No matter where you fall on the dietary spectrum, legumes (soy, beans, peas, lentils, peanuts etc.) are some of the most hotly debated foods on anyone’s plate. We’re all familiar with vegetarian and vegan diets that swear by legumes as a superior substitute for animal protein. But aside from those with edible pods, legumes are eliminated on the Paleo diet. What does research show us about legumes—and why do we exclude most of these foods from a nutrient-dense diet?
Today, I’m going to bust three of the most common myths about legumes using (you guessed it) science!
Myth 1: Beans (legumes) are a good source of carbohydrates, especially for diabetics.
While it is true that beans have a high concentration of slow-burning carbohydrates, the the same compounds that ensure the carbohydrates in legumes hit our bloodstreams gradually (a boon for blood sugar regulation) can also contribute to increased intestinal permeability, or what most of us call “leaky gut”.
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A leaky gut occurs when the cells that for the lining of the small intestine (called enterocytes), or the proteins that bind them all together, become damaged or altered. This allows incompletely digested proteins, bacteria from your gut, and wastes that would otherwise be excreted to leak through the microscopic holes in your intestinal wall, causing the immune system to mount a response against these tiny intruders (see What Is a Leaky Gut (And How Can It Cause So Many Health Issues)?). As the problem gets more severe, the immune system stops being able to contain it, and inflammation can become body-wide in addition to toxins from the gut getting into the bloodstream. As I discuss in detail in The Paleo Approach, leaky gut is a major contributor to autoimmune disease.
Beans are recommended as a good source of carbohydrates for diabetics, because, when they are digested, saponins are released. Saponins exist in some quantities in all plants and are a source of defense for plants to fight against invasion and infection from microorganisms as well as insects. In the gut, they embed within the enterocyte cell membranes to create crater-like pores (see How Do Grains, Legumes and Dairy Cause a Leaky Gut? Part 2: Saponins and Protease Inhibitors). These pores inhibit the transport of sugars across the cell and into the body by interfering with the sugar transporter proteins in the cell membrane. From a nutritional perspective, the net effect of the saponin pores are that carbohydrates are absorbed more slowly, making legumes a “low glycemic index” source of carbs. Thus, the slower transport of sugar into the bloodstream has been perceived as a benefit for years. However, when there are too many saponin pores in a cell membrane (or those pores are too large or very stable), the cell can actually die (via a mechanism called apoptosis) and this can lead to leaky gut.
Legumes also contain a type of problematic lectin called agglutinins (see Are all lectins bad? (and what are lectins, anyway?) and Why Grains Are Bad–Part 1, Lectins and the Gut). Agglutinins affect the type of bacteria that like to grow in our guts in a negative way, typically preferentially overfeeding certain undesirable strains like E. coli. There are three known mechanisms through which agglutinins can enter the body (which appear to be independent of genetics, although more studies are required) where they are known to stimulate the immune system in a big way. Plus, agglutinins can damage enterocytes as they enter the body, contributing to a leaky gut. There’s definitely a spectrum here, some agglutinins are worse that others, and some are deactivated by soaking and prolonged cooking, but overall, consuming beans and other legumes for their carbohydrates isn’t worth the damage done to our gust!
Myth 2: Legumes are a great source of protein.
In one sense, it’s easy to understand how legumes became such a staple in vegan and vegetarian diets. When people following these diets eliminate meat, they are suddenly faced with the challenge of replacing the protein that they would have gotten from animal products. Thanks to decades of misinformation, legumes, especially the soaked and sprouted variety, are frequently recommended not only as a solution to an otherwise protein-deficient diet but as a quality protein for everyone! However, even though soaking and sprouting legumes does make the protein in them more bioavailable and easier to digest, that doesn’t mean they actually contain the right types of protein (see Plant-Based Protein: What is its Role in the Paleo Diet?).
The proteins found in legumes are not (with a couple of exceptions) complete proteins, meaning that they do not contain all of the essential amino acids that humans need to function optimally. Plus, plant proteins are harder for our bodies to digest and use and have lower Digestible Indispensable Amino Acid Scores than animal proteins. This, combined with the low protein density of legumes (especially if you were to compare them to an animal protein source; you typically get 3g of carbs for every 1g of protein in legumes, at best) makes them an inferior source of protein. For those who prefer to follow a vegetarian version of the Paleo diet, I encourage both the consumption of eggs and high-quality grass-fed dairy (if tolerated) as well as considering a pescetarian Paleo diet (one that includes fish) as an alternative.
Myth 3: All legumes are bad.
“But wait,” you cry—”what about legumes with edible pods? What about green beans and snow peas?” Unlike their bean-ier cousins, legumes with edible pods have a relatively low agglutinin content and tend to contain agglutinins that are more completely and easily deactivated by heat (i.e., cooking). So, simply steaming these types of legumes should be enough to render them nearly harmless. They also tend to have low concentrations of phytates compared to other legumes, another potentially gut-irritating compound. Combined with some compelling nutrition contained in the pod (including, vitamins, minerals, fiber and phytonutrients), the scale starts to tip in the other direction (see The Green Bean Controversy and Pea-Gate).
Each type of legume contains different amounts and types of agglutinins, saponins and other antinutrients. And while it’s certainly true that some are more harmful than others and that cooking (especially traditional cooking techniques that involve soaking, sprouting, fermenting and/or prolonged cooking) can greatly reduce the activity of these compounds, so far there are no comprehensive studies detailing the 
amounts of each lectin in the various types of legumes (surprising, right?) nor how to best prepare each type of legume to render them safe and maximize their nutritive value). Until the science can provide us with these details, the Paleo diet omits all legumes with the exception of those with edible pods due to their unique nutrient profile. And, just as is the case with gluten-containing foods, there aren’t any nutrients within legumes that we can’t get more and better from quality meats, seafood, vegetables, fruit, eggs nuts and seeds.
Citations
Essentials of Glycobiology. Chapter 30 (Plant Lectins) Varki A, Cummings R, Esko J, et al., editors. Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 1999. http://www.ncbi.nlm.nih.gov/books/NBK20717/
Messina MJ. Legumes and soybeans: overview of their nutritional profiles and health effects. Am J Clin Nutr. 1999 Sep;70(3 Suppl):439S-450S.
Vasconcelos IM, Oliveira JT. Antinutritional properties of plant lectins. Toxicon. 2004 Sep 15;44(4):385-403. http://www.ncbi.nlm.nih.gov/pubmed/15302522
Mechanisms of interaction with the gut barrier and the immune system are summarized with dozens of references in The Paleo Approach.
Paleo Conversations: Jennifer Robins
Dear Sarah,
I love science and your articles are always well researched and very educational. Yet, when it comes to pulses, it is hard to disregard the fact that – for instance – Ikarians for whom pulses are a large part of diet, are also one of the longest living and healthiest populations on earth (one amongst many). Science or long standing, healthy culture? Why there is this rather obvious discrepancy?
I have a question…what about edemame, with or without the pods?
Edamame is soy, and Sarah does not recommend soy. -Kiersten
Yes. This was my concern. Science research shows legumes linked to the healthiest people on earth. Increased longevity as well.
I believe the Paleo community has crafted too many false dichotomies with respect to anti-nutrients. Even phytic acid (in reasonable quantities) has beneficial effects.
I think you should add saponins to the list of leniencies (along with some lectins & legumes) as they are the molecules responsible for the therapeutic effects of ginseng and various other medicinal herbs.
Given that, as with anything, some are good, some are bad, all in moderation etc., shouldn’t we reserve judgement on legumes for whatever epidemiological data has to offer? Where is the evidence that leaky gut is a result of legume consumption? When I look for such evidence, all I seem to find is the wonders of legumes for gut flora by why of resistant starch etc.
You say legumes aren’t good sources of protein, yet this is latest message about muscle meats. In fact, legumes score low in the amino acid methionine, which is plausibly the most harmful amino acid.
I don’t think we need to compare the two, yet a fairer comparison will reveal that legumes have less methionine, more resistant starch, are more sustainably produced and at a fraction of the cost of meat.
Doesn’t soaking overnight reduce the anti-nutrients to a safe level? As you said all plants contain saponins to a certain level so who’s to say after soaking and cooking legumes aren’t as safe as many other plants that are allowed on the Paleo diet?
Yes, soaking does reduce the anti-nutrients, but to what extent depends on the legume. Some people still don’t tolerate legumes even once they have been soaked, sprouted, fermented, etc. -Kiersten
Would love to hear the answer to that Beata!!! I often wonder the same thing.
HI Sarah, I had a read of the article and sorry to say its close to the biggest load of rubbish I have read in a long time. There is no science in this article and the rational is floored. I find this with lots of Paleo information for some reason. The concept of legumes creating leaky gut just does not make sense and is pure hypothesis. Saponins dont cause crater holes in the gut. Its just ridiculous. The idea that they damage gut ecology is actually the complete opposite. You focuses on one compontent agglutins but the butryic acid produced by legumes have a hugely positive impact on GUT ecology and healthy bacteria feed on this substance which actually heals the gut. We already know that legumes are not a complete protein and have known this for years so this is why we combine legumes with nuts and seeds or grains to gain a complete protein. But the body does not have to have a complete protein in one meal. It gathers amino acids from many sources over time and builds complete proteins in the body. The reality is legumes need to be cooked and/or soaked. Soy should be fermented as well rather than eaten as a straight legume. To remove legumes from the diet is just crazy for gut health and as a wonderful source of nutrients, fibre, slow release carbs and some protein. Just look at a billion Indians for centuries have been pure veg and survived and flourished on legumes. The only thing I can think with Paleo is the meat boards are pushing or funding all this rubbish sensationalism. I dont usually comment like this but when I see clear false science I have to make it clear. (there is no link to science in this article, its all hypothesis.) GM legumes should be avoided but thats the same with all GM foods.
Hi Sarah,
Thank you for your wonderful blog. I’ve been following a mostly Paleo diet for several years. In that time, I’ve experienced effortless weight loss, improved immunity, skin conditions going into remission, better sleep, better energy and improved overall health. But I never did eliminate legumes. Recently, I was reading in National Geographic about the “Blue Zones”, places around the world where people are living long, healthy lives. (Ikaria, Greece, as mentioned by another commenter is one of them.) A common thread in the diets of the people in these regions is that they all eat legumes as a staple. (Most of them do also eat meat, but not a lot of it.) The diets in these regions are all different from each other. And none of the diets is Paleo. I’d be very interested to read a blog post from you about these Blue Zones. Why do you think these people are living such long, vibrant lives?
I agree with Jean, I would love to see a well-thought out response from someone in the Paleo community that addresses the many strong, healthy cultures around the world and looking honestly at how they eat…that is way more convincing than a few recent hypothetical studies in a science lab!
Sorry! I will stick to my legumes, nuts and seeds for my protein. I was guided to “stop eating flesh” and will continue to do so.
This article is so full of incorrect information, it must be deleted from the internet so the next generation will not vomit. On a side note plant based protein is much easier to digest than animal protein.