Lectins: Good or Bad?

In today’s world, there is always some new type of diet trending, whether it’s paleo, Whole 30, keto, or whatever other crazy fad diets exist. Most of these diets involve eliminating foods or large food groups from your diet, which, in my opinion, is never a good idea. Why? Because when we eliminate certain foods, we miss out on a variety of nutrients found within those foods – nutrients that our bodies need to function properly and keep us healthy! Plus, eliminating foods causes many people to view that food as “bad” or “off-limits”, thus increasing the desire to eat that food and increasing the chances of developing disordered eating patterns.

Lately, I’ve been seeing many “lectin-free” or “lectin-avoidance” diets floating around or seeing things on the Internet about why people should avoid lectins. Any time I see something like this, I immediately roll my eyes and think, “is THIS the new diet trend that our society is falling for?” After all, once something hits the Internet, it’s bound to go viral. And once it does, more and more people will start to believe it, even if it’s not true! Given my career and passion for nutrition, whenever I see a nutrition claim floating around, I immediately investigate. So when I started hearing more and more about this “lectin-free” diet trend, I had to do my research and find out whether or not this was credible information being thrown out there.

Before I give you my thoughts and the bottom line on this diet, it’s important to start from the beginning and first describe what lectins are and where they can be found.

What are Lectins?

Often referred to as “anti-nutrients”, lectins are proteins that can be found in almost every single organism. Lectins play very important roles in humans, animals, and plants, but it’s important to note that they are not all created equally – some have more benefits than others. Unfortunately, people on the Internet today (who claim to be “nutrition experts”) only tell you about the harmful effects of lectins and fail to mention that lectins can actually be very beneficial in human bodies.

In animals (such as humans), lectins bind to carbohydrates, glycoproteins, and other cells in the body, allowing the cells to properly communicate with each other. Essentially, they are like glue that holds different cells together and allows them to communicate so that the cells can do their job within our bodies. For example, they help initiate an inflammatory response and trigger our immune systems to fight off any foreign bacteria or toxins that may have entered our bodies, protecting us from disease or any harmful bacteria. In plants, lectins serve as a defense mechanism against microorganisms, pests, insects, or anything else that may be harmful to them. In addition, they contain nitrogen that plants need in order to grow properly.

As you can see, lectins play very important roles in animals, humans, and plants. However, not all lectins are beneficial for everyone. While lectins are generally not harmful for most humans, they may cause problems for those who suffer from food allergies or autoimmune illnesses (such as celiac disease, rheumatoid arthritis, irritable bowel disease, or colon cancer).

So why do they cause an issue for some people? Believe it or not, humans cannot digest lectins. Rather, they travel through our gut (digestive system), bind to other cells on the gut wall, and then once in the body, the lectin triggers an immune response and releases certain antibodies to defend against the lectin. When this happens, the antibodies not only attack against the foreign lectin, but also the cell to which the lectin is attached – meaning that normal body tissue cells can be damaged as well. This is what is referred to as an autoimmune disease – when the body mistakenly starts attacking its own healthy cells. If this happens repeatedly, nutrients may not be properly absorbed in the small intestine, and it can also cause damage to the gut wall, leading to uncomfortable side effects such as stomach discomfort, gas, bloating, diarrhea, or even vomiting. But I have some good news for you! Most people do not experience the harmful effects of this, and it is rare that our own cells start attacking each other. Still not convinced? Well I have some more good news for you! There are actually ways to reduce amounts of lectins in the food we eat, which further reduces the risk of developing these adverse effects.

Which Foods Contain Lectins?

Lectins are found in almost all organisms, however they are only present in about one third of the foods that humans actually consume. Foods most commonly known for containing lectins include nightshade vegetables, grains, dairy, legumes, and some fruits. As I previously mentioned, lectins can cause sensitivity in some people, however it is important to note that there are several different ways to destroy lectins in the foods we eat, including cooking, sprouting, and fermenting. Therefore, lectins do NOT pose a significant problems for most humans.

From all of the studies I reviewed and articles I read, the foods most commonly known for lectins include the following:

• Red kidney beans (dried)
• Soybeans
• Wheat – especially wheat germ
• Peanuts
• Nightshade vegetables – tomatoes, eggplants, peppers,
• Potatoes

From what has been studied so far, those are the foods highest in lectins. But remember when I said that not lectins are created equally? Well it’s true! Just because a food contains lectins doesn’t automatically mean it is “bad” for us. Let’s take a look into this further, shall we?

Red Kidney Beans:

Red kidney beans (the dried beans) contain very high levels of a lectin called phytohaemagglutinin – levels of up to 20,000 – 70,000 hau. Not sure what that means? I’ll spare you the details and just say this: that’s a lot. Even ingesting just a few raw red kidney beans can have serious effects (diarrhea, nausea, vomiting) and even toxic side effects, which is something we want to avoid at all costs. However, just because they contain harmful lectins doesn’t mean you should avoid them! That’s right – red kidney beans are still perfectly safe to eat, as long as you cook them! Multiple studies have shown that boiling red kidney beans for at least 10 minutes at 212^oF or higher can reduce the levels of phytohaemagglutinin to levels of 200 – 400 hau, which is considered perfectly safe to eat.

The bottom line? Dried (uncooked) red kidney beans can be toxic if consumed raw. In addition, slow cooking dried red beans may not heat them enough to destroy the harmful toxins. Therefore, your best bet is to always soak them before cooking, and then when you do cook them, boil them at least 10 minutes at high heat. Or, you can even buy canned beans (which are already cooked). Do this, and you’ll be perfectly fine to consume red kidney beans without any harmful effects!

Wheat:

Next up, we have wheat. Raw wheat and wheat germ are known to be high in lectins, and it is believed that just 1 gram contains up to 300 mcg of lectin. But think about it – do you ever eat raw wheat? Chances are that you don’t. Most wheat products that humans consume have been cooked or heated – think pasta, flours in breads, etc. In fact, in cooked pasta, lectins are completely undetectable¹, meaning that the heat treatment destroyed them! So for all of you pasta or bread lovers, good news – you can continue to eat your wheat and grains! In addition, soaking grains or buying sprouted grain products further eliminates any lectins that may have survived the heating process. If you’ve never tried it before, try soaking your grains or oats before cooking them, or purchase a loaf of whole-wheat sprouted bread from the grocery store.

Peanuts:

Did you know that peanuts are not actually considered nuts, but rather they are classified as legumes? And given that legumes are known to be higher in lectins, it’s no surprise that this little guy made our list of foods high in lectins. Peanuts are high in the lectin Peanut Agglutinin (PNA), however, unlike most other lectins, PNA cannot be destroyed very easily.

Studies have shown that eating the occasional bag of peanuts will not cause any harm to humans due to the lectin content. However, it’s important to note that peanuts can also be very high in aflatoxins (a harmful type of mold produced by fungi). While most peanuts grown in the United States do not contain enough aflatoxins to be harmful, it’s still important to be wary. Always store peanuts in a cool, dry place, and do not eat them if they appear to be shriveled, discolored, or damaged by heat.

Tomatoes:

Tomatoes are considered to be part of the nightshade vegetable family (along with potatoes, peppers, eggplants, and others), and many people argue that the lectins found in tomatoes can be extremely harmful. Tomatoes do, in fact, contain lectins, but multiple studies have shown that there is not enough evidence (on humans) to decide whether or not tomatoes are harmful.

One thing that’s very important to note here is that some people do experience adverse effects after eating tomatoes or tomato-based products. However, that’s likely NOT due to the lectins. Rather, it’s likely due to something called pollen food allergy syndrome or oral allergy syndrome. Therefore, if you are someone who experiences adverse reactions or an itchy mouth after eating tomatoes, you may want to visit your doctor and get checked out for a pollen allergy.

Potatoes:

Last, but certainly not least, we have potatoes. Just like peanuts, the toxins found in potatoes are resistant to heat and are not easily destroyed by cooking at high temperatures. In fact, up to 40-50% of the lectins still remain even after cooking.

Just like with tomatoes, some people have reported having a reaction to potatoes, and studies done on animals have shown that this maybe due to the lectin content. However, not enough studies have been performed on humans to verify this. Plus, studies done on humans have shown that some types of potatoes can actually reduce inflammation, which is a good thing!

Overall? Potatoes do contain lectins, however they have shown to be more beneficial than harmful, so go ahead and continue to eat potatoes!

What is the Lectin-Free Diet?

Recently, a “lectin-free diet” trend has emerged, and it involves avoiding the following foods:

• All grains (including quinoa, rice, pasta, anything with gluten, etc.)
• Beans and legumes (including peanuts, soy, peas, chickpeas, etc.)
• Nuts and seeds
• Dairy and eggs
• Night-shade vegetables (including tomatoes, potatoes, eggplants, peppers, etc.)
• Fruits (including goji berries, melons, and any fruits not currently in season)

Take a minute and re-read that list. Is it just me, or is that a LOT of foods to eliminate? Basically, this diet is telling you to get rid of several MAJOR food groups and instead focus on eating only fruits, certain veggies, meat, seafood, and eggs. Now don’t get me wrong – there’s certainly nothing WRONG with consuming these foods, however, they shouldn’t be the only foods you are eating. Grains, legumes, nuts/seed, dairy, and all other “lectin-free” foods are all very rich in nutrients, and avoiding them allows you to miss out on all of those nutrients.

What are the Risks vs. Benefits of the Diet?

As a dietitian, I like to consider myself a detective; before making my mind up about something, I like to do as much research as I can on the topic and gather as much information as possible. But I don’t just look at any old information (eh-hem… Google) – I only look at evidence-based information. This means that I read through scientific journal articles, read up on all of the studies performed, and focus on gathering science-based information that has evidence to support it.

While I’m gathering my information, I remain completely neutral on the subject – neither for it nor against it. Only when I have all of my information will I sort through it and them come to a conclusion.

Just like any decision in life where you list out the pros and cons, gathering nutrition information involves learning all about the risks and the benefits. So with that being said, here is the information that supports both sides of the lectin-free diet.

 Case FOR a Lectin-Free Diet:

By eliminating all of those foods from your diet, there has to be SOME sort of benefit, right? Otherwise, what’s the point of this diet? One of the main claims made by supporters of this diet is that lectins cause inflammation in the body, so by avoiding them, people can reduce inflammation-based diseases such as rheumatoid arthritis, celiac disease, diabetes, cancer, or heart disease.

Digging into this more, I found that this is, in-fact, partially true: mannose-binding lectin (MBL) (the most intensively studied human lectin) can promote mitochondrial damage in renal tubular cells. In fact, when blood work was taken from patients suffering from autoimmune diseases (such as type 1 diabetes, rheumatic heart disease, and lupus), it was found that these patients had higher levels of MBL levels².

So what does this mean? In simplest terms, it means that MBL (a type of lectin found in some foods) can, in fact, trigger an inflammatory response and cause complications for people with autoimmune diseases. HOWEVER, it’s important to note that the general population (those without serious diseases or illnesses) was not studied – these results were from people who already had major diseases. As a matter of fact, the article point-blank stated that “These results suggest that human mannose-binding lectin (MBL) might have a pro-inflammatory role, but the role needs to be further investigated”.² Not enough studies have been performed on this topic, so it cannot be concluded (yet) that lectins can cause a harmful inflammatory response on humans.

Furthermore, it’s important to note that a lectin-free diet can be beneficial for those who already have autoimmune disease. Repeat: it is beneficial for those who ALREADY have the disease; NOT for the general population who does not suffer from these diseases. Diving into this further, a study was performed on 800 people with autoimmune diseases, and throughout the study, these people consumed a diet with NO grains, beans/legumes, soy, peanuts, nuts, nightshade veggies, melons, grain-fed meats, milk, or squash. The results showed that after 6 months of eating this diet, patients had lower levels of TNF-alpha, which is a marker that signals there is inflammation in the body. ²

So what does this mean? It means that for people who already have autoimmune diseases, eliminating lectins can be beneficial, as it helps reduce inflammation and serious side effects. However, for everyone else, there have been no studies that have shown eating a lectin-free diet is beneficial.

The Case AGAINST a Lectin-Free Diet:

As I mentioned above, one of the MAJOR drawbacks of this diet is that it eliminates several food groups, all of which contain beneficial nutrients that our bodies need. In addition, many of the “lectin-free” foods that must be avoided actually have important disease-fighting roles in our body. For instance:

• People who eat beans on a regular basis have lowered risks of heart disease, colorectal cancers, and other types of cancers.The soluble fiber can also lower blood pressure and LDL (bad) cholesterol.¹
• Tomatoes are very high in lycopene, which is an antioxidant that helps protect the skin and create healthy, glowing skin. Tomatoes also help the cardiovascular system and make it harder for LDL cholesterol to build up, leading to a decreased risk of heart attack or serious heart issues.¹
• Many of these foods (including potatoes and whole grains) have antioxidants such as chlorogenic acid or ferulic acid that can lead to a reduction in heart disease and gallstones.⁴
• Studies have shown that eating at least 3 servings of whole grains per day can reduce the risk of colorectal and other cancers by 17%⁴ and can significantly reduce the rates of cardiovascular diseases. Why is this? Whole grains are very rich in fiber, which helps to fill you up and keeps you from eating less. Therefore, people who eat more whole grains tend to eat less processed food or red meats, and have more consistent blood sugar levels throughout the day.

These are just a few of the many benefits that these foods can have on our health. In addition, foods containing lectins also contain complex carbohydrates, fiber, vitamins, and minerals that our bodies need in order to keep us healthy and feeling good. Therefore, eliminating foods with lectins deprives your body of essential nutrients that it absolutely needs!

It’s also extremely important to note that the majority of studies done on lectins have been done with isolated lectins, not actual foods. This means that most of the studies have been done in labs using test tubes or animals – not on humans. Therefore, how do people link lectin-containing foods to certain health issues when clinical trials in humans have not even been conducted yet?! It just doesn’t make sense, and this just goes to show that you should never listen to online “health experts” unless they provide scientific evidence that backs up what they are saying!

Lastly, this diet involves the elimination of several major food groups, which can increase the chance of developing disordered eating patterns, or even full-blown eating disorders. In fact, according to The National Eating Disorders Association, “35% of “normal dieters” progress to pathological dieting and 20-25% of those individuals develop eating disorders”.⁶ Therefore, instead of dieting, most doctors or dietitians (including myself) will often times tell people not to diet, but rather to focus on making long-term lifestyle changes… NOT quick-fixes that diets claim to do.

My Opinion:

Now that I’ve gathered all of the information, it’s time for me to point out a few things I noticed.

As I was reading up on articles, I learned that foods containing lectins CAN trigger an inflammatory response in the body (I’ll spare you the scientific details). And constant inflammation in the body can certainly lead to the diseases listed above.  However, think of it like this: if we all eat lectins (or most people, at least), why doesn’t everybody have diabetes, arthritis, or other inflammatory disease? One reason for this is because our bodies are designed to protect us from harmful substances. Therefore, we have things like saliva, stomach acid, beneficial bacteria, and a mucosal lining in the intestine, to protect us from harmful lectins. Most people have natural defenses against harmful lectins, but there are some cases (people with systemic inflammatory diseases) when these natural defenses do not work, which is what leads to uncomfortable side effects after consuming lectins.

Plus, it’s also important to note that everybody reacts to foods different. Some people may not be able to tolerate dairy, but that certainly doesn’t mean they have to completely eliminate ALL lectins from their diet. The best advice I have for you is to find what works for you. If dairy doesn’t sit well with you, don’t eat it! If grains keep you full and give you energy to get through the morning, then by all means… eat them! Don’t avoid certain foods or follow certain diets just because someone tells you it’s the newest trend. Only you know what works best for your body, and it’s up to you to feed it what makes you feel good.

Furthermore, I found it really interesting that all of the research articles I found involved testing on rats. Not humans, but RATS. Now the last time I checked, humans and rats were certainly different, so how is it fair to conclude that what happens in rats will happen in humans? It’s not! Therefore, until more research is done on actual humans, it’s hard for me to determine whether or not lectins can be harmful toward humans.

Lastly (this is my final opinion, I promise), to me, the “lectin-free” diet just sounds like another fad diet that’s going to take off and gain popularity, just as Whole30, Paleo, or Vegan diets have recently done. All the non-scientific articles I found on the lectin-free diet claim that it’s the “miraculous cure-all” for diseases like arthritis, cancer, or diabetes. Or even weight loss. And as soon as I read that, a big red flag went off in my mind. Any diet that claims to make you “lose weight fast” or promises to cure serious diseases without providing any scientific evidence is a fraud. Run away!

The Bottom Line:

If you’ve made it to the end of this long article, congrats. I hope you’ve come to the conclusion that I do not support the lectin-free diet. Just to re-cap:

• Only about 30% of the foods we eat actually contain lectins. Of that 30%, most of the lectins can be destroyed or significantly lowered by cooking or heating the foods, making them safe and free from any adverse side effects.
• Nightshade veggies have shown to be an issue for some people, but that is unrelated to the lectin content and more related to pollen allergies or other allergies related to chemicals sprayed on the veggies/fruits.
• Foods containing lectins contain essential vitamins, minerals, and antioxidants that the human body needs to stay healthy and function properly.

All-in-all, the scientific evidence does not support the view that lectins are harmful to our health. Rather, what’s harmful to our health is promoting this idea which has led to many people being afraid to eat these healthy foods like beans and tomatoes.

Therefore, here’s my advice to you: ALWAYS do your research. If you do happen to start a diet, ask yourself why you’re doing it. Is it to lose weight? Is it to cure your arthritis or diabetes? If so, a diet probably isn’t the best choice for you. Rather, the best advice I have for you is to focus on making small changes every day to your lifestyle: eating more fruits, veggies, and protein, staying active in a way that makes you feel good, and sleeping more. After all, those are the keys to staying healthy and feeling great.

Sources:

1. Gong T, Wang X, Yang Y et al. Plant Lectins Activate the NLRP3 Inflammasome To Promote Inflammatory Disorders. The Journal of Immunology. 2017;198(5):2082-2092. doi:10.4049/jimmunol.1600145.
2. Koneti A, Linke M, Brummer E, Stevens D. Evasion of Innate Immune Responses: Evidence for Mannose Binding Lectin Inhibition of Tumor Necrosis Factor Alpha Production by Macrophages in Response to Blastomyces dermatitidis. Infect Immun. 2007;76(3):994-1002. doi:10.1128/iai.01185-07.
3. Matucci A, Veneri G, Dalla Pellegrina C et al. Temperature-dependent decay of wheat germ agglutinin activity and its implications for food processing and analysis. Food Control. 2004;15(5):391-395. doi:10.1016/s0956-7135(03)00104-x.
4. Costabile A, Klinder A, Fava F et al. Whole-grain wheat breakfast cereal has a prebiotic effect on the human gut microbiota: a double-blind, placebo-controlled, crossover study. British Journal of Nutrition. 2007;99(01). doi:10.1017/s0007114507793923.
5. Eating Disorders and Dieting – Weight Management. Eating Disorder Hope. 2018. Available at: https://www.eatingdisorderhope.com/treatment-for-eating-disorders/special-issues/dieting. Accessed May 8, 2018.