The Lectin-Free Diet

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This article was first published in the November 2019 edition of NHD magazine.


What is the Lectin-free Diet? 

This diet involves heavily restricting lectins in the diet, which are a group of proteins that cause red blood cells to clump together by binding to carbohydrates.1 For example, gluten is a type of lectin. 

This diet has been promoted by an American Cardiologist called Dr Steven Gundry (author of: ‘The Plant Paradox’), and has been further popularised by celebrities such as Gwyneth Paltrow and Kelly Clarkson. In fact last year Kelly Clarkson hit the headlines with the dramatic claim that due to the lectin-free diet she no longer needs medication for an autoimmune condition, and that it helped her to lose 37 pounds (i.e. 16.8kg).2 

The theory is lectins are present in plants in order to defend them against insects and animals, and that these lectins can harm humans by binding to the lining of our gut. Dr Gundry has claimed that this leads to inflammation and health issues, such as autoimmune disorders, diabetes, leaky gut syndrome, heart disease and neurodegenerative diseases.3 

Lectins are found in a variety of foods including:3-5

  • Beans, lentils, chickpeas and peas. 
  • All grains – especially wheat, rice and corn and products made from these like bread and cake.
  • Most types of fruit – especially goji berries, cherries and blackberries (seasonal fruit is thought to be lower in lectins).
  • Most types of vegetables – especially butternut squash, pumpkin and ‘nightshade vegetables’ like: peppers, tomatoes, aubergine, and potatoes.
  • Peanuts (and peanut-based products). 
  • Dairy products (Dr Gundry encourages A2 milk instead).
  • Meat from corn-fed cattle (Dr Gundry recommends grass-fed meat instead)
  • Oregano, parsley, peppermint nutmeg and spices

Dr Gundry also advises: 

  • Peeling and deseeding fruit and vegetables to reduce the lectin content. 
  • Buying fruit in season so these are eaten “at the peak of ripeness”.
  • Choosing refined starchy carbohydrates over wholegrain versions.

What Does the Evidence-Base Say?

There is some evidence from animal studies that lectins may bind to the intestinal wall and interact with digestion and the immune system.4,6 It is thought that this may also occur in humans to some degree, but this evidence is not robust.4 

Human antibodies have also been found to form in response to consuming the type of lectins found in banana and legumes.5, 7-8 However, the type of immune response found in these studies is not used as a reliable marker of food intolerance (IgG antibodies). 

Certain types of beans, especially raw red kidney beans, contain lectins which can be toxic to humans (such as ricin and phytohaemagglutinin). Consuming this type of lectin can lead to vomiting and diarrhoea.9-10 Lectins can also act as ‘anti-nutrients’ by blocking the digestion and absorption of vitamins, minerals and other nutrients3, 11.

Fortunately, soaking then boiling beans before eating them significantly reduces the level of lectins present and weakens their binding ability, rendering them safe to consume.11-12

The process of canning beans has also been seen to reduce the lectin content further.13 

In-vitro studies have found that mixing wheat-germ (containing lectins) with human blood cells can cause inflammation.2 But when human studies have been carried out in a way which is more similar to real-life (i.e. wheat germ is cooked and then digested), consuming wholegrains is seen to actually reduce inflammation.2,14-15 

Despite dramatic claims about the lectin-free diet, there is no direct evidence that this boosts weight loss or reduces disease risk in humans.

If improvements do occur on this diet, it is likely to be related to other dietary factors. For instance, reduction of gut issues may be related to a reduced intake of FODMAPs, as many lectin-containing food are also high in  FODMAPs. Similarly, weight loss is due to a reduction in calories, and the lectin-free diet is very restrictive. However, there are safer and more established ways to achieve these outcomes without using this diet.

Some people may be allergic to lectins, such as the proteins found in certain types of beans and nuts.9 But this is a medical condition which should be diagnosed by a doctor.

Therefore, the general public does not need to avoid lectins for this reason. In fact avoiding possible allergenic food may increase the risk of food allergy, especially in early life (although medical support may be needed when considering introducing allergenic food for infants at high risk of allergy).16-17 

There is also evidence related to possible health benefits of lectins. For example, the fact that lectins can survive digestion may be beneficial for the gut, and gut-mediated metabolic and immune responses.18

Similarly, a review from 2016 concluded that the lectins found in mushrooms may have anticancer properties and “these biomolecules [may have potential as] novel antitumor drugs in near future”.19

Risks Related to the Lectin-free Diet

This diet limits a number of foods which are known to be really good for us.

Firstly, there is very good evidence that consuming plenty of fruit and vegetables (especially vegetables) is associated with a reduced risk of heart disease, cancer and all-cause mortality.20

However, the lectin-free diet specifically limits a number of fruit and vegetables which are known to be beneficial. Such as the possible anti-cancer activity of mushroom lectins as discussed above. Tomatoes and blackberries have also been seen to reduce inflammation and the risk of chronic diseases.21-22

Similarly, consuming cooked beans and pulses can help to reduce inflammation, and improve metabolic health.23-24 These are also a good source of plant-based protein, fibre, B-vitamins and a number of minerals. 

The lectin-free diet also limits wholegrains, although these are highly nutritious and a great source of fibre. There is good evidence that a high intake of wholegrains is linked with a reduced risk of heart disease, type two diabetes, bowel cancer, and all-cause mortality.25-27  

Beans, whole-grains and certain vegetables are also prebiotics which feed our healthy gut bacteria and contribute to better gut health.28 Moreover, research is emerging that good gut health plays an important role in overall health by reducing the risk of chronic disease, and improving metabolism and immunity.27

As with all restrictive diets, the lectin-free diet runs the risk of creating an unhealthy relationship with food, or triggering disordered eating.

Conclusion

From a food safety point of view, we should soak then cook dry beans well before eating, as they can contain a type of lectin which is toxic to humans.

But beyond this, there is no good evidence that we should be reducing our intake of all foods which contain lectins.

In fact, these tend to be really nutritious plant-based foods, so cutting these out could increase the risk of chronic health conditions.

Overall, there is much more evidence that foods deemed to be high in lectins are good for us, as compared with sparse evidence that these may cause harm. 

References

  1. Pubmed (2003) ‘Lectins’ [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/mesh/68037102]
  2. LiveScience website (2018) “No, You Probably Shouldn’t Follow Kelly Clarkson’s ‘Lectin-Free’ Diet” [accessed January 2019 via: https://www.livescience.com/62914-what-are-lectins-plant-paradox.html]
  3. “The Plant Paradox: The Hidden Dangers in “Healthy” Foods That Cause Disease and Weight Gain” by Stephen Gundry (2017).
  4. Van Buul & Brouns (2014) “Health effects of wheat lectins: A review” [accessed January 2019 via: https://www.sciencedirect.com/science/article/pii/S0733521014000228  
  5. Vasconcelos & Oliveira (2004) “Antinutritional properties of plant lectins” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/15302522]
  6. Vojdani (2015) “Lectins, agglutinins, and their roles in autoimmune reactivities” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/25599185]
  7. Koshte et al. (1990) “Isolation and characterization of BanLec-I, a mannoside binding lectin from Musa paradisiac (banana)” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/2268297
  8. Koshte et al. (1992) “The Potent IgG4-inducing antigen in banana is a mannose binding lectin, BanLec-I” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/1582693
  9. Kumar et al. (2013) “Clinical complications of kidney bean (Phaseolus vulgaris L.) consumption” [accessed January 2019 via: https://www.sciencedirect.com/science/article/pii/S0899900712004339
  10. Freed (1999) “Do dietary lectins cause disease?” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1115436/
  11. Fabbri & Crosby (2016) “A review of the impact of preparation and cooking on the nutritional quality of vegetables and legumes” [accessed January 2019 via: https://www.sciencedirect.com/science/article/pii/S1878450X15000207#bib20
  12. Venter & Thiel (1995) “Red kidney beans–to eat or not to eat?” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/7777998
  13. Pedrosa et al. (2015) “Effects of industrial canning on the proximate composition, bioactive compounds contents and nutritional profile of two Spanish common dry beans (Phaseolus vulgaris L.)” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/25053030]
  14. Xu et al. (2018) “Whole grain diet reduces systemic inflammation: A meta-analysis of 9 randomized trials.” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/30412134]
  15. Vitaglione et al. (2015) “Whole-grain wheat consumption reduces inflammation in a randomized controlled trial on overweight and obese subjects with unhealthy dietary and lifestyle behaviors: role of polyphenols bound to cereal dietary fiber.” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/25646321]
  16. Du Toit et al. (2015) “Randomized Trial of Peanut Consumption in Infants at Risk for Peanut Allergy” [accessed January 2019 via: https://www.nejm.org/doi/full/10.1056/NEJMoa1414850]
  17. Perkin et al. (2016) “Randomized Trial of Introduction of Allergenic Foods in Breast-Fed Infants” [accessed January 2019 via: https://www.nejm.org/doi/full/10.1056/NEJMoa1514210]
  18. Pusztai A. Dietary lectins are metabolic signals for the gut and modulate immune and hormone functions. Eur J Clin Nutr. 1993;47(10):691-699
  19. Singh RS, Kaur HP, Kanwar JR. Mushroom lectins as promising anticancer substances. Curr Protein Pept Sci. 2016;17(8):797-807 
  20. Aune et al. (2017) “Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality – a systematic review and dose-response meta-analysis of prospective studies “ [accessed January 2019 via: https://academic.oup.com/ije/article/46/3/1029/3039477#.WK8GCT_AOQE]
  21. Cheng et al. (2017) “Tomato and lycopene supplementation and cardiovascular risk factors: A systematic review and meta-analysis” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/28129549]
  22. Dai et al. (2017) “Characterization of blackberry extract and its antiproliferative and anti-inflammatory properties” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/17651061]
  23. Hermsdorff et al. (2011) “A legume-based hypocaloric diet reduces proinflammatory status and improves metabolic features in overweight/obese subjects” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/20499072]
  24. Mollard et al. (2012) “Regular consumption of pulses for 8 weeks reduces metabolic syndrome risk factors in overweight and obese adults” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/22916807]
  25. Reynolds et al. (2019) “Carbohydrate quality and human health: a series of systematic reviews and meta-analyses” [accessed January 2019 via: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(18)31809-9/fulltext]
  26. Aune et al. (2016) “Whole grain consumption and risk of cardiovascular disease, cancer, and all cause and cause specific mortality: systematic review and dose-response meta-analysis of prospective studies” [accessed January 2019 via: https://www.bmj.com/content/353/bmj.I2716.full]
  27. Schwingshackl et al. (2017) “Food groups and risk of type 2 diabetes mellitus: a systematic review and meta-analysis of prospective studies” [accessed January 2019 via: https://link.springer.com/article/10.1007/s10654-017-0246-y]
  28. Florowska et al (2016) “Prebiotics as functional food ingredients preventing diet-related diseases” [accessed January 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/26961814]

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