Inadequate preparation of lectin-containing foods, especially beans, poses a public health risk, said the European Food Safety Authority (EFSA) in a recent opinion report. The information follows reports from several European countries of foodborne illness linked to lectins.

Between 2019 and 2023, Swedish authorities recorded 357 cases of lectin-related illness from insufficiently cooked beans, “often in the form of bean patties.”

Meanwhile, in 2018, French authorities tracked an outbreak of acute gastroenteritis in 200 people to an insufficiently cooked chili con carne at a military base in Brittany, France.

Irish health authorities responded to these outbreaks by issuing precautionary advice on uncooked or raw beans in 2024.

“Lectins are a group of proteins naturally present in many plants, such as legumes, grains, and vegetables. While most are harmless, some lectins, mainly found in raw pulses, can be harmful to humans,” Irene Zanetti, communication officer at EFSA, told Medscape Medical News.

Beans Need Proper Processing

EFSA’s report is the first quantitative risk assessment of plant lectins to have been conducted at the European level. It focuses on lectins found in common edible plants and the impact of food processing, such as soaking and cooking, on lectin activity.

The agency found that phytohemagglutinin (PHA), a principal lectin in beans, affects the small intestine, pancreas, and immune system in animals. Research also suggested that consuming undercooked beans may trigger acute gastrointestinal illness and allergic reactions in humans.

Adequate food processing, such as soaking and boiling beans, deactivates lectins, making food safe to consume, EFSA wrote.

Exactly how long to soak and boil legumes varies between health bodies and countries. While the World Health Organization recommends soaking dried beans for at least 12 hours and then boiling them vigorously for at least 10 minutes in water, the Danish Veterinary and Food Administration recommends 10-12 hours of soaking followed by 30-60 minutes of boiling.

EFSA noted that more data and research are needed to fully understand how plant-based lectins affect health. Limited toxicologic data meant they could investigate only PHA and not other lectins. They also had limited human data, with most evidence coming from animal studies.

Doctors Be Wary

Clinicians need to be aware of proper cooking methods for deactivating lectins so they can inform patients who follow vegetarian and vegan diets, Nicolai Zederkopff Ballin, PhD, chief consultant of food chemistry at Denmark’s Ministry of Food, Agriculture and Fisheries, told Medscape News Europe.

Ballin and colleagues indicated in a 2021 study that there is a need for establishing official threshold levels for active lectins in food.

“There is no reason why lectins should be treated differently compared to all the nonprotein natural toxins that are safely evaluated and regulated in various food laws,” they wrote.

Ballin explained that kidney beans are most often involved in Danish outbreaks due to their popularity and high level of active lectins, necessitating longer boiling times for their deactivation.

Not all legumes require the same cooking time, however. Split red and yellow lentils, for example, do not require soaking and only need to be cooked for 10-15 minutes, Cornelia Witthöft, PhD, professor of food science at Linnaeus University, Växjö, Sweden, told Medscape News Europe.

As a rule of thumb, Witthöft noted that peas and beans often contain higher amounts of lectins and other antinutrients and thus require longer soaking and boiling times. The size and kernel affect cooking time; beans are larger than smaller lentils and thus require more preparation, she explained.

Canned products that have been sufficiently heat-treated are safe, she added, although aquafaba — residue water from cooking — from chickpeas may still contain some lectins.

Those with irritable bowel syndrome should limit intake of pulses, said Witthöft, adding that people with peanut allergies may be more sensitive to lectins from other legumes due to cross-reactivity of antibodies to other proteins. Older people with peanut allergies may be a risk group, she added.

Ballin noted that diarrhea tends to be the main symptom, followed by vomiting, nausea, and stomach pain, with onset ranging between 1 and 8 hours after consumption and averaging around 3.5 hours after consumption.

“Interestingly, most outbreaks originate from canteens, probably due to the difficulty of properly boiling large volumes of beans,” he said.

EFSA recommends that policymakers should consider establishing guidelines or regulations for safely preparing lectin-containing foods and that they promote public awareness of the importance of sound preparation.

Ballin and Witthöft reported having no relevant financial relationships.

Annie Lennon is a medical journalist. Her writing appears on Medscape Medical News, WebMD, and Medical News Today, among other outlets.