Beans are generally considered a ‘healthy’ food, but some nutrition experts would have us think otherwise – because they contain ‘antinutrients’ called lectins. Hatty Willmoth writes.
Beans are having a bit of a moment. TikTok and Instagram are stuffed full of foodies making bean recipes: stews, casseroles, burgers, tacos – even black bean chocolate cake.
As many seek to eat less meat for environmental reasons, beans seem a great option.
They’re a plant-based source of protein with much lower carbon emissions than something like beef, and they’re a whole food too, so no need to worry about ultra-processing.
Plus, they’re wholesome, filling, and super affordable – a winning combo during a cost-of-living crisis.
Beans don’t just contain protein; they’re a good source of fibre, B vitamins, and minerals such as potassium and magnesium.
Yet there’s trouble in legume paradise, as some experts warn that beans are not as healthy as they might first appear. The culprit? Lectins.
Are lectins dangerous?
Lectins are proteins that bind to carbohydrates. They’re a type of antinutrient, which means they can disrupt how well our bodies digest beneficial nutrients.
In particular, lectins are believed to interfere with our absorption of calcium, iron, phosphorous and zinc.
Antinutrients appear in all foods, but in vastly different amounts. They’re present in higher quantities in plants, which make compounds such as lectins and oxalates for all manner of processes, including deterring predators – that’s us – from eating them.
Some go as far as to say that lectins are designed to mess with us – and it’s true that we can’t digest them, so they pass through our bodies intact and can interact with substances inside us.
Eating lots of lectins can be poisonous. As little as five raw red kidney beans, for example, can lead to abdominal pain, nausea, vomiting, diarrhoea – and even death.
That’s because raw red kidney beans contain the lectin phytohemagglutinin in very high quantities, which can cause red blood cells to clump together.
In 2006, a Japanese TV show encouraged its viewers to try eating powdered and toasted (i.e. inadequately cooked) white kidney beans, which are really high in lectins. More than 1000 viewers suffered with acute intestinal symptoms as a result, and approximately 100 of them ended up in hospital.
But most of us don’t go round chowing down on lectin sources when they’re totally raw: crunchy potatoes, plain wheat flour and unprocessed legumes.
No, these are foods that we cook – and cooking is very effective at getting rid of lectins. Boil kidney beans for 10 minutes, for instance, and their lectin content is virtually undetectable – hence why chilli con carne isn’t lethal.
Plus, in the UK, the cans of beans on our supermarket shelves have already been cooked, so their lectin content is really minimal. They may be cold, but they’re not actually raw.
That said, cooked beans and about 30% of the foods we eat still contain a noticeable amount of lectins, so some people maintain that they could be harmful to long-term health.
The Plant Paradox: bye bye, beans!
All the way back in 2017, heart surgeon Dr Steven Gundry wrote a book called The Plant Paradox.
In it, he maintains that lectins can irritate and damage the gut, especially its lining, leading to a condition called increased intestinal permeability (aka. leaky gut syndrome) where compounds such as lectins can pass through the gut wall and into the bloodstream.
Once in the blood, Gundry says, lectins can interfere with tissues all over the body. In turn, this can stimulate a reaction from the immune system in the form of inflammation.
He says this can lead to, or exacerbate, autoimmune conditions such as arthritis, chronic fatigue syndrome and psoriasis, and elevate the risk of metabolic disorders such as obesity and type 2 diabetes.
The Plant Paradox therefore calls on its readers to drastically reduce lectin-rich foods in their diets for the sake of their health, warning of the risk of gut damage, autoimmune diseases, and metabolic dysfunction.
Gundry then proposes a low-lectin diet which involves cutting out beans, other legumes (including lentils, soy and peas), gluten, most dairy, and some vegetables (including aubergine and tomatoes), fruits, nuts (such as peanuts) and seeds.
To bean or not to bean?
Gundry does not want us to eat beans, but his evidence is arguably not compelling enough to warrant throwing away burritos for good.
Research on lectins is limited, so we don’t confidently know what small amounts of lectins actually do to humans.
Most of the studies that warn about lectins’ harmful effects rely on studies carried out in test tubes or on animals, and a 2020 review concluded that evidence from clinical human trials didn’t produce similarly scary results.
It turns out that adding pure lectins to a dish of rabbit blood is not even remotely the same as some guy eating beans on toast for breakfast!
The same review went on to say: “There is currently no strong evidence from human trials to support the claim that lectin-rich foods consistently cause inflammation, intestinal permeability, or nutrient absorption issues in the general population.”
There is some evidence in Gundry’s favour. For instance, one study found that lectins passed through the gut barrier into the bloodstream of a small proportion of people (between 8% and 15% of their 500 participants), and they speculated that this could contribute to autoimmunity.
But that’s not to say that lectins caused either this permeability or havoc once in the blood, and there’s no conclusive evidence to prove the autoimmunity connection.
Some studies have investigated possible mechanisms through which lectins may contribute towards autoimmunity and suggest that certain individuals may be sensitive to lectins, particularly those with pre-existing autoimmune conditions or gut issues.
Again, though, there’s no conclusive evidence either way.
What about the beanefits?
For the general population, though, major scientific reviews suggest that eating a diet that includes legumes is very healthy.
Beans are associated with longer lifespans and a lower risk of cardiovascular disease, obesity and type 2 diabetes.
They’re generally considered to be full of gut-healthy fibre, a good source of slow-release carbohydrates, and anti-inflammatory; some evidence suggests that lectins themselves have anti-inflammatory properties.
Scientists just don’t yet know when the quantity of beans in a diet crosses the threshold from beneficial to harmful, or if that’s how it works at all.
As always, the answer is likely personal. Some may benefit from banning beans; for most of us, they are probably fine.
If you suspect you have a lectin sensitivity, you may wish to try out an elimination diet to see whether beans make your symptoms worse – and if so, a low-lectin diet could be helpful.
If you don’t want to give up beans completely, it may help to boil your beans for longer than usual and reduce your intake of varieties with the highest lectin content, such as red kidney beans.
If you’re still worried, you may wish to see a registered nutritional therapist or speak to a doctor about a potential sensitivity.
Some bean recipes:
If, instead, you feel inspired to get cooking with beans, why not read this article about baked beans, or try out the following recipes?
- Easy sausage and bean stew
- Very chocolatey black bean brownies
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