Question: Seeking dietary advice, I was directed to Dr Steven Gundry’s The Plant Paradox. He claims to have transformed countless lives, but his list of foods to avoid includes a raft of vegetables, grains, legumes, dairy products and vegetable oils. This seems to fly in the face of many other advisers.
Answer: Steven Gundry’s book recommends a lectin-free diet for health. But despite the claimed benefits, no clear scientific evidence shows that lectin-free diets can cure chronic health conditions or autoimmune diseases. Indeed, Gundry’s diet was labelled a fad by many health authorities, who advised consumers to avoid it. But is there any truth to what Gundry, a former cardiothoracic surgeon-turned-nutritionist, writes about lectins? He recommends avoiding foods high in this plant-based protein that binds to carbohydrates. He claims they disrupt cellular communication and cause inflammation, harming the gut and leading to various health issues and weight gain. However, because they are found in a wide range of food groups – such as beans, legumes, vegetables, dairy products, seeds and nuts – avoiding lectins means severely restricting your food intake.
We know plants use lectins to protect themselves against external pathogens such as fungi and other organisms. And those same features of lectins may cause problems with human digestion if they are eaten in their active state. A prime example is the high concentrations of lectins found in red kidney beans. Eating raw or undercooked beans can cause food poisoning, with symptoms such as nausea, vomiting and diarrhoea. But no such issue occurs if the beans are properly soaked and boiled, thereby inactivating the lectins, before consumption.
Indeed, varying levels of lectins exist within food groups. Those with higher levels tend to be foods that we cook before eating, such as wheat and legumes, thereby inactivating many of the lectins.
From a research perspective, most evidence on lectins and health comes from animal studies, which have shown that they can survive transit through the gut and impair the absorption of essential nutrients such as calcium, iron, phosphorus, and zinc. Hence, their effects have been labelled “anti-nutritional”. They can also bind to cells that line the digestive tract, interfering with the healthy operation of the digestive system and its microflora. Because they can bind to these cells for a long time, they have been theorised to play a role in inflammatory autoimmune conditions such as rheumatoid arthritis and type 1 diabetes.
However, a review published in 2021 in the American Journal of Biomedical Science & Research concluded there are more questions than answers regarding dietary lectins and disease. Most notably, the foods that contain the highest concentrations of lectins are the same foods shown to improve our health, such as vegetables, legumes, fruits and nuts. The Mediterranean diet, for instance, is rich in lectins, with its high intake of plant-derived foods. Yet, those who eat a Mediterranean diet have a lower risk of cardiovascular disease and type-2 diabetes.
That lectin-rich foods are associated with better health highlights an essential point about nutritional science: we cannot consider the health impact of one compound in a food without also considering the matrix of other beneficial compounds in that same food. So, the overall effect of the food, rather than one component, is what ultimately matters. More research is needed to understand which lectins are harmful – as not all appear to be harmful – and what effects occur with a specific dose and duration of intake.
Given the current lack of evidence to support the lectin-free diet, there is little to commend following it. The best advice is to shun diets that recommend avoiding or severely limiting a whole food group or staple food without sound, published scientific evidence to support that recommendation.
