Why are legumes banned by the Paleo Diet?

Hey Folks! You would think that I’m finished critiquing the Paleo diet after the last post, but I want to focus on one major issue in this post: why are legumes banned by the Paleo Diet? Legumes (peas, beans, lentils, chickpeas, peanuts, etc.) are widely considered to be sustainable and healthy sources of protein, fiber, minerals, B-vitamins, folic acid, and other nutrients. They are unique in the plant kingdom in that they produce protein largely by taking nitrogen (and carbon dioxide) from the air; the nitrogen is absorbed into the plant via nitrogen-fixing bacteria that live in nodules on the plant’s roots. This provides a sustainable alternative to using nitrogen fertilizer, thus reducing the burden on our soil, waterways and atmosphere. There’s a very strong environmental case that we should get a good amount of our dietary protein from legumes. See, for example, these ethical reviews of Beyond Meat (5/5 Green Stars) and Ripple Milk (4.5/5 Green Stars), both made from pea protein – or the soybean-based staples of tofu and Tofurky (both 5/5 Green Stars). So, is there any justification for removing them from your diet for health reasons?

Why are legumes banned by the Paleo Diet? The image shows six types of legumes in wooden spoons, against a black background.

Why are peas, beans and lentils banned by Paleo?

I’m going to go through every instance of legumes in The Paleo Diet (revised edition, 2011) to see what the problem is, according to Dr. Cordain. Does the book provide any solid arguments to avoid legumes? It was a useful exercise for me as it clarified some issues that I had often wondered about. So, let’s get started…

The Paleo Diet, p. 17: “Consumption of fatty meats and organs had a survival value when humans didn’t eat grains, legumes, dairy products, refined sugars, and salty processed foods, the foods that produce chronic low-level inflammation in our bodies through a variety of physiological mechanisms.

Advice from the Mayo Clinic on reducing inflammation: Eat more plants, including lentils and whole grains, and cut down on red meat. Legumes such as beans and lentils and also whole grains are widely considered to be beneficial for fighting inflammation and all reputable sources (WebMD, The Arthritis Foundation, Scripps, etc.) have the opposite view to Cordain on both meat and legumes. This 2016 review on the anti-inflammatory effects of the Mediterranean Diet (MedDiet) examined many studies and meta-analyses and concluded that the MedDiet reduces the risk of cancer and cardiovascular disease by reducing inflammation. The MedDiet is described as:

Abundant consumption of olive oil and high consumption of fruits, vegetables, cereals (preferably as whole grain), legumes, nuts and seeds. The MedDiet also includes moderate consumption of fish and shellfish, white meat, eggs, and fermented dairy products (cheese and yogurt), as well as relatively small amounts of red meat, processed meats, and foods rich in sugars.

I searched but couldn’t find any studies that indicated that legumes may cause inflammation. If anyone knows of one, please comment below.

The Paleo Diet, p. 19: “Cereals, most dairy products, legumes, meat, fish, salty processed food, and eggs produce net acid loads in the body. By far the worst offenders on this list are the hard cheeses…

Some of these foods generate acid as we digest them, but the extent of acid production differs greatly, particularly when you compare animal products with legumes. A 2011 paper (Schwalfenberg, 2012) looks at the possible benefits of an alkaline diet and contains data on the potential renal acid load of various foods. The acid load ranges from the most acid-generating foods like hard cheeses (parmesan cheese has the highest acid load at 34.2) to alkaline foods like leafy greens (spinach has a negative acid load at −14.0; in other words it is alkaline). The table below lists the acid load for the meats, fish and legumes that were listed in the paper.

Potential renal acid loads of selected foods (Schwalfenberg, 2012)

Food Acid load
Corned beef 13.2
Turkey 9.9
Veal 9.0
Lean beef 7.8
Frankfurters 6.7
Trout, brown 10.8
Cod fillets 7.1
Lentils 3.5
Green beans -3.1

Of the legumes, lentils have a low acid load (3.5) compared to meat and fish, and green beans are actually alkaline (-3.1). Cordain lists legumes after dairy, implying that they are high on an acid-generating list, but in reality legumes are among the most neutral of the major proteins (meat, fish, dairy, and legumes). For the record, whole-wheat bread is also close to neutral (1.8). Here’s a useful video on the subject of dietary acid load and kidney disease.

The Paleo Diet, p. 23: “The paleo diet is simplicity itself. Here are the ground rules:

  1. All the mean meats, fish, and seafood that you can eat.
  2. All the fruits and nonstarchy vegetables that you can eat
  3. No cereals
  4. No legumes
  5. No dairy products
  6. No processed foods

So, he feels strongly enough about legumes that he bans them outright in the Paleo Diet, and this advice is followed religiously by many Paleo Dieters who have taken him at his word. Although, to be fair to Paleo followers, many budding cave-people do debate whether legumes should be allowed.

The Paleo Diet, p. 47: In a section titled Not Enough Protein, he states that protein makes up 15% of the calories in most American diets but he thinks it should be closer to 19 to 35%. He goes on to state that legumes like lentils, peas, and beans average 27% protein. Instead of eating these protein-rich plants he thinks that we should eat more “game meats” that contain up to 83% protein. He makes the statement, “I can assure you that there is no such thing as too much protein,” which conflicts with virtually every scientific study on animal protein intake and longevity. It’s quite funny that he begins a sentence that is categorically wrong with, “I can assure you…” – and he also neglects to back it up with any data. This post on the scientifically-grounded book, Proteinaholic, covers the topic of recommended protein intake, and a recent post on the health-impact of low-carb diets covers the influence of animal protein intake on mortality.

The Paleo Diet, p. 48: “Many whole grains and legumes don’t have a lot of vitamins and minerals.

In response to that, I’ll just refer you to The World’s Healthiest Foods entries for soybeans, black beans, and lentils.

Ibid. “One of the great dietary myths in the Western world is that whole grains and legumes are healthful. The truth is that these foods are marginal at best. But what about the “health-food” breads? At best, they’re less bad than the overprocessed, super-refined white breads…

This is interesting – he throws legumes into the statement but the remainder of the section is dedicated to the dangers of highly-processed white bread. This is a recurring tactic – mentioning legumes in a sentence along with other things (hard cheese, refined sugars, etc.) and then only discussing a non-legume food for the remainder of the passage. News flash: We know that over-processed white bread is not nutritious. News flash #2: White bread doesn’t contain legumes.

Also, he states that “these foods are marginal at best” – even if that was true, that they are only marginal, does this justify banning two major categories of sustainable and healthy foods?

The Paleo Diet, p. 54: “Acid-producing foods are meats, fish, grains, legumes, dairy products, and salt.

See response to p. 19, above.

The Paleo Diet, p. 58: “Other antinutrients, called “phytates,” chemically bind iron, zinc, copper, and calcium within grains and block their absorption during digestion. Pyhtates do their job so well that the worldwide epidemic of iron-deficiency anemia – which affects 1.2 billion people – is universally attributed to the poor availability of iron in cereal- and legume-based diets.

If you take a look at the entries for legumes from The World’s Healthiest Foods that I linked to above, you’ll see that they are all high in iron. Phytates do bind iron, zinc, and other metals besides those listed above, but Cordain is painting a distorted picture of phytates here. They are actually considered to be net positive as they may play an important role in protecting us from damage from toxic heavy metals. Like many issues in nutrition, it’s a matter of finding the right balance. This article provides a balanced overview of phytates so I will refer you to it instead of repeating the information in it. Briefly, here are a few things to consider if you are concerned about phytates:

  • Phytate content is often higher in nuts (e.g., almonds, pecans, and brazil nuts) and seeds (e.g., pumpkin and sesame) than in legumes, so if Cordain was really worried about phytates he would ban nuts and seeds rather than legumes.
  • Phytate content in legumes is reduced considerably during preparation (soaking, germination, fermentation, etc.) so we probably ingest more phytates in the foods that we eat raw (avocado, almonds, etc.) than in legumes.
  • Ultimately, the point here is that phytates are not unique to legumes and, more importantly, they are not considered to be bad for your health.
  • The issue of iron deficiency is linked to poor diet and other causes – vegetarians don’t have a higher incidence of iron deficiency.

Ibid. Few realize that cereal grains and legumes are a catastrophe for your bone health. As with iron and zinc, the little calcium that’s present in whole grains is bound to phytates…

Again he mentioned grains and legumes and then goes on to talk only about grains and milk. The legumes just got tossed in there. Does he ever provide evidence that legumes are bad for bone health? Nope – he only states that “few realize” it. Maybe few realize it because it just isn’t true?! A scientist needs to back up statements with some kind of evidence. For example, most of the relevant studies to date suggest a positive correlation between soy intake and bone health – particularly, reducing the risk of bone fracture in women. More on that topic below.

The Paleo Diet, p. 59: “In many of the world’s undeveloped countries, where whole grains and legumes are the main source of calories, rickets, osteoporosis, and other bone-mineral diseases are common.

Again, this is dreadfully misleading. Implying causality purely based on geographical association is laughable. But even the assertion itself is wrong – bone-mineral diseases are not more common in countries where whole grains and legumes are the main source of calories. For people living in developed countries (i.e., for those who are lucky enough to even have the first-world problem of debating whether the Paleo Diet is worth following), bone-mineral issues most commonly manifest as hip fractures. The incidence of hip fracture is much higher in the US than in Japan, China, and South American countries where grains and legumes (e.g., rice, beans, soy products, etc.) are a larger part of the diet.

The Paleo Diet, p. 71: “When you start the Paleo Diet, you’ll probably realize – perhaps with a shock – how much of your diet has been built around cereal grains, legumes, dairy products, and processed foods.

Actually the legumes constitute one food category that most of us don’t eat enough of. The UN FAO declared 2016 as the Year of the Pulse to encourage more people to grow and eat legumes because of their sustainability and health benefits.

The Paleo Diet, p. 82: “Most vegetarian diets are based on starchy grains and legumes. Sadly – despite continuing perceptions of these as healthy foods – vegetarian diets don’t reduce the risk of cancer.

In the interview that I featured in my previous post on the Paleo Diet, Cordain (about 2 minutes into the video) mentions two papers that he claims show that a vegetarian diet doesn’t reduce the risk of cancer (and heart disease). The papers (published in 1999 and 2009) report on studies published by Prof. Tim Key’s group at the University of Oxford. In his interview, Cordain states that the 1999 study found that a vegetarian diet did not reduce heart disease and that neither study found a difference in cancer rate. The actual conclusion of the 1999 paper: “Vegetarians had a 24% lower mortality from ischemic heart disease than non-vegetarians.” And the 2009 study concluded that “the incidence of all cancers combined was lower among vegetarians than among meat eaters.” So, even the papers that he specifically mentioned actually contradict his statements.

Since then, Prof. Key has been in the news a lot with more recent studies demonstrating that meat intake increases the risk of cancer – here’s a summary from The Guardian of a study published in 2019. There are many other studies that connect meat intake with cancer and heart disease. For example, this systematic review and meta-analysis of mortality from all forms of cancer and cardiovascular disease concluded:

Our results suggest that vegetarians have a significantly lower ischemic heart disease mortality (29%) and overall cancer incidence (18%) than non-vegetarians.

But Cordain goes on to say:

Ibid. However, with the low-glycemic Paleo Diet, which is also high in lean protein and health-promoting fruits and vegetables, your risk of developing many types of cancer may be very much reduced.

Yes, fruit and veg are protective but meat is not – another example of the tactic of slipping in an unsupported idea (in this case, that meat may reduce the risk of cancer). As discussed in the post on low-carb diets, the risk of cancer (and cardiovascular disease) is significantly higher in populations that follow animal-based low-carb diets.

The Paleo Diet, p. 93: “No one knows exactly how viruses, bacteria, and foods can spark <autoimmune diseases> in genetically susceptible people, but research from our laboratory increasingly implicates recently introduced Neolithic foods such as grains, legumes, dairy foods, potatoes, and other members of the nightshade family.

Dr. Cordain had the platform of a book to tell us about them – it’s a shame that he didn’t divulge these findings rather than vaguely hinting about them. Instead of tell using about his research, he goes on to talk about celiac disease, again focusing on grain (gluten) but just slipping the legumes in there even though they are gluten-free and therefore not relevant to celiac disease.

Ibid. “To date, no dietary intervention studies have been conducted to see whether Paleo diets – free of grains, dairy products, and legumes – can reduce the symptoms of these diseases. However, anecdotal reports…

I’ll stop you there with your anecdotal reports. No doubt, some people who cut out processed food and dairy will lose weight and experience an improvement in health. But to claim that exclusion of legumes is part of this, you need evidence.

The Paleo Diet, p. 94: “Legumes and grains contain substances called lectins. These substances are proteins that plants have evolved to ward off insect predators.

This is an entire page that deals with lectins and autoimmune disease. He goes on to talk about leaky guts for a while:

Ibid. “The lectins in wheat (WGA), kidney beans (PHA), soybeans (SBA) and peanuts (PNA) are known to increase intestinal permeability and allow partially digested food proteins and remnants of resident gut bacteria to spill into the bloodstream.

First, lectins are present in most plants. They tend to be more abundant in raw legumes such as beans but it has been known for decades that they are largely removed upon cooking – for example this 1983 study on lectin content in kidney beans found that: “Heating presoaked beans at 100°C for 15 min or at 80°C for 2 hr, or pressure cooking (15 psi) for 45 min without presoaking, decreased the hemagglutinin activity to below detectable levels. Commercially canned beans have lectin levels similar to beans pressure cooked for 30 min.”

This article on legumes provides a useful perspective – the story is similar to that of phytates. The fact is that lectins are present in many foods and are actually considered to be beneficial in the quantities that we encounter in a balanced diet. Here’s a quote from it:

Lectins break down the membranes of hurtful invaders: cancer cells (reducing prostate, colon and other cancers), fungi, bacteria and viruses (even the HIV-1 retrovirus) is part of the reason that tomatoes, corn, whole grain rice, wheat, oats, nuts, sunflower seeds, peaches, mangos, grapes, cinnamon, citrus, berries, tea and most other plant foods are healthy.  All of these contain significant amounts of lectins.

Cordain ends this piece with this call to action:

Ibid. “If you have an autoimmune disease, there is no guarantee that diet will cure it or even reduce your symptoms, but there is virtually no risk, and there are many other benefits from the Paleo Diet that will improve your health.

So he finishes the section on autoimmune disease by making it clear that the diet may not help them, but you should try it anyway because it’s a healthy diet. Again, see the last post for a summary of what’s healthy and unhealthy about the Paleo Diet.

There are a few other mentions of legumes in the diet/recipe section of The Paleo Diet but there are no further arguments on why you should avoid them – he just reiterates that they should be excluded.

Why are legumes banned in the Paleo Diet? The image shows green peas in their pods hanging from a plant.

Legumes increase your lifespan

The ultimate measure of health is lifespan. A key study looked at intake of various food groups around the world and found that there was a 7-8% reduction in mortality hazard ratio for every 20g increase in daily legume intake. This correlation between legume intake and longevity was statistically significant (the P-value was 0.02). The title of the paper said it all: Legumes: the most important dietary predictor of survival in older people of different ethnicities.

This systematic study and meta-analysis, published in 2017, looked at legume intake in 367,000 people and demonstrated that a high legume intake is correlated with a 10% reduction in the risk of cardiovascular disease and stroke.

In summary, I’ve gone through every argument against legumes in The Paleo Diet and in each case the scientific studies refute his unsubstantiated claims. In fact, legumes look more attractive than ever as a dietary staple.

Dr. Cordain bent the Paleo Diet rules by allowing wine consumption (and, coincidentally, had previously received over $150,000 of funding from the wine industry) so why is he so against legumes, which are recognized as healthy by just about everyone? Meat is increasingly being recognized as unhealthy and unsustainable and legumes are the major alternative to meat as a dietary protein source. Is there some kind of agenda, other than health, at play here?

13 thoughts on “Why are legumes banned by the Paleo Diet?

    1. That’s supposed to be part of it but even if you accepted that strange and arbitrary way of deciding on a diet, the author’s vision of the caveman diet is not based on solid science. Paleo people ate a wide variety of plants, including legumes, according to remains excavated.

      1. Yeah, but it’s the “image” thing. Can’t have a caveman, club in hand, eating a burrito, now can we. I never understood how the paleo folks ever thought excess protein couldn’t hurt you. Doesn’t take a rocket scientist to look at excess protein and kidney issues, and gout. You can go back to 17th Century literature, look at the diet of the upper classes, and the “diseases of kings.”

  1. Completely agree. Unless there is a special medical reason, I just don’t see why legumes need to be excluded from a general healthy diet. It is so frustrating to me that both Paleo and the popular Whole30 diet exclude them; it’s silly both from an environmental AND nutrition reasons -_-

    1. Hey Lara,
      Thanks for your comment. I actually did a post-doctoral project on early detection of food-spoilage fungi (especially those that produce mycotoxins such as aflatoxin).
      This review on the incidence of aflatoxin says this: Commodities such as corn, peanuts, pistachio, Brazil nuts, copra, and coconut are highly prone to contamination by aflatoxin, whereas wheat, oats, millet, barley, rice, cassava, soybeans, beans, pulses, and sorghum are usually resistant to aflatoxin contamination.
      So, most legumes don’t pose a significant risk for aflatoxin, except for peanuts. The main concern is when you eat products that are processed to some extent (where it’s more difficult to see, smell, or taste that the food was spoiled before it was processed) – so if you eat peanut butter, for example, I think it’s important to buy a brand that you trust, that will have good quality control.
      Besides processed food, another route for aflatoxins to humans is in milk or meat from animals that were fed with spoiled feed.

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