Dr. Oz did a segment on Paleo last year with Nell Stephenson and Dr. Loren Cordain, and it got great ratings. However, the feedback the show received from their viewers was that “The Paleo Diet” as presented by Nell and Dr. Cordain was too restrictive. The producers invited me on because I consider Paleo to be more of a template than a rigid prescription, and my approach doesn’t prohibit foods that aren’t typically considered to be “Paleo”—such as full-fat dairy, white potatoes, dark chocolate, and legumes.
Some people—particularly those not previously familiar with my work—were surprised to hear me tell Dr. Oz that I think eating a few servings of legumes a week is fine as long you tolerate them well. This directly contradicts Paleo dogma on legumes, which holds that we should strictly avoid them because 1) they aren’t part of our ancestral diet, and 2) they contain toxic anti-nutrients like lectin and phytic acid.
But are these arguments supported by the evidence? Let’s find out.
Legumes: More #Paleo than you might think!
Back in November of 2013, Dr. Stephan Guyenet posted an article outlining the evolutionary history of legume consumption. He demonstrates that, contrary to popular belief, legumes were part of our ancestral diet. Recent analysis of Neanderthal tooth plaque revealed that they consumed wild varieties of peas and fava beans. (1) Since early humans are thought to have eaten a more diverse diet than Neanderthals, it is safe to assume that our human ancestors also ate legumes.
Dr. Guyenet also points to several contemporary hunter-gatherer groups that consumed significant amounts of legumes, including the !Kung San of the Kalahari desert (who relied heavily on a legume called the tsin bean) and the Australian Aborigines (who extensively harvested the seeds and gum of Acacia trees, another legume).
This research suggests that legumes are, in fact, “Paleo”. But even if Paleolithic people didn’t eat legumes, is that reason enough to avoid them? If it is, then shouldn’t we also strictly avoid dark chocolate, coffee, green tea, and alcohol? What about the glut of breads, muffins, packaged snacks, desserts, and even candy (no, I’m not kidding) claiming to be “Paleo” that have recently become so popular? It should be obvious that our ancestors were not baking with nut flour, chowing down on truffles or drinking “Paleo” cocktails. Yet even the most die-hard, self-identified Paleo purists typically consume at least some of these foods and beverages, and don’t seem to see a contradiction in that. Why should legumes be any different?
As I’ve argued before, Paleo is best viewed as a template or a starting place,—not an inflexible, unchanging system based on (sometimes mistaken) beliefs about what our ancestors ate. Mark Sisson said something very similar in a recent blog post:
The anthropological record is a framework for further examination of nutritional science; it does not prescribe a diet.
A more important question to ask than whether a food is “Paleo” is how it impacts human health. Fortunately, in the case of legumes, we have a lot of modern research that can help us to answer that question.
Should we avoid legumes because of the anti-nutrients they contain?
Paleo dogma on legumes holds that we should avoid them because they contain toxic anti-nutrients called lectins and phytic acid (aka phytate). Let’s take a look at each of these compounds in legumes and see if this argument holds up.
Lectins are a type of protein that can bind to cell membranes. Studies have shown that lectins can impair growth, damage the lining of the small intestine, destroy skeletal muscle, and interfere with the function of the pancreas. Sounds serious, right?
Not so fast. There are several reasons that these results cannot be extrapolated to humans. First, the animals consumed very large amounts of lectins—much larger than a human would get from a varied diet which includes legumes. Second, the lectins were from raw legumes. Why is this significant? Because humans eat primarily cooked legumes, and cooking neutralizes the lectins found in most legumes.
In fact, cooking legumes for as little as 15 minutes or pressure-cooking them for 7.5 minutes almost completely inactivates the lectins they contain, leaving no residual lectin activity in properly cooked legumes. (2)
What’s more, other components in food (e.g. simple sugars) can bind to lectins and diminish their toxic effect. So even if there is a small amount of lectin left after cooking, it’s unlikely that it will have a detrimental effect given the presence of simple carbohydrates in legumes that can bind to the proteins. (3)
Finally, if lectins really are a problem then we’ll have to cut out a lot more than legumes from our diet in order to avoid them. It turns out that lectins are present in at least 53 fruits, vegetables, spices and other commonly eaten plants, including carrots, zucchini, melon, grapes, cherries, raspberries, blackberries, garlic and mushrooms—to name a few. (4)
This is not an invitation to stop eating these foods! It’s simply a reminder that almost every plant we eat contains small amounts of toxins, since this is how plants defend themselves. In the majority of cases these low levels of toxins don’t harm us, and in fact, they may even provide health benefits. For example, many of the compounds we call “antioxidants”—like polyphenols found in blueberries, dark chocolate, etc.—are actually “pro-oxidants” that cause mild oxidative stress and thus upregulate our body’s natural defense systems. (5)
To my knowledge there’s only one study demonstrating humans being harmed by consuming legumes. This is the study often used by Paleo advocates to “prove” that legumes are dangerous. However, what is often neglected is that this study described a case of food poisoning that occurred in hospital patients who ate legumes that hadn’t been cooked properly. (6) Suggesting that we shouldn’t eat cooked legumes because raw legumes cause disease is like saying that we shouldn’t eat cooked chicken because we can get Salmonella from eating raw chicken.
The one lectin we may want to exercise caution with is peanut lectin, since both raw peanuts and peanut oil have relatively high lectin content. Some data in animals suggest that peanut lectin may contribute to atherosclerosis by stimulating the growth of smooth muscle and pulmonary arterial cells. (7) However, other research (including clinical trials) in both animals and humans have found that peanuts and even peanut oil reduce cardiovascular risk factors and thus may protect against heart disease. (8, 9) In light of this conflicting data, and because of other risks associated with peanut consumption such as exposure to aflatoxin, I recommend either minimizing your intake of peanuts or avoiding them entirely.
Phytic acid (aka phytate)
Phytic acid is the storage form of phosphorus found in many plants, especially in the bran or hull of grains and in nuts and seeds. Although herbivores like cows and sheep can digest phytic acid, humans can’t. This is bad news because phytic acid binds to minerals (especially iron and zinc) in food and prevents us from absorbing them. (It’s important to note that phytic acid does not leach minerals that are already stored in the body; it only inhibits the absorption of minerals from food in which phytic acid is present.)
Phytic acid interferes with enzymes we need to digest our food, including pepsin, which is needed for the breakdown of proteins in the stomach, and amylase, which is required for the breakdown of starch. Phytic acid also inhibits the enzyme trypsin, which is needed for protein digestion in the small intestine.
Sounds pretty bad, right? While it is true that diets high in phytic acid contribute to mineral deficiencies, it’s also true that humans can tolerate moderate amounts of it without harm (perhaps because our gut bacteria produce enzymes that break down phytate and extract the nutrients the body needs). In fact, there’s even evidence that phytic acid may have some beneficial effects. It prevents the formation of free radicals (making it an antioxidant), prevents the accumulation of heavy metals in the body, and plays a role in cellular communication.
The problem with telling people to avoid legumes because they contain phytic acid is that many other foods in the diet—including “Paleo-friendly” foods—contain substantially higher amounts of phytic acid than legumes. For example, a serving of trail mix, that beloved Paleo favorite, is likely to be much higher in phytic acid than a serving of lentils. Cacao beans (chocolate) have about the same amount of phytic acid as most beans. And spinach and swiss chard are higher in phytic acid than almost any legume, nut or seed!
|·Food· ·||Phytic acid (mg/100 grams)·|
I know some of you will be tempted to stop eating spinach and Swiss chard after seeing this chart. That’s not the point! Remember, the dose makes the poison. High levels of phytic acid are harmful, but moderate amounts within the context of a diet that is nutrient-dense overall are not. Moreover, phytic acid only binds to certain minerals and prevents their absorption. There are many other nutrients in spinach, Swiss chard, and all other foods containing phytic acid that will still be absorbed when you eat them.
It’s also important to note that phytic acid can often be at least partly broken down by certain food processing methods, such as soaking and roasting. I wrote an article a while back called “Another Reason Not To Go Nuts on Nuts” suggesting that you soak and then dehydrate or roast nuts before eating them for exactly this reason. In the case of legumes, studies have shown that soaking at room temperature for 18 hours or at 140 F for 3 hours eliminates between 30–70 percent of phytic acid—depending on the legume. (13)
The takeaway is this: phytic acid in legumes is not a cause for concern as long as you’re eating them in moderation and they aren’t displacing more nutrient-dense foods from your diet. This is especially true if you are soaking legumes prior to consuming them.
Are there any reasons we might want to limit legumes in our diet?
If you’ve read this far, you might think I’m a big advocate of legumes. That’s not the case. While they do contain beneficial nutrients and fiber (which feeds the gut flora), they are not as nutrient-dense as other Paleo foods—like organ meats, meats, fish, shellfish, eggs and vegetables—and, as I mentioned above, some of the nutrients they contain are not bioavailable due to phytic acid. (14) Because maximizing nutrient-density is one of the most important things we can do to improve our health, I think it makes sense to limit consumption of legumes to a few times a week, and to prepare them properly (i.e. soak for 18 hours and cook thoroughly) when you do eat them.
Another reason some people may need to avoid legumes is that they contain FODMAPs, which are carbohydrates that are poorly absorbed by some people and can cause gas, bloating, and other digestive symptoms.
You probably remember this song from when you were a kid:
“Beans, beans, the magical fruit, the more you eat, the more you toot…”
FODMAPs are probably the main reason beans have this effect on some people. But not everyone is sensitive to FODMAPs, so this isn’t a reason to avoid legumes across the board. That’s like saying that everyone should avoid shellfish because some people are allergic to them.
Final thoughts and a caution about Paleo dogma
Legumes are not necessary for human health. They contain no nutrients that we can’t get from other foods—often with less trouble (i.e. no need to go through extensive preparation methods to make the nutrients more bioavailable).
That said, if you enjoy them, tolerate them well, and are willing to prepare them properly, there is no credible evidence showing that they will harm you when eaten in moderation in the context of a nutrient-dense diet—regardless of whether they are “Paleo”. The same can be said for many other “grey area” foods that are popular in the Paleo community, such as dark chocolate, alcohol, nut flour, and full-fat dairy (like butter and ghee).
I’ve recently been criticized on social media by some defenders of “The Paleo Diet” for my comments about legumes on the Dr. Oz segment. They insist that legumes are “not Paleo” and that they cause harm. When I ask them for proof of these claims, they almost exclusively point to Dr. Loren Cordain’s work. Dr. Cordain wrote the first mass market book on Paleo nutrition and has published many scientific papers on the subject, most of which I have read. I have great respect for his contribution.
But the idea that a single authority is uniquely capable of interpreting the research on a topic as diverse as Paleolithic nutrition, and that their opinion is infallible and unassailable, is dogma—not science. The Merriam Webster dictionary defines dogma as “a belief or set of beliefs that is accepted by the members of a group without being questioned or doubted.” Google dictionary defines it as “a principle or set of principles laid down by an authority as incontrovertibly true.”
I feel strongly that we need to guard against this, both for our own benefit and if we want Paleo to be taken seriously in the scientific community and mainstream medical establishment. We should always be ready to question even our most cherished beliefs, and prepared to change our minds in the face of new evidence. And it’s imperative that we apply the same standards of critical thinking to Paleo arguments that we do to conventional arguments.
I’m by no means perfect in this regard. I’ve had blinders on in the past about certain issues (my stance on fructose and naturally-occurring omega-6 fats in foods like avocados come to mind), I’m sure I have blind spots now, and I won’t be immune to them in the future. Unfortunately, the tendency to succumb to groupthink seems to be a hardwired part of human nature. As clinicians, researchers, and scientists, all we can do is strive to be more rigorous and consistent in our thinking, and support each other in that process.