NHD Issue 149 Lectin-free diet

DIET TRENDS

THE LECTIN-FREE DIET Lectins are a group of proteins that cause red blood cells to clump together by binding to carbohydrates.1 The lectin-free diet involves heavily restricting lectins such as gluten and certain lectin-containing foods. This article looks at the evidence for and risks involved in this restrictive diet.

Maeve Hanan UK Registered Dietitian Freelance

Maeve works as a Freelance Dietitian and also runs the blog Dietetically Speaking.com, which promotes evidence-based nutrition and fights nutritional nonsense.

REFERENCES Please visit: https://www. nhdmag.com/ references.html

The lectin-free 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 (ie, 16.8kg).2 The theory is that 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 (see Table 1). Dr Gundry advises the following: • 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.

EXAMINING THE EVIDENCE FOR THE LECTIN-FREE DIET

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, as mentioned earlier, but this evidence is not robust.4 For example, lectins can remain undigested in the human 8

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gastrointestinal tract.4 Human antibodies have also been found to form in response to consuming the type of lectins found in bananas 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), and actually indicates exposure rather than intolerance to specific foods.

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 nutrients.3,11 Fortunately, soaking and 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 wheatgerm (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 (ie, wheatgerm is cooked and then digested), consuming wholegrain wheat products 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. Any improvement that occurs whilst on this diet is likely to be related to other dietary factors. For instance, reduction of gut issues may be related to a reduced intake

DIET TRENDS Table 1: Foods containing lectins3-5 Beans, lentils, chickpeas and peas

Peanuts (and peanut-based products)

All grains, especially wheat, rice and corn and products made from these like bread and cake

Dairy products (Dr Gundry encourages A2 milk instead)

Most types of fruit, especially goji berries, cherries and blackberries (seasonal fruit is thought to be lower in lectins)

Meat from corn-fed cattle (Dr Gundry recommends grass-fed meat instead)

Most types of vegetables, especially butternut squash, pumpkin and ‘nightshade vegetables’ like: peppers, tomatoes, aubergine and potatoes

Oregano, parsley, peppermint nutmeg and spices

of FODMAPs, as many lectin-containing foods are also high in FODMAPs. Similarly, weight loss may be related to a reduction in calories, as the lectin-free diet is very restrictive. However, there are more targeted and established ways to achieve these benefits without using this diet.

Furthermore, as with all restrictive diets, there are health risks to consider related to this.

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 that should be diagnosed by a doctor. Therefore, there is no need for the general public 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 is needed when considering introducing certain allergenic foods to infants who have a high risk of food 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 A review from 2016 concluded that the lectins found in mushrooms may have anti-cancer properties and ‘these biomolecules [may have potential as] novel antitumor drugs in the 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 weight loss and metabolic health.23,24 These are also a good source of plant-based protein, fibre, B vitamins and a number of minerals. The lectinfree 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 to a reduced risk of heart disease, Type 2 diabetes, bowel cancer and allcause mortality.25,27 Beans, wholegrains and certain vegetables are also prebiotics that 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 These foods are also high in fibre and low in calories, so there is a chance that these may be replaced with higher calorie options.

Furthermore, as with all restrictive diets, this 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 dried 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 that contain lectins. In fact, these tend to be really nutritious plant-based foods, so cutting these out could lead to a number of health issues. 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. www.NHDmag.com November 2019 - Issue 149

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This material is for healthcare professionals only

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References: 1. Dupont C et al. Br J Nutr 2012; 107:325–338. 2. Lothe L et al. Pediatrics 1989; 83:262–266. 3. Baldassarre ME et al. J Pediatr 2010; 156:397–401.

4. Nermes M et al. Clin Exp Allergy 2011; 41:370–377. 5. Canani RB et al. J Pediatr 2013; 163:771–777. 6. Canani RB et al. J Allergy Clin Immunol 2017; 139:1906–1913.

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