Thursday, November 7, 2013

Lectins and Leaky Gut Syndrome: Good Reason To Give Up Grains and Legumes or Just Another Exaggerated Food Fear?

I’m not a big fan of food fear-mongering or diet extremes, so when I see foods that can play a part in a healthy diet get thrown under the bus (usually for dubious reasons, at best), my skin bristles a little. Of late, I’ve been challenged with the assertion that whole grains and legumes should not be eaten for various reasons, one of those being that they contain anti-nutrients. What inevitably follows in these anti-grain and legume diatribes is that one particular anti-nutrient, lectin, is especially insidious and causes a condition called “leaky gut syndrome.” Consequently, the opinion is that lectin-containing foods such as whole grains and legumes should be avoided.

“Legumes = lectins = leaky gut = leaky brain. I’ll get my carbs and protein elsewhere.”

I shared this quote from an individual I encountered in another post, and I’ve included it again here because I think it’s the perfect example of the true fear and confusion that exists surrounding whole grain, legume, and lectin consumption. Not surprisingly, the individual quoted above closely adheres to the Paleo diet, and it has been my observation that much of the popular anti-grain and legume sentiments generate within this community, as well as in the general low-carbing crowd. These two dietary sects renounce grains and legumes (yet interestingly enough make Paleo Cupcakes and Primal Cookies on the weekend!), but I won’t expound upon the virtuous or faulty aspects of these diets in this post—as always, eat whatever diet suits your health best (though I can’t emphasize enough the value of true dietary balance, eating primarily whole and real foods, and aligning your intake with your caloric needs), but before you banish a food from your eating repertoire, be sure you have all the facts and aren’t eliminating something on unfounded fear.

So are lectin-containing foods such as whole grains and legumes as dangerous to our health as proponents of certain diets purport? Do they really cause the terrible-sounding leaky gut syndrome? While this post won’t be a completely comprehensive discussion of lectins (I do want you to read this, after all), my hope is that I can help provide factual information, clear up some confusion, and, with any luck, silence the hysteria.

What are lectins?

Lectins are carbohydrate-binding proteins found in most plants as well as in dairy. Plant lectins are most abundant in plant seeds but are also found in other tissues such as roots, leaves, bark, flowers, or bulbs. It has been surmised that lectins play a defensive role in plants by protecting the plant against attacks from microorganisms, pests, and insects. As an example of this mechanism, it has been noted that an infection or wounding of a plant increases lectin concentration. Within animals, lectins facilitate cell-to-cell contact, which, as will be discussed later, can prove both positive and negative.

Lectins are found in a wide range of commonly-consumed foods such as tomatoes, beans, peas, wheat germ, rice, corn, garlic, avocado, leek, cabbage, tea, parsley, oregano, spices, bean sprouts, carrots, green beans, white mushrooms, cantaloupe, cherries, raspberries, blackberries, and roasted peanuts. From this listing, it is clear that exposure to lectins is a frequent occurrence for most people.

What are lectins capable of doing in the body?

In high doses, lectins can indeed be toxic. Consider the fairly well-known example of red kidney beans, which can cause a type of “food poisoning” (with resultant vomiting, cramping, and diarrhea) if consumed in the raw state or if improperly prepared.

In animals injected with high levels of lectins, a variety of suboptimal health occurrences have been observed. For example, absorbed lectins can impact distant organs, promoting such conditions as pancreatic growth or atrophy of the thymus.

When given to experimental animals orally, high levels of lectins can interact with gastrointestinal mucosa, triggering acute GI distress symptoms (as in the case with raw red kidney beans), as well as other negative effects. Because lectins have a high resistance to proteolysis and are stable over a wide pH range, they can survive the acidic, enzyme-containing stomach and therefore make the entire journey from mouth to colon mostly intact and biologically active. This has been made clear with the finding of intact lectins in human feces.

Since lectins do survive digestion and are uniquely capable of binding to cell receptors on the gut wall and elsewhere, our bodies may produce antibodies to them or, on the other hand, may induce tolerance. If the body’s defenses do gear up to attack the “invading” substances, a more widespread immune response can result. This has led to speculation that lectins could be involved in autoimmune diseases such as type 1 diabetes or rheumatoid arthritis.

With a substantial proportion of the lectin molecule intact in the gut, lectins are able to bind to cells lining the digestive tract, which can lead to direct membrane damage or can indirectly affect intestinal bacterial flora. In the case of the former, the reaction between lectins and cell membranes is believed to alter cell function in one way or another, producing adverse effects. For instance, the binding of lectins to liver cells in diabetic rats appears to contribute to clumping, deformity, or permeability of cells.

Binding of lectins to gut epithelium can also lead to brush border disruption, perpetuating a reduced absorption of nutrients secondary to a decreased absorptive surface area.

There is also word floating around that lectins from legumes are causing obesity, by means of leptin (a hormone which regulates food intake and body weight) resistance; however, the only available information I found on this was one medical hypothesis presentation (not a study). 

Equally as important to point out when discussing lectin activity is that lectins may just as easily arrive in the gut intact and NOT bind to mucosa, in which case there is typically little or no harmful effect induced. What corresponding factors must be present for lectin-induced damage to occur is still not clear, though lectin studies with rodents done to date have provided some more insight.
It’s not clear in what circumstances ingested lectins cause damage

In experimental rodents, lectin activity and the potential for subsequent toxicity is influenced by the degree and type of bacterial growth in the intestine, and studies suggest that certain microorganisims in the gut may even be lectin-facilitating.

Another observation from a study of excised rat GI tract segments treated with lectins points to the idea that lectins may only prove toxic when GI tract cells have been exposed to prior mechanical stress, as lectins can potently block repair, thus increasing membrane disruption. 

As with most any dietary element, dose and context seem to make a huge difference in regards to lectins, and I feel it is crucial to insert a reminder here that the amount of lectin necessary to produce most of the adverse effects seen in rodent studies is significantly higher than the amount that would be consumed in a typical human diet.

The mechanistic factors which dictate the fate of ingested lectin are not completely understood. Whether lectins will cause harm may be dependent on the overall diet history and composition of the diet, as well as the condition of the gut flora, among other factors. Research is still ongoing to determine both the dose and the environment in which lectins produce unfavorable outcomes

Leaky gut syndrome and...lectins?

As alluded to in the introductory section, lectins in whole grains and legumes are often cited as being causative agents of a Loch Ness Monster-esque condition called leaky gut syndrome. Because fear of developing leaky gut syndrome often lends itself to the avoidance of whole grains and legumes, I thought it would be wise to dig into what we know about the leaky gut syndrome phenomenon and separate the fact from the flimsy extrapolation.

What is leaky gut syndrome? While not officially recognized yet in the medical community, leaky gut syndrome is said to encompass a wide range of symptoms including gas, bloating, sensitivities to foods, cramps, skin conditions (eczema, hives, psoriasis), as well as aches and pains. Additionally, leaky gut syndrome has been blamed for a variety of disorders including chronic fatigue syndrome, fibromyalgia, allergies, and depression. It isn’t clear how many people claim to have this condition.

In reality, leaky gut syndrome is still a medical mystery—a very gray area—to doctors, who ascertain that presentation of leaky gut syndrome symptoms usually indicates that there is another diagnosis that needs to be made.

What causes leaky gut syndrome? The proposed theory is that increased intestinal permeability secondary to damage of the intestinal lining, leads to this condition. It is further surmised that a compromised intestinal barrier then lends noxious contents (bacteria, incompletely digested proteins, etc) access to various internal sites and circulation, potentially triggering an autoimmune reaction.

As might be expected, lectins are often too easily implicated by some as causing leaky gut syndrome, since they do have the ability in some cases to cause intestinal damage; however, this allegation of cause-and-effect is merely inference and has not been proven.
Even in more well-known disease conditions such as inflammatory bowel disease (IBD), Crohn’s disease, celiac disease, and irritable bowel syndrome (IBS), the question remains as to whether a compromised intestinal barrier is part of the cause of disease, or is the resulting effect. To date, studies investigating associations between a leaky gut and certain disease states have only been correlative.

Since both human and mouse studies indicate that intestinal barrier loss alone, regardless of cause, does not necessitate disease in otherwise healthy people, it’s not certain what could or should be done with someone who presents with increased intestinal permeability in the absence of other diseases such as IBD or Crohn’s disease. Also, it’s pertinent to point out that all intestinal permeability is not bad, as permeability confers functions such as supporting nutrient and water absorption. 

As of right now, evidence for how to best medically treat leaky gut syndrome is not there—so be warned of anyone who professes to have such an answer. Some alternative medicine practitioners claim that restoring gut barriers will cure underlying disease, but this has not been proven in clinical studies. Additionally, some of these same practitioners are recommending unsubstantiated dietary supplements to cure leaky gut syndrome, so hang on tightly to your wallet.

Now, if symptoms ascribed to leaky gut syndrome are, in fact, being caused by Crohn’s or celiac disease, for example, treating these conditions should resolve the issue. Of course, it is important to consult with your physician—digestive disorders are no joke, and appropriate treatment often resides outside of mere diet modifications.

Should you be concerned about lectins from normal consumption?

The lectins consumed in normal human diets do not seem to be harmful. As evidenced by the many people who eat and tolerate them, the majority of lectins ingested by humans appear to reach the gut without provocation, or if they do interact, do so in a harmless or even beneficial way. As previously mentioned, much of the research done with lectins involves artificially high doses, which do not correspond to typical human intakes. More research is needed to determine what effect lectins have at normally-consumed levels in the human diet, as there have been zero long-term studies in healthy individuals examining the effects of this.

Moreover, while there’s a lot of noise about the potential downsides of lectins, they can be beneficial, too. The body uses lectins for cell-to-cell adherence, inflammatory modulation, and programmed cell death. There may also be supplementary advantageous uses for lectins at non-toxic doses, with research being carried out in the areas of gut regrowth following total parenteral nutrition as well as in anti-cancer therapies.

Additional thoughts and tips before we conclude

Since the following assertion is inescapable in discussions pertaining to eating whole grains and legumes, lectins, and leaky gut syndrome, I might as well throw in my two cents now. I’m pretty sure some of you are thinking, “But we weren’t meant to eat grains or legumes! The toxins and anti-nutrients they contain are proof that they don’t WANT to be eaten!” From an evolutionary standpoint, we may very well not yet be fully adapted to eating grains and legumes. Keep in mind that at some point, humans weren’t adapted to (and many still aren’t) drinking lactose-containing milk from other mammals, but that doesn’t make milk a non-nutritious food that definitively needs to be avoided. 

Furthermore, it’s my view that we weren’t “meant” to do a lot of things that we do today (were you meant to be reading this post on your iPhone in an airplane at 50,000 feet above the earth? was the human body meant to sit on its butt at a desk job everyday? were we meant to eat fatty grain-fed feedlot meat? were people living in the northern latitudes of Minnesota meant to be slathering coconut oil on every morsel of food that touches their lips?), yet we do, because we now live in 2013, not in the Paleolithic era

And as for grains and legumes not wanting to be eaten—please show me an animal that wants to be eaten and maybe I’ll reconsider that argument. Anyway, my take here is that we have these food sources available, they can be a nutritious part of a healthy diet, and are enjoyable to eat, so why not?

Additionally, what Paleo diet proponents and others who shun grains and legumes frequently overlook is the fact that traditional processing of these foods greatly reduce or eliminate lectins. Soaking, fermenting, sprouting, and cooking grains and legumes are all techniques that will deactivate, thereby decreasing, lectins. While fermentation and sprouting generally destroy lectins more efficiently, the two most common techniques for whole grain and legume processing, soaking followed by cooking, will also degrade a good proportion of lectins. Raw red kidney beans can contain up to 70,000 lectin (hemagglutinating) units but through overnight soaking and proper cooking (boiling for at least 10 minutes), lectins can be reduced to safe levels. It is estimated that fully cooked beans contain around 300 lectin units.

My conclusions

With the evidence available at this time, the mere presence of lectins found in plant foods should not be used as a reason to avoid whole grains and legumes. In the many studies I read on this topic, despite potential negative actions of lectin, the consensus among researchers is that ingestion of lectin at levels after processing is unlikely to pose a risk to human health in otherwise healthy individuals.

While there is plenty of scientific literature (largely in observational but also in controlled studies) associating legume and whole grain consumption with health benefits, what is reliably missing, is research showing detrimental effects of normal consumption of whole grains and legumes. Though it is observational, it’s still valuable to mention that diets in the “Blue Zones,” where some of the longest-living people reside, are very plant-heavy—including beans and grains as a staple.

I see no reason to avoid whole grains or beans based on the potential of lectins to cause harm, or the very elusive possibility of getting the even more elusive leaky gut syndrome, if you are able to tolerate these foods and enjoy them. Diets that prohibit whole grain and legume intake without substantive evidence to do so seem absurd.


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  1. Great article! Love to see another person in the profession going through the research on this. Seen several RDs and nutritionists spouting about leaky gut as if its fact. Also, love to see another nutrition blogger who uses citations!

    1. Thanks for the comment Kevin! Glad you enjoyed the post. Like you, I felt there was far too much misinformation being spouted out there about lectins and leaky gut and needed to do a write up to hopefully help clear up some confusion about what is known.

  2. Thank you for the post, Lindsey. As a layperson (one not trained in nutrition or science), it is quite difficult to sort through the contradictory assertions made by the various "camps" in nutrition (e.g., paleo vs. vegan).

    One question for you: do you think that lectins pose any risk to persons with autoimmune diseases? As you are most likely aware, the paleo camp claims that autoimmune sufferers should avoid lectins (while others, e.g., Joel Fuhrman, suggest that autoimmune sufferers should adhere to a strict vegan diet that includes legumes).

    Thanks again!

  3. Some interesting and I believe good points. My brother and his girlfriend follow the Paleo lifestyle and believe that grains and legumes are bad because of their high carb count (Which should be somewhat of a concern, moderation in all things IMO). I will have to discuss Lectins with them at some point and see what they have to say.