Lectins:

You may already know some of the most famous reasons why pressure cooking is considered healthy, such as the ability of pressure cooking to help vegetables retain some vitamins. But what you perhaps didn't know is that pressure cooking is also one of the best cooking methods for destroying a class of anti-nutrients called lectins in beans. Now, if you don't happen to own a pressure cooker, not to worry, also boiling will inactivate those lectins and you will just need a bit more time. To get the full scoop, keep reading.

First Some Background: What Paleo Folks Say About Bean Lectins. Paleo enthusiasts often talk about lectins, proteins that occur in a wide range of plants. In the Paleo community, lectins have gotten a bad rap because some (but by no means all) lectins can be extremely toxic when consumed in large enough amounts. Agglutinins, which are found in legumes like beans, are an example of a group of lectins that may be problematic.

To support their argument that beans and other legumes are dangerous, Paleo advocates often refer to an investigation described in the April 1999 issue of the BMJ. The investigation followed an apparent food poisoning that affected a large number of hospital workers after they had eaten a meal containing red kidney beans. The investigators found no pathogenic bacteria in the food, but the beans contained an abnormally high concentration of the lectin phyto-hemagglutinin. (1) However, what Paleo folks sometimes forget to mention is that the red kidney beans that caused the incident hadn't been cooked properly.

In fact, according to a study published in the Journal of Agricultural and Food Chemistry, common edible beans that have been prepared and cooked properly are unlikely to cause lectin-related adverse effects in healthy people (2).

Today, even some Paleo experts, such as the best-selling author Chris Kresser, allow properly cooked beans in their clients' diets. In his book, Your Personal Paleo Code, Kresser argues that it's OK to eat beans and other legumes in moderation provided that you tolerate them well and that they don't replace more nutrient-dense foods, and that they are prepared in a way that makes their nutrients more bioavailable.

The Best Ways to Inactivate Lectins in Beans: Pressure Cooking and Boiling. So, how long should you cook beans and other legumes, and at what temperature, if you want to minimize their lectin content? And are there any differences between cooking methods (e.g. pressure cooking vs boiling)? Let's take a look at some facts:

Neither dry nor moist heating at 70°C (158°F) for several hours had any significant effect on the lectin activity of common legumes, a much higher temperature is needed to inactivate legume lectins (3, 4, 5). According to the U.S. Food and Drug Administration (FDA), consumption of beans cooked in slow cookers, which cook food at low temperatures for several hours, has been associated with foodborne illness outbreaks (6). Soaking beans and other legumes in water and then cooking them in water at or close to 100°C or 212°F (i.e. boiling) appears to be highly effective at inactivating legume lectins. When prepared and cooked this way, the lectin activity in fully hydrated soya beans, kidney beans, fava beans (aka broad beans) and lupin seeds was eliminated already after 10 minutes (and after 1 hour when cooked at 95°C) (4, 5, 8). Note, though, that this study only looked at lectins, and longer cooking times may be required to destroy other anti-nutrients/toxins (i.e. to make these legumes safe for consumption).

Pressure cooking seems to be particularly effective at inactivating lectins. One study found that cooking beans for only 7.5 minutes in a pressure cooker was enough to inactivate their lectin activity. (2, 9, 10) Properly processed beans seem to have little to no residual lectin activity, and in most cases, legume lectins appear to be inactivated before the legumes are considered edible. However, since lectins are more resistant to dry heat treatment, soybean oil and certain foods containing soy flour can have some lectin activity. (2, 9, 11)

Beans, The Takeaway. If you've got a pressure cooker and love beans but are worried about their lectin content, you're in luck, pressure cooking is one of the best ways to inactivate lectins in beans. If you happen to have one of those multi cookers that can be used both as a pressure cooker and a slow cooker, only use the pressure cooking functionality for your bean dishes, slow cookers don't reach temperatures high enough to destroy lectins in beans. And, for all those who don't own a pressure cooker, there's no need to worry: also boiling beans is a good way to get rid of lectins, you will just need a bit more time!

References:

1. Freed, D. (1999). Do dietary lectins cause disease? The evidence is suggestive and raises interesting possibilities for treatment. BMJ, 318(7190): 1023-1024.
2. Lajolo F. and and Genevese M. (2002). Nutritional Significance of Lectins and Enzyme Inhibitors from Legumes, Journal of Agricultural and Food Chemistry, 50(22):6592-8.
3. Pusztai, A (1991). Plant lectins. Cambridge University Press, Cambridge, UK.
4. Grant, G and van Driessche, E. (1993). Legume Lectins. Physiochemical and nutritional properties, Recent Advances in Anti-Nutritional Factors in Legume Seeds. Wageningen Pers.
5. Pusztai, A. and Grant, G. (1998). Assessment of lectin inactivation by heat and digestion. Methods Mol Med., 9:505-14.
6. Bad Bug Book, 2nd edition. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook. Food and Drug Administration.
8. Grant, G et al (1982). The effect of heating on the hemagglutinating activity and nutritional properties of bean Phaseolus vulgaris seeds. Journal of the Science of Food and Agriculture, 33, 1324-1326.
9. Liener, I. (1994). Implications of antinutritional components in soybean foods. Crit. ReV. Food Sci. Nutr., 34, 31-67.
10. Bressani, R. (1993). Grain quality of common beans. Food ReV. Int. 9, 237-297.
11. Deshpande, S. (1992). Food legumes in human nutrition: a persona perspective. Crit. ReV. Food Sci. Nutr., 32, 333-363.

• Fully Cook Your Beans And Your Peas Before Eating Them. Cooking And Digestion Could Destroy Some, But Not All Lectins. For Example, The Lectins In Navy Beans Aren't Fully Destroyed During Digestion.