Ask a Dietitian

There is some plant bashing going on in books and circulating on the internet accusing legumes and nightshade vegetables of promoting weight gain and causing disease and food sensitivities due to lectins.  These stories are starting to make my clients ask questions like: are you sure I should be eating beans?  And aren’t the nightshade vegetables bad for me?  So, I thought I should help clarify a few things.

What are lectins?  Lectins are proteins found naturally in legumes such as beans, lentils, chickpeas, nightshade vegetables such as tomatoes, potatoes, bell peppers, eggplants and grains such as wheat germ, chia and quinoa.  Lectins have been referred to as anti-nutrients because we are not able to digest them and therefore they can travel through our GI tract unchanged.  They can also reduce our ability to absorb certain nutrients.  In small amounts, lectins have benefits to humans by improving immune function and their involvement in cell growth as well as possible cancer therapy.  However, when consumed in large amounts they cause GI irritation, can reduce absorption of nutrients and can cause severe diarrhea and vomiting.

It is well known that eating raw or dried beans such as raw kidney or black beans will cause severe diarrhea and vomiting due to the lectins.  That is why you need to soak dried beans overnight or for one hour and then boil them for 10min-1 hour respectively.  Soaking and then boiling the beans or canning them will denature the lectins rendering them harmless.  Sprouting beans or cooking them in a slow cooker, which has a low temperature, does not denature all the lectins and therefore may still cause GI issues.  Fermenting soybeans appears to reduce lectin content significantly.

The lectins in wheat and quinoa appear to be denatured with cooking as well.  Eating large amounts of raw chia may cause discomfort and bloating for some people due to the lectins.  People also typically eat cooked eggplant and potatoes which therefore would denature the lectins in those foods.  The lectins in raw tomatoes, peppers and peanuts do not appear to cause any GI symptoms and must be better tolerated than those in legumes.

Where did the Idea Come from?

There is a book called the Plant paradox by Steven Gundry, based on an anti-lectin diet which promises weight loss and thyroid health (as per Kelly Clarkson). Other books such as the Paleo Diet and Bullet Proof also call foods with lectins toxic and say they should be avoided.

However, these foods are full of nutrients and when cooked have virtually no lectins left.  It’s also important to note that clinical trials involving the regular consumption of legumes (100g 5 days a week) have shown a reduction in body weight, blood sugars, LDL cholesterol, blood pressure and waist circumference.   Not weight gain.  Moreover, people who eat legumes also tend to have diets higher in fibre, folate, potassium, phosphorus, magnesium, iron and zinc.  Whole grains have been shown to reduce inflammation in research not increase it.

The bottom line is that lectins are proteins found naturally in some plant foods that are known to improve health in small amounts.  Lectins in undercooked dried beans can cause severe illness and should only be eaten if soaked and boiled or after being canned and wheat germ should be toasted before consumption. Potatoes, quinoa and eggplant are best consumed cooked.