Cooking legumes in high temperatures

Legumes should be boiled in high temperatures

Pawel Malczewski
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Short summary

Cooking legumes, especially beans, requires high temperatures to reduce a toxin called phytohaemagglutin.

Cooking beans in slow cookers or sous-vide baths may not be enough and may even increase the toxicity levels to 5 times or more than raw beans depending on the temperature. For a quick answer click here.

Explanation

Lectins are a form of protein that bind to carbohydrates and are present in most plants and about 30% of the food we eat. The lectins protect plants from being eaten by pests and insects and against pathogens such as fungus. (1)Vojdani A. Lectins, agglutinins, and their roles in autoimmune reactivities. Alternative Therapies in Health and Medicine [2015, 21 Suppl 1:46-51]. Available here. (2)Nachbar MS, Oppenheim JD. Lectins in the United States diet: a survey of lectins in commonly consumed foods and a review of the literature. Am J Clin Nutr. 1980 Nov;33(11):2338-45. Available here.

Lectins are toxic to humans in large quantities.

Where are lectins found?

Most foods contain insignificant amounts of lectins (e.g. apples, bananas, cucumbers and sweet peppers). The health benefits derived from the vitamins, minerals, fiber and phytochemicals contained in those foods outweigh the negative effects of this small amount of toxins. (3)van Buul VJ, Brouns FJ. Health effects of wheat lectins: A review. Volume 59, Issue 2, March 2014, Pages 112–117. Available here. (4)FDA – U.S. Food and Drug Administration. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Phytohaemagglutinin. Available here.

However, high (but varied) amounts of lectin called phytohaemagglutinin are present in other foods such as legumes (especially red kidney beans, cannellini beans, soybeans and lima beans) and some grains. If the amount of lectins is not reduced, they can have a toxic effect in the human body. This may occur due to the improper preparation of legumes and grains.

The most common source of poisoning from lectins occurs from beans, especially red kidney beans, when they are eaten undercooked or raw. Raw red kidney beans contain between 20,000-70,000 hau (hemagglutinating unit – measure unit of this toxin). Fully cooking these beans reduces the amount of this toxin to only 200-400 hau.

Cannellini beans contain 70% less lectins than red kidney beans and broad beans contain about 90% less.

What happens if you consume a high amount of lectins?

If a large amount of lectins are ingested, for example from as little as 4 or 5 undercooked or uncooked red kidney beans, the following short-lasting symptoms (3-4 hours) may occur: (5)Vojdani A. Lectins, agglutinins, and their roles in autoimmune reactivities. Alternative Therapies in Health and Medicine [2015, 21 Suppl 1:46-51]. Available here. (6)FDA – U.S. Food and Drug Administration. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Phytohaemagglutinin. Available here. (7)Health Canada. Lectins in Dry Legumes. Available here. (8)Miyake K, Tanaka T, McNeil PL. Lectin-Based Food Poisoning: A New Mechanism of Protein Toxicity. PLoS ONE. 2007; 2(8): e687. Available here.

  • Vomiting (may be severe)
  • Nausea (may be extreme)
  • Diarrhea (develops from one to a few hours later)
  • Abdominal pain (but not common)

Hospitalization in these cases is rare.

Frequent consumption of large quantities of lectins, however, may lead to:

  • Increased permeability of the small intestine (9)Ovelgonne JH, Koninkx JF, Pusztai A, Bardocz S, Kok W, Ewen SW, Hendriks HG, van Dijk JE. Decreased levels of heat shock proteins in gut epithelial cells after exposure to plant lectins. Gut 2000;46:680-688 doi:10.1136/gut.46.5.680. Available here. (10)Dalla Pellegrina C, Perbellini O, Scupoli MT, Tomelleri C, Zanetti C, Zoccatelli G, Fusi M, Peruffo A, Rizzi C, Chignola R. Effects of wheat germ agglutinin on human gastrointestinal epithelium: insights from an experimental model of immune/epithelial cell interaction. Toxicol Appl Pharmacol. 2009 Jun 1;237(2):146-53. Available here.
  • Disruption of the immune system, by releasing antigens to attack lectins, and of the tissues to which lectins are attached (11)Cordain L, Toohey L, Smith MJ, Hickey MS. Modulation of immune function by dietary lectins in rheumatoid arthritis. British Journal of Nutrition / Volume 83 / Issue 03 / March 2000, pp 207-217. Available here.
  • Increased risk of autoimmune diseases (12)Hamid R, Masood A. Dietary Lectins as Disease Causing Toxicants. Pakistan Journal of Nutrition 8 (3): 293-303, 2009. Available here.

What do lectins do to your digestive tract?

The intestinal tract lining undergoes some natural “wear and tear”, caused by various stress factors, but it has the ability to repair itself quickly. Lectins attach themselves to the intestinal wall, preventing the lining healing process, thereby causing more stress and damage.

Lectins also agglutinate many red blood cell types and interfere with the transport system of the cell membranes and with the metabolism of the cells. (13)FDA – U.S. Food and Drug Administration. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Phytohaemagglutinin. Available here.

What is the most common reason of poisoning?

The most common reports of poisoning from lectins are (14)FDA – U.S. Food and Drug Administration. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Phytohaemagglutinin. Available here.:

  • Raw, soaked kidney beans, in salads or on their own
  • Red kidney beans that have been cooked using low temperature cooking methods: slow cookers, sous-vide, crock pots and adding beans to casseroles cooked at low heat.

Beans cooked at 80 degrees Celsius, which is common in some of these cooking methods, increase the toxicity potential 5 times higher than eating raw beans.

How can you reduce the amount of lectins in the beans?

Foods with high amounts of lectins, such as beans and grains, must be boiled in order to reduce these toxins to safe amounts.

There are a few methods to reduce lectins in beans: (15)Health Canada. Lectins in Dry Legumes. Available here. (16)Srivastava RP, Vasishtha H. Changes in Protein, Sapogenols and Lectins of Different Types of Chickpeas (Cicer arietinum) during Soaking and Germination. Indian Journal of Agricultural Biochemistry Year : 2014, Volume : 27, Issue : 2. Available here.

  • Soaking (soak beans for at least 5 hours prior to cooking and discard the water used for soaking)
  • Sprouting
  • Fermenting (bacteria reduces the toxins by digesting them)
  • Cooking at high temperatures – cook on high heat for more than 10 minutes

NOTE: the canning processes use adequate heat to reduce the amount of lectins to insignificant amounts, so canned beans are safe to eat.

Conclusion

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Lectins are present in many foods in amounts that cause no harm in healthy people.

Foods with high amounts of lectins, such as legumes or grains, should be prepared correctly to destroy those toxins. The most effective way do this is by cooking them in high temperatures.

Beans should not be cooked using low temperature cooking methods.

References   [ + ]

1. Vojdani A. Lectins, agglutinins, and their roles in autoimmune reactivities. Alternative Therapies in Health and Medicine [2015, 21 Suppl 1:46-51]. Available here.
2. Nachbar MS, Oppenheim JD. Lectins in the United States diet: a survey of lectins in commonly consumed foods and a review of the literature. Am J Clin Nutr. 1980 Nov;33(11):2338-45. Available here.
3. van Buul VJ, Brouns FJ. Health effects of wheat lectins: A review. Volume 59, Issue 2, March 2014, Pages 112–117. Available here.
4. FDA – U.S. Food and Drug Administration. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Phytohaemagglutinin. Available here.
5. Vojdani A. Lectins, agglutinins, and their roles in autoimmune reactivities. Alternative Therapies in Health and Medicine [2015, 21 Suppl 1:46-51]. Available here.
6. FDA – U.S. Food and Drug Administration. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Phytohaemagglutinin. Available here.
7. Health Canada. Lectins in Dry Legumes. Available here.
8. Miyake K, Tanaka T, McNeil PL. Lectin-Based Food Poisoning: A New Mechanism of Protein Toxicity. PLoS ONE. 2007; 2(8): e687. Available here.
9. Ovelgonne JH, Koninkx JF, Pusztai A, Bardocz S, Kok W, Ewen SW, Hendriks HG, van Dijk JE. Decreased levels of heat shock proteins in gut epithelial cells after exposure to plant lectins. Gut 2000;46:680-688 doi:10.1136/gut.46.5.680. Available here.
10. Dalla Pellegrina C, Perbellini O, Scupoli MT, Tomelleri C, Zanetti C, Zoccatelli G, Fusi M, Peruffo A, Rizzi C, Chignola R. Effects of wheat germ agglutinin on human gastrointestinal epithelium: insights from an experimental model of immune/epithelial cell interaction. Toxicol Appl Pharmacol. 2009 Jun 1;237(2):146-53. Available here.
11. Cordain L, Toohey L, Smith MJ, Hickey MS. Modulation of immune function by dietary lectins in rheumatoid arthritis. British Journal of Nutrition / Volume 83 / Issue 03 / March 2000, pp 207-217. Available here.
12. Hamid R, Masood A. Dietary Lectins as Disease Causing Toxicants. Pakistan Journal of Nutrition 8 (3): 293-303, 2009. Available here.
13. FDA – U.S. Food and Drug Administration. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Phytohaemagglutinin. Available here.
14. FDA – U.S. Food and Drug Administration. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Phytohaemagglutinin. Available here.
15. Health Canada. Lectins in Dry Legumes. Available here.
16. Srivastava RP, Vasishtha H. Changes in Protein, Sapogenols and Lectins of Different Types of Chickpeas (Cicer arietinum) during Soaking and Germination. Indian Journal of Agricultural Biochemistry Year : 2014, Volume : 27, Issue : 2. Available here.

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