Lectins in Beans: Cooking Dried Beans Safely
What lectins in beans are, why raw or undercooked red kidney beans can cause poisoning, what agencies and studies say about soaking and boiling, and why canned beans are safe.
Content last updated . This page has not been medically reviewed.
Beans are healthy, everyday food, and almost all bean problems are avoidable with plain cooking. One real exception is red kidney beans that are raw or not cooked enough. They contain a natural protein called phytohaemagglutinin (PHA), a type of lectin. Lectins are proteins that bind to carbohydrates, and plants make them as a defense. [2] This guide explains what the research and food agencies say, what they disagree on, and what we could not confirm. It is information, not medical advice.
Read this first
- The risk is real but specific. Raw or undercooked red kidney beans are the usual cause of lectin poisoning. Symptoms are nausea, vomiting and diarrhea, usually starting within 1 to 3 hours. [1] [4]
- Four or five raw, soaked dark red kidney beans have been reported to be enough to cause poisoning, according to a 2025 study that also measured the PHA in beans. [4]
- Canned beans are already cooked. The FDA says the low PHA levels in canned and properly cooked kidney beans will not affect you. [1] Harvard's Nutrition Source calls canned beans low in lectins. [2]
- Slow cookers set on low are a known trap when used to cook raw beans, according to Harvard's Nutrition Source. [2]
- Emergency: if someone is very unwell after eating beans, especially a child, get medical help. Call 911 (or your local emergency number) for an emergency. In the US, Poison Help is 1-800-222-1222. See poisoning: what to do first.
What lectins are, and are they bad for you?
Lectins occur in all plants, with the highest amounts in raw legumes and in whole grains such as wheat. [2] Cooking with wet heat, such as boiling, and soaking for several hours can inactivate most lectins, because lectins dissolve in water and sit on the outside of foods. [2]What about long-term harm? Harvard's Nutrition Source (reviewed January 2022) says animal and cell studies suggest lectins might interfere with absorbing calcium, iron, phosphorus and zinc, and that a link to autoimmune disease is theoretical and not established. [2] It also says human research on how much active lectin people eat and what it does long term is very limited, that the anti-lectin diet movement is built largely on theory, and that large population studies link lectin-containing foods such as legumes, whole grains and nuts to lower rates of heart disease and type 2 diabetes. [2] The page concludes that the benefits outweigh the possible harm. [2] Observational studies cannot prove cause, so we say "linked to," not "prevents."
People with irritable bowel syndrome or a sensitive gut may be more likely to have symptoms; the Nutrition Source suggests smaller or less frequent portions of foods that cause trouble. [2] See beans, gas, FODMAPs and digestion.
How dangerous is it, and how often does it happen?
| Source | What it reports |
|---|---|
| UK analysis (1990) | 50 suspected red kidney bean poisoning incidents between 1976 and 1989; nine confirmed by finding the lectin in the beans; many involved beans eaten raw or inadequately heated. [5] |
| French military base (2018) | 200 of 1,700 diners got gastroenteritis (attack rate 12%) after chili con carne made with undercooked raw kidney beans; median onset 3.3 hours. [6] |
| Child case report (2026) | An 8-year-old needed CPR and intensive fluids after a home-cooked red kidney bean dish. She recovered with supportive care. There is no specific antidote. [7] |
| 2025 laboratory study | Measured PHA in raw dark red kidney beans; commercially canned cooked beans had more than 99% less PHA than raw. [4] |
Most cases are short-lived, and the report of a child in shock is a single case that shows what is possible, not how often it happens. [7] We did not find a source with a reliable count of poisonings per year.
Soaking and boiling: what agencies and studies say
The advice differs by source, so we show it side by side. Always follow your own national food-safety authority.| Source | Soak | Boil |
|---|---|---|
| FDA (natural toxins page) | At least 5 hours | At least 30 minutes in fresh water [1] |
| Danish recommendation, as reported in a 2021 lectin study | 10 to 12 hours | 30 to 60 minutes; the study's authors judged this sufficient to inactivate lectin in beans and lentils [3] |
| Harvard Nutrition Source | Several hours | Boiling or stewing; no minute count given. Simmering at low heat, as in a slow cooker, or undercooking may leave lectins [2] |
In the 2021 study, raw kidney beans had about 13,200 hemagglutinating units per gram, and no activity was detected after soaking and boiling. [3] Earlier UK poisoning cases were linked to 3,200 to 102,000 units per gram, and the authors cite 400 to 3,200 as possibly toxic. [3] They also say no official threshold for active lectin exists. [3]
Other food-safety bodies publish a shorter boil time after soaking. We did not read those pages for this guide, so we do not quote them here; our kidney beans page lists what Health Canada and an Australian food-safety council say. If your local authority gives a different time, follow it. [1]
Do not cook raw beans only in a slow cooker. A 2021 study notes slow cookers may not reach temperatures high enough to destroy lectins. [3] Harvard says the same about low-heat simmering. [2]
Canned beans and other beans
- Canned beans: see above. The FDA and Harvard both describe canned beans as safe from this issue. [1] [2] A 2025 study found a whole can of cooked beans (about 94 g of dry matter) would give about 0.46 mg of PHA, roughly 1,000 times below the estimated poisoning dose. [4]
- Other beans have lectins too. The 2021 study found lima beans and black beans had the highest activity among unsoaked beans, with pinto, white, borlotti and kidney beans lower. Green lentils had the highest activity in one test method. [3] After soaking and boiling, activity was fully inactivated in beans. Chickpeas kept some activity. [3] The authors point out that high lectin activity does not necessarily mean the food is toxic to people. [3] Poisoning reports in our sources are almost all about red kidney beans. [4] [5]
- Lima beans also have a separate natural toxin question (cyanide-releasing compounds). We did not read a cooking guideline for it; see the lima beans page.
- Cooking in general: a 2026 review says heat treatment neutralizes heat-sensitive antinutrients but can lower antioxidant capacity, a laboratory finding and not a health result. [8]
What to do if someone gets sick
Call a doctor or poison center and describe what was eaten. Do not wait for a child to improve. The case report notes treatment was supportive, mainly fluids. [7] If anyone has trouble breathing or swelling of the face or throat, that is a different problem, possibly an allergic reaction: call 911.Related pages
Frequently asked questions
Are canned kidney beans safe?
Yes for lectin poisoning, according to the FDA, which says the low PHA levels in canned and properly cooked kidney beans will not affect you. [1] A 2025 study found canned beans had over 99% less PHA than raw. [4]
Can I cook dried kidney beans in a slow cooker?
Harvard says raw beans simmered at low heat, as in a slow cooker, may keep their lectins. [2] The FDA's steps are to soak at least 5 hours and boil in fresh water at least 30 minutes. [1]
Should I avoid lectins?
The Nutrition Source says the anti-lectin movement rests largely on theory, and that foods rich in lectins are linked to lower rates of heart disease and type 2 diabetes in population studies, though that is observational. [2]
Do I need to worry about lentils or chickpeas?
In a 2021 lab study, soaking and boiling removed measurable lectin activity from beans and lentils, but chickpeas kept some. [3] The poisoning reports we read are about red kidney beans. [4] [5]
How fast do symptoms start?
Usually within 1 to 3 hours, according to a 2025 study and a 2026 case report. [4] [7]
References
- U.S. Food and Drug Administration. Natural toxins in food. Read 2026-10-24.
- Harvard T.H. Chan School of Public Health. Lectins (The Nutrition Source). Last reviewed January 2022. Read 2026-10-24.
- Adamcová A, Laursen KH, Ballin NZ. Lectin activity in commonly consumed plant-based foods: calling for method harmonization and risk assessment. Foods 2021;10(11):2796. Read 2026-10-24.
- Thompson HJ, Neil ES, McGinley JN, Lutsiv T. Toward standardized measurement of active phytohemagglutinin in common bean, Phaseolus vulgaris L.. Foods 2025;14(24):4247. Read 2026-10-24.
- Rodhouse JC, Haugh CA, Roberts D, Gilbert RJ. Red kidney bean poisoning in the UK: an analysis of 50 suspected incidents between 1976 and 1989. Epidemiol Infect 1990 (abstract read via Europe PMC). Read 2026-10-24.
- Watier-Grillot S et al. From foodborne disease outbreak (FBDO) to investigation: the plant toxin trap, Brittany, France, 2018. Toxins 2023 (abstract read via Europe PMC). Read 2026-10-24.
- Haile AM et al. Severe red kidney beans toxicity in an 8-year-old girl: a rare case of hypovolemic shock and prerenal acute kidney injury. Int J Emerg Med 2026 (abstract read via Europe PMC). Read 2026-10-24.
- Janahar JJ, Balasubramaniam H, Zhang Y. Nutritional and functional attributes of legumes: a review of processing methods and their impacts. J Food Sci 2026 (abstract read via Europe PMC). Read 2026-10-24.