calcium, [they think], “Awesome, I’ll just eat that spinach and I’ll be set for calcium.” But the bioavailability of calcium from spinach is only five percent. So out of that 115 milligrams of calcium that you see on paper for spinach, only six milligrams is going to be absorbed. This means [that] you’d have to consume 16 cups of spinach to get the same amount of bioavailable calcium that you would get from one glass of milk because the bioavailability of calcium in dairy is far, far higher. The bioavailability of protein is another really important thing to consider when it comes to nutrient density. Researchers now use a measure called the protein digestibility-corrected amino acid score, or PDCAAS, which combines the amino acid profile of a protein with a measure of how much of that protein is absorbed during digestion in order to assess protein bioavailability. The PDCAAS rates proteins on a scale of zero to one, with values closer to one representing more complete and better absorbed proteins than values that are closer to zero.

If you look at that scale, animal proteins have much higher scores than plant proteins. Casein, which is a protein found in dairy products, eggs, whole milk protein, whey, and chicken all have scores of one, indicating excellent amino acid profiles and high absorption, with turkey, fish, and beef close behind. Plant proteins, on the other hand, tend to have much lower scores. Legumes, on average, score around 0.7, rolled oats scored 0.57, lentils and peanuts are 0.52, tree nuts are 0.42, and whole wheat is 0.42. When you actually factor bioavailability in, as Ty Beal and Flamini Ortenzi did in their most recent study on nutrient density, we see that animal products, and particularly organ meats, small dried fish, and shellfish, dramatically outperform most plant foods with the exception of dark leafy green vegetables. This is a really big deal. It’s certainly not something that’s factored into current conventional dietary recommendations, and it’s also not something that tends to come up in the discussion of plant-based diets versus diets with animal foods. I’ve discussed this on the Joe Rogan [Experience] a few times and have done my best to get the word out, but I find that in my conversations with people of all backgrounds, whether just lay people or healthcare practitioners or even researchers, this important consideration of nutrient density and bioavailability is often not very well understood.

Another question when it comes to nutrient density is which nutrients we [should] be thinking about. All these studies on nutrient density, including the most recent Ty Beal and Flaminia Ortenzi study, tend to focus on essential nutrients. In a nutritional context, the term “essential” doesn’t just mean important; it means necessary for life. It means that we need to consume these nutrients from the diet because our bodies cannot produce them on their own and we cannot live without these nutrients, or at least we’ll experience very, very significant problems if we don’t get them. Focusing on these essential nutrients makes sense for all those reasons. But over the past few decades, many nonessential nutrients have been identified that we now know are also important to our health, even if they are not strictly necessary for us to survive. These include things like carotenoids, polyphenols, flavonoids, lignans, and fiber. Many of these nonessential nutrients are found exclusively in fruits and vegetables. Had these nutrients been included in those nutrient density studies, to be fair, fruits and vegetables would have likely scored higher than they did.

I didn’t just share all that information about the nutrient density of meat and animal foods to convince you that you should only eat meat and animal foods. I shared it because those foods are often maligned, and people often have the mistaken impression that fruits and vegetables are higher in essential nutrients than animal foods are, which is simply not correct.

Conclusions From the Biochemical Perspective

So, what can we conclude from the biochemical perspective? When we look at a natural human diet through the lens of biochemistry and physiology, we arrive at the same conclusion that we arrived at when we looked at it through the evolutionary lens. Our diet should consist of a combination of organ meat, meats, fish, shellfish, eggs, fresh vegetables and fruits, nuts, and seeds and starchy plants. But how much of the diet should come from animals and how much should come from plants? Well, as I argued earlier in the podcast, the answer to this question should vary based on individual needs. If we look at evolutionary history, we see that, on average, humans obtained about 65 percent of calories from animal foods and 35 percent of calories from plant foods, but the specific ratios varied depending on geography and several other factors. I want to be clear here—that doesn’t mean that two-thirds of what you put on your plate should be animal foods. Remember, calories are not the same as volume, i.e., what you actually put on your plate. Meat and animal products are much more calorie-dense than plant foods. For example, one cup of broccoli contains just 30 calories, compared to 338 calories for a cup of beef steak. This means that even if you’re aiming for 50 to 70 percent of calories from animal foods, plant foods would typically take up between two-thirds and three-quarters of the actual space on your plate. When we consider the importance of both essential and nonessential nutrients, it also becomes clear that both plant and animal foods play an important role because they’re rich in different types of nutrients. Dr. Sarah Ballantyne has written very eloquently about this in a series on her blog. I’m pulling some of the material from there. Plant foods tend to be rich in vitamin C, carotenoids like lycopene, beta-carotene, lutein, and zeaxanthin, diallyl sulfides from the allium class of vegetables like garlic, polyphenols, flavonoids, dithiolethiones, lignans, plant sterols and stanols, isothiocyanates and indoles, and prebiotic fibers, both soluble and insoluble.

All those nutrients, which a growing body of modern research suggests are really important for promoting optimal health and longevity in humans, tend to be found in plant foods. Then animal foods tend to be the best sources of bioavailable forms of [vitamin] B12, iron, zinc, preformed vitamin A (which is retinol), high-quality protein, creatine, taurine, carnitine, selenium, vitamin K2, vitamin D, the long chain omega-3 fats, [docosahexaenoic acid] (DHA) and [eicosapentaenoic acid] (EPA), and conjugated linoleic acid (CLA), another beneficial fat.

So, if you only eat plants, you’re going to be favoring the nutrients that are found in plant foods—those nonessential nutrients that are very beneficial but don’t play the same roles as the essential vitamins and minerals. If you only eat animal foods and don’t eat any plants, you’re going to be favoring the essential nutrients, like the vitamins and minerals and essential amino acids, but you’re going to be missing out on the fibers and plant sterols and stanols and polyphenols and flavonoids and things that tend to be much more concentrated in plant foods.

Cautionary Thoughts on Restrictive Diets

For most of us, I think a combination of plant and animal foods makes the most sense. I know a lot of you are thinking about the carnivore diet, which is one of the most recent diet fads. I think it is probably a fad; I don’t know for sure, but my guess is that in five or 10 years, we won’t be talking about the carnivore diet so much. I could be wrong. We’ll find out. But advocates of the carnivore diet say we don’t need plant foods to be healthy and even argue that plant foods are full of toxins and can be harmful. I don’t think there is research to support either of those views. As I’ve argued, [whether] you look through the evolutionary lens or the biochemical lens, you see the same results. In the case of the evolutionary lens, all human populations that we know of have eaten a combination of animal and plant foods, and through the biochemical lens, animal and plant foods are rich in different nutrients that studies have shown are beneficial to our health. The reason that a lot of people adopt a carnivore diet in the first place is because they’re dealing with some kind of chronic health condition, often a severe one like a severe autoimmune disease, and they have not been able to find relief through any conventional or even alternative types of treatments. Then they adopt a carnivore diet, and they have an almost miraculous response. I’ve seen that firsthand in patients I’ve worked with, and I’ve even recommended the carnivore diet short-term for some patients, for that reason. I don’t want to diminish the importance of a treatment, especially a natural food-based treatment like this, that can have such a profound impact on someone’s life and take them from feeling totally debilitated to actually being able to function in their day-to-day routine. That is extremely important to people on an individual level. I don’t have any judgment toward somebody who chooses to follow a carnivore diet if it has had that kind of life-saving effect.

At the same time, I think we need to be willing to explore the potential downsides, especially long-term, of an approach like that. It doesn’t follow that something that helps in the short-term is necessarily going to be safe to do in the long-term. A perfect example of this is fasting. There’s a saying that fasting is the cure for all diseases. And if you look in the scientific literature, that almost seems to be true. Fasting can have a profound impact on almost every health condition. I’ve used fasting with my patients with all kinds of conditions like autoimmune disease, Parkinsons [disease], metabolic issues, diabetes or high blood sugar, weight loss, etc. It is one of the most effective treatments of any type that I’ve ever used in my 15 years of clinical experience. Yet, I think it’s pretty obvious what will happen if you fast for an extended period of time. The longer you fast, the less beneficial it becomes. Eventually, it will become fatal if you don’t eat any food at all for a long enough period of time. So that’s a prime example of something that can be transformative and even life-saving in the short-term, but can cause significant problems over the long-term.

I would say that the carnivore diet may fall into that category, as well. In some ways, I think it acts almost like a fast because meat is digested much farther up in the digestive tract. It’s what we would call a “low -residue” diet, and it gives our colon and the lower part of our small intestine a rest. I believe that a lot of chronic diseases that plague us today are significantly driven by disrupted gut microbiome, leaky gut, and a lot of other gastrointestinal pathologies. So it makes sense to me that something that would allow us to give our gut an extended period of rest and the ability to heal and recover while also still providing us with high concentrations of bioavailable forms of essential nutrients could be very healing for a lot of people. That doesn’t necessarily mean that’s the best approach for the average person who is pursuing optimal health and longevity. I think that’s another important point about the carnivore diet, or any other special therapeutic diet—we have lots of examples of approaches that are beneficial for certain populations, but are not beneficial for other people who are not dealing with that particular health condition. For example, a low-FODMAP diet has been shown to reduce symptoms in people with [irritable bowel syndrome] (IBS). That doesn’t mean everybody should be on a low-FODMAP diet. The autoimmune protocol (AIP) has some good research behind it, which removes nuts and seeds, dairy, nightshades, grains, and legumes. But that would be an unnecessarily restrictive diet for the average person to follow, and I would never recommend that someone without an autoimmune condition, and even sometimes people with autoimmune conditions that aren’t sensitive to those foods, follow that dietary approach for a long period of time, because there’s a potential of nutrient deficiencies developing and there are lots of foods that are, for most people, perfectly healthy and beneficial that would be excluded in a dietary approach like that. I think we need to be very careful about extrapolating therapeutic diets that can benefit people in the short-term to, “Oh, this is something that everybody should be doing for the long-term.” Unfortunately, that seems to happen with approaches like a ketogenic diet or a carnivore diet.

Focus on Nutrient Density

Okay, let’s circle back. We’ve talked about how anthropology and archaeology suggest that it’s possible for humans to thrive on a variety of food combinations and macronutrient ratios within the basic template of whole, unprocessed animal and plant foods. But let me give you a few examples of just how variable these diets can be. The Tukisenta of Papua New Guinea consume almost 97 percent of calories in the form of sweet potatoes. They basically [only] eat sweet potatoes, and the few different types of calories that they get come from the insects that they might eat on the sweet potatoes. Their diet is very limited to sweet potatoes, yet they still seem to be healthy and doing pretty well. Then we [also] had traditional Okinawans, who had a very high intake of carbohydrate and a low intake of animal protein and fat, and the Okinawans are renowned for their longevity. If we [only] looked at those two cultures, we might think [that] a 100 percent plant-based diet is the way to go. On the other hand, we know about cultures like the Maasai, and the traditional Inuit, which consumed an extremely high percentage of calories from animal protein and fat, especially at certain times of year when they consumed almost no plant foods at all. They are also remarkably healthy and have longevity, notwithstanding the lack of emergency medical care and other factors that we mentioned earlier. So how much animal versus plant food you consume should really depend on your specific preferences, needs, and goals.

For most people, a middle ground seems to be what works best, sticking with the averages that have been observed in the studies of multiple hunter-gatherer cultures around the world. So, somewhere around two-thirds of calories from animal foods, and one-third of calories from plant foods. And remember, we’re talking about calories, not volume. Two-thirds of calories from animal foods and one-third of calories from plant foods would actually look like two-thirds or even three-quarters of your plate being plant foods and one-third or one-quarter of your plate being animal foods.

I hope this has been helpful in bringing more clarity and understanding to what foods might comprise an optimal diet for most of us. The takeaway here is that, yes, there are some general principles that I think we can apply to human beings, like the ideal combination [for most people] seems to be [both] plant and animal foods, rather than exclusively plant foods and/or exclusively animal foods. And also that there’s tremendous room for variation within that basic template of a combination of animal and plant foods. There really is no “one-size-fits-all” approach. Everything from our genes, to our health status, to how much we’re exercising and what our goals are will influence what the specific optimal approach is for you or me.

All right, that’s it for today. Please keep sending your questions in to ChrisKresser.com/podcastquestion, and I’ll see you next time.

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