I recently saw part of an ad in which Dr. Steven Gundry holds up a tomato and proclaims that tomatoes are one of the worst foods that you could possibly eat. I don’t know if my grandparents and parents would agree seeing that they raised hundreds of tomatoes every year and canned or made salsa with them. In fact, I grew up eating lots of tomatoes in the winter in sauces, chilis, etc. Were my parents and grandparents wrong? Were they actually harming all of us and not even knowing it? And why is this important for you, as far as health and running performance?
What could be the issue? After all, tomatoes are an excellent source of biotin, potassium, iron, and zinc. For running performance these nutrients are important for skeletal muscle and nerve function, energy production from carbohydrates and fats, muscle repair and growth, and prevention of muscle cramping. Tomatoes are also one of the best sources of lycopene, an antioxidant that reduces inflammation, as well as conditions related to oxidative stress. Meta-analyses have suggested that tomatoes may be protective against cancer, especially that of the prostate. This likely has something to do with their lycopene content, which has been shown to slow the progression of cancer and tumor cells. Tomatoes also appear to benefit heart health, by lowering both your LDL (“bad”) cholesterol and blood pressure among other cardioprotective effects (Xu et al 2016, Rowles et al 2018).
However, tomatoes also contain another substance that begins with “L” that can be harmful, which is lectins. This is why Dr. Gundry was proclaiming that we should not eat tomatoes. Is he right?
Lectins are a class of antinutrients. In my last post, I briefly discussed antinutrients and went more in depth on one class of antinutrients, oxalates. In this post, I will discuss lectins, including: the foods in which lectins are highly concentrated, the impact of lectins on health and running performance, how we can reduce lectin content in foods, and whether or not we should be eating foods like tomatoes.
What Are Lectins?
Lectins are proteins present in many plants and concentrated in legumes, whole grains, and certain fruits and vegetables. The lectins in food bind to carbohydrates, forming glycoproteins. These glycoproteins perform many functions within the body, from regulating the immune system to keeping protein levels in the blood under control. Since lectins are antinutrients, they can’t be digested in the body and pass through the digestive system intact. Lectins help a plant defend itself against microorganisms, pests, and insects, and help the plant be able to propagate itself, even if eaten.
Lectins have multiple health benefits, as mentioned, however, they can also have adverse health effects. So, it is helpful to be aware of foods high in lectins.
What Foods Are High in Lectins?
The ten foods with the highest concentration of lectins are:
- Potatoes (excluding sweet potatoes)
- Wheat germ
- Red kidney beans
What Are The Adverse Effects Associated with Consumption of Lectins?
Lectins can have several adverse effects on the body. The severity of these effects will vary depending on the level of consumption of lectins and an individual’s sensitivity to lectins. The most significant impact lectins can have are that they can damage the intestinal lining of the gut, which can lead to symptoms of irritable bowel syndrome (abdominal pain/distention, diarrhea/constipation, flatulence, nausea, weight loss) and increase the permeability of the intestine, which can allow undigested food particles into the blood to circulate the body. This is referred to as “leaky gut” and can lead to significant health issues, especially autoimmunity. This is significant because autoimmunity involves the body’s immune system mounting a response against not only foreign invaders, such as undigested food particles, but the body’s own tissue. Lectins themselves are undigested and can enter the bloodstream triggering an immune response. For lectins this immune response has been shown to affect the joints potentially leading to rheumatoid arthritis (RA). In addition, lectins can facilitate the preferential growth of specific bacteria which can make an individual more susceptible to RA (Wang et al. 1998, Cordain et al. 2000).
Lectins can also facilitate bacterial overgrowth and contribute to leptin resistance, a condition that causes the brain of an overweight person not to receive the signal that the stomach is full (Jönsson et al. 2005). Lectins can disrupt small-intestine metabolism (the chemical processes that occur within a living organism in order to maintain life) and damage the gut villi (finger-like projections on the small intestine’s lining that absorb nutrients). Lectins also act as an antinutrient, meaning that they can interfere with digestion and absorption of foods, upping the risk of nutritional deficiencies. This is especially significant for runners, who need to constantly replenish nutrients throughout their training.
Certain people are more sensitive to specific types of lectins than others. If you eat something that contains the types of lectins you’re sensitive to (or a lot of lectins that you’re less sensitive to), the result is inflammation that you may experience as brain fog, sore joints, bad skin, or even migraines. For example, the type of lectins found in the nightshade family of plants, which includes tomatoes, eggplants, peppers, and potatoes, is one that many people are sensitive to. It is a common autoimmune trigger that has been linked to a significant percentage of RA cases and is a trigger for skin problems.
What Can You Do To Minimize Lectins?
Some research seems to indicate that taking in large quantities of raw lectins could have negative health effects. Although this may be true, especially when consumed in excess or for those individuals with lectin sensitivities, cooking, sprouting, soaking and fermenting your foods can cut down on lectin concentration to help promote better health. Soaking grains and legumes prior to consumption can reduce lectin content and enhance their nutritional value and reduce other antinutrient content. Cooking legumes, in particular, can nearly eliminate all lectins, with one study out of the Roweti Research Institute’s Division of Nutritional Sciences in Scotland even showing that boiling soybeans for as little as five minutes virtually eliminated lectin activity (Pusztai et al 1998). Because legumes are generally eaten cooked and not raw, this means that most legumes in your diet are likely very low in lectins.
Soaking and sprouting grains and seeds can also be an effective method to reduce lectin content (Koval’chuk 2006). Sprouting, also known as germination, is a process that involves soaking seeds for up to 24 hours and then repeatedly rinsing and draining them every few hours for several days at a time. Not only can sprouting decrease the lectin content of your grains and legumes, but it can also enhance the nutritional profile of your foods while reducing the amount of other antinutrients that interfere with digestion (Chingakham et al 2015, Luo et al 2012).
Fermenting your foods can also help reduce the amount of lectin content. Fermentation allows the beneficial bacteria to digest the lectins and other antinutrients in foods to enhance the overall nutritional profile (Oluwole et al 2013). Plus, fermentation supplies valuable probiotics to your diet to improve gut health.
Back to our friend the tomato, cooking vegetables, especially pressure cooking, can reduce the lectin content. Also, cooking or stewing tomatoes and eating them with healthy fat can enhance the absorption of lycopene. This is seen in traditional cultures with Italian dishes pairing olives with stewed tomatoes, or Mexican cuisine that combines avocados and various tomato-based sauces and spreads.
In addition, if you are eating raw tomatoes you may want to opt for varieties like Roma, which have a lower lectin content.
How Are Lectins Beneficial?
To complicate matters…
Lectins also play many vital roles within the body. Lectins are involved in immune system regulation, and some research indicates that they may have antimicrobial properties. In fact, they have been shown to be effective against several types of bacteria, including the strain that causes staph infections and E. coli. Lectins may also help fight off fungi and viral infections (Lagarda-Diaz et al 2017). In addition, a review study found that certain lectins may possess anticancer properties. Specifically, these plant lectins can modify the expression of specific immune cells and alter signaling pathways to help kill off cancer cells and block tumor growth (Jiang et al 2015).
Therefore, the results of these studies suggest that having some lectins in the diet can be of benefit. However…
Who Should Avoid Nightshades and/or Other High-Lectin Containing Foods
Those individuals with a food allergy or sensitivity to specific nightshades should limit or avoid consuming them. There are anecdotal reports from people claiming that when they no longer eat nightshades, they stop experiencing painful inflammatory symptoms. It is possible that some of these people have an allergy of some kind. Therefore, it can be beneficial to keep a food log or journal and record how certain foods may affect you, such as causing sore joints, skin problems, or migraines.
There have been rare cases in which people have an acute allergic reaction to a nightshade, like an allergy to tomatoes. If that’s the case for you, then, by all means, don’t consume tomatoes!
People with inflammatory bowel diseases like Crohn’s disease or ulcerative colitis may also find that they do better when they avoid nightshades. Some of these conditions can cause intestinal permeability, and a number of test tube and animal studies have suggested that intestinal permeability can be negatively impacted by excessive intake of the alkaloids (concentrated in areas that are green) in potatoes (Patel et al 2002), fiber in tomatoes (Carreno-Gómez et al 1999), and capsaicin in peppers (Jensen-Jarolim et al 1998).
Lectins are present in many of the plant foods that we eat, however they are highly concentrated in certain foods such as grains, legumes, and nightshades. Lectins can have beneficial, as well as adverse, effects on health and performance. Lectins have been shown to have some beneficial effects as far as immune system regulation and they can have antibacterial, antiviral, antifungal, and anticancer properties. Also, the foods that are highly concentrated in lectins contain many beneficial nutrients for health and performance. For example, tomatoes contain zinc, potassium, iron, and biotin which are important for skeletal muscle and nerve function, energy production from carbohydrates and fats, muscle repair and growth, and prevention of muscle cramping, fatigue, and inflammation.
On the other hand, lectins are antinutrients that can have certain adverse health effects including damaging the intestinal lining of the gut, stimulating the development of rheumatoid arthritis, and affecting nutrient absorption. The severity of these effects will vary depending on the level of consumption of lectins and an individual’s sensitivity to lectins. Therefore, it is important to note or keep a food log or journal and record how certain foods, such as nightshades, are affecting you. Cooking, sprouting, soaking and fermenting your foods can reduce lectin concentration to help promote better health.
Individuals with inflammatory bowel diseases like Crohn’s disease or ulcerative colitis, as well as those with lectin sensitivities may find that they do better when they avoid foods with high lectin concentration, especially nightshades.
However, unless you have inflammatory bowel disease or sensitivities to lectins, rather than focusing on eliminating lectin-rich foods from the diet altogether, such as tomatoes, it’s better to work on reducing lectin content through cooking, soaking, sprouting or fermenting foods instead, so you can still take advantage of the health-promoting properties of these nutritious foods.
Please let me know if you have any questions, or if I can be of help in any way. I would love to hear from you.
Your friend and coach,
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Dr. Steven Gundry. The Plant Paradox: The Hidden Dangers in ‘Healthy’ Foods that Cause Disease and Weight Gain.
Dave Asprey. The Bulletproof Diet.
Yuri Elkaim. Super Nutrition Academy, Module 6 Lesson 4.
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