This is the second of a two-part post that first appeared on GreenMedInfo.com. Information about the author follows the references. If you missed the first post, read it at http://aswellasicanbe.com/chronic-illness/fight-autoimmune-diseases/
A Low Lectin Diet As a Therapeutic Intervention for Autoimmune Disease
In effect, researchers propose that minimizing intake of lectin-rich food substrates can lessen the persistent antigenic stimulation that results in defective immunological tolerance and causes the immune system to target the body itself (Source). Immunological tolerance is essentially the ability of the immune system to discriminate self from non-self, which is lost with autoimmune disorders (Source). This is also the rationale behind therapeutic regimens such as the paleo diet and autoimmune paleo protocol.
Whereas acute lectin toxicity in humans is insidious, manifesting with symptoms such as nausea, abdominal distention, vomiting, and diarrhea, “In experimental animals fed on diets containing plant lectins the evident symptoms are a loss of appetite, decreased body weight and eventually death” (Source). Therefore, a disease resulting from the effects of lectins can be long-latency, incubating in a sense for many years or decades before culminating in a life-threatening disorder. Thus, it is difficult to correlate symptoms with lectins, and many people may not make a connection between their health issues and the foods they are eating.
A Healthy Dose of Skepticism: More Research is Required
A well-warranted criticism of lectin science and the paleo community is that the foundations of their anti-nutrient arguments are based on animal and in vitro (cell culture) studies, which may not be fairly extrapolated to human physiology. On a ladder representing evidentiary quality, where meta-analyses and systemic reviews are positioned at the top, these study designs occupy lower rungs, are oftentimes found to be methodologically inadequate, and may not predict human reactions (Source).
Many of the studies upon which paleo advocates hang their hats are rodent models, where laboratory animals are fed disproportionately large levels of lectins or lectins from raw legumes, which may not be applicable to human health (Source). The lectin soybean agglutinin (SBA) is commonly cited as inducing intestinal permeability in paleo circles, yet piglet models have shown that disturbed barrier function only occurs when SBA is included at high levels in their diets (Source). Thus, a dose-response relationship may occur and a threshold may be reached beyond which lectin consumption is not tolerated. In addition, some of these same animal models, in fact, reveal that lectin toxicity is reduced by inclusion of oligosaccharides and simple sugars such as sucrose, which naturally occurs in the diet, given the specificity of lectins for carbohydrate moieties (Source).
Also commonly demonized is the peanut lectin, which has been shown in cell culture studies to disrupt the cytoskeletal (filaments and tubules) organization of intestinal tight junctions and lead to intestinal permeability, a phenomenon which may account for the increased allergenicity of peanuts. Paleo champions recommend avoidance of peanuts due to their atherogenic effects in animal models, yet human trials demonstrate that peanuts may improve cardiovascular risk, illustrating that animal studies may not be generalizable to human physiology (Source).
Another point with merit is that many foods included on the paleo diet, such as avocado, banana, beetroot, blackberries, broccoli, Brussels sprouts, cabbage, cantaloupe, carrots, cauliflower, cherries, cucumber, garlic, grapes, leek, mushrooms, mustard, oregano, parsley, peach, pomegranate, potato, pumpkin, taro, tea, tomato as well as various spices and nuts have all been demonstrated to exhibit lectin activity (Source)(Source). This underscores the need to distinguish between lectins and potentially toxic lectins, as the latter may predict poor physiological responses, with the immunostimulatory and gut barrier compromising effects of prolamins and agglutinins being implicated as some of the worst.
Moreover, lectin content varies, and some lectins are relatively innocuous since they are denatured by cooking (Source). Other studies, however, suggest that some lectins are not neutralized with cooking, so researchers have not yet arrived at firm conclusions in this respect. Historically, many ancestral practices, such as soaking and sprouting grains, treating corn with lye, eliminating the hull and bran of brown rice to consume the lower lectin white rice, or peeling and de-seeding vegetables, became intuitive cultural rituals in order to minimize lectin consumption. However, most of us in the industrial age have abandoned these practices and adopt mono-diets where so-called anti-nutrient rich foods are ingested in excess. Soaking, sprouting, and cooking nuts and beans, as well as fermenting vegetables, have been similarly elucidated to decrease the content of phytates, another much-maligned anti-nutrient (Source).
However, whether these approaches have scientific merit is still hotly contested. A recent randomized, cross-over trial challenges the validity of these preparation techniques and concluded not only that soaking did not improve gastrointestinal tolerance, but flatulence ratings were higher for all points for soaked nuts compared to unsoaked. Moreover, the researchers state, “Recommendations to soak nuts prior to consumption to reduce phytate concentrations and improve gastrointestinal tolerance have received much attention in the popular press. This is despite no supporting scientific evidence for the practice” (Source).
Bioindividuality May Dictate Vulnerability to Anti-Nutrients
One reason lectins may pose a problem for some individuals but not others is due to genetic variability in the cell surface glycoconjugates (carbohydrates covalently linked with other chemical species) to which lectins attach, and due to the fact that the glycoprotein tips to which lectins bind are hidden behind sialic acid molecules (Source). However, this protective screen of sialic acid molecules can be removed by the enzyme neuraminidase that accompanies pathogens such as influenza and streptococci, which cause the flu virus and Strep throat, respectively (Source). In fact, this explains the ability of infections to induce or exacerbate autoimmune disease: “This facilitation of lectins by micro-organisms throws a new light on postinfectious diseases and makes the folklore cure of fasting during a fever seem sensible” (Source).
The prevailing gut ecology may also influence susceptibility to the adverse effects of lectins. For instance, the red kidney bean lectin PHA is lethal for rats when administered in high doses, but non-toxic in germ-free animals devoid of a microbiome (Source). These findings suggest that the toxic effects of PHA could be mediated by its ability to enhance navigation of gut bacteria into systemic circulation (Source).
The centrality of the microbiota to food reactions is also applicable to another anti-nutrient frequently cited in the paleo community, phytic acid. Also known as phytate, the storage form of phosphorus in plants analogous to phosphorus in animals, phytic acid is often cited as another reason why grains and beans are excluded from a paleo diet. Phytates have been observed to bind to and inhibit absorption of minerals such as calcium, zinc, and magnesium (Source). However, phytates have also been demonstrated to elicit paradoxical hormetic effects, having antioxidant, anticancer, anti-inflammatory, and anti-osteoporotic activity (Source).
Also neglected is the fact that the commensal microbes that inhabit the gut synthesize phytase, an enzyme that degrades phytate, in a dose-dependent manner (Source). In someone with dysbiosis, however, a condition applicable to almost anyone with chronic illness, this ability may be compromised. Much of the reaction to anti-nutrients may, therefore, be contingent upon the functional medicine pillar of biochemical individuality, which is a confluence of genetic proclivities, microbial terrain, environmental stressors, and the prevailing landscape of the body.
When to Implement a Low-Lectin Diet
While some lectins such as WGA and gluten are unequivocally inflammatory in most cases of chronic illness, the science on lectins is far from settled. For example, lectins may exhibit beneficial hormetic effects, as some studies reveal that lectins induce apoptosis and autophagy (self-devouring) of cancer cells, modulate endocrine and immune function, and serve as metabolic signals for the gut.
However, because of the detriment to quality of life incurred by autoimmune disorders, a therapeutic trial of a low-lectin dietary regimen like the paleo or autoimmune paleo diet is deserving of consideration. While there is a paucity of high-quality peer-reviewed human studies, the clinical experience of countless physicians supports the efficacy of these interventions. In addition, data is accruing in favor of these dietary interventions for cardiometabolic conditions and autoimmune diseases, which is further described in my article “Landmark Study Suggests Efficacy of Autoimmune Paleo Protocol”.
The success of these dietary protocols may not only be attributed to their eschewal of immunogenic foods, but also to their inclusion of bioavailable nutrients. According to the hierarchy of healing practiced by naturopathic doctors, less invasive, low-risk modalities should be attempted first when possible according to the therapeutic order, a philosophy with which dietary strategies such as these are compatible.
Researchers echo the aforementioned sentiments, with: “Although it is common knowledge that some dietary lectins can adversely affect the growth and health of young animals…it has not been rigorously established that findings with animals are also directly applicable to humans. However, because the glycosylation state of the human gut is basically similar to that of higher animals, it may be confidently predicted that the effects of dietary lectins will have similarities in both humans and animals” (Source). Self-experimentation through an elimination diet is the gold standard for identifying reactions to food constituents, and lectins are no exception.
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