The new health scare you’ve probably never heard of

Nothing could be healthier than a plate of vegetables and wholegrains, right?This has been the bedrock of official dietary advice for decades. These foods are purported to help protect against chronic health problems including obesity, heart disease and cancer.

But emerging as a new source of dietary confusion and fear are a group of proteins called lectins, found in high concentrations in grains, legumes and other plant foods. So, are foods we believe to be healthy actually doing us harm?

That’s certainly the claim of some doctors and self-styled health experts, who say lectins are causing a host of medical problems, from obesity and irritable bowel syndrome to Alzheimer’s and Parkinson’s disease. In his recent book The Plant Paradox, US heart surgeon Dr Steven R Gundry claims lectins are the “number one danger in the Western diet”.

He recommends avoiding or cutting down on foods that contain high concentrations. (He also sells Lectin Shield supplements on his website to neutralise the effect of lectins –around £60 for a month’s supply).

Gwyneth Paltrow’s wellbeing website, Goop, has embraced Dr Gundry’s theories. Web entrepreneur and alternative medicine proponent Dr Joseph Mercola also believes lectins can “wreck your health”. An internet search of the term “lectin-free diet” now throws up more than 2.5 million results. So, can these claims be true? Or is this another pseudoscience diet fad?

What are lectins?

They’re a group of proteins that bind to carbohydrates and are thought to be present in all living cells. They’re found in high concentrations in the husks of grains, foods that are seeds (such as peas, kidney and soy beans, cashews and peanuts), in the seeds of foods such as cucumbers, red peppers and tomatoes, as well as in some dairy products. There are hundreds of kinds of lectins and they all function differently.

To date scientists don’t fully understand how lectins work, or their role in human health. Some lectins are known toxins. Ricin, for example, is found in the seeds of the castor bean plant and ingesting just a few beans can be fatal. Raw kidney beans are also high in a lectin called phytohaemagglutinin, which can cause symptoms that mimic food poisoning. However, other lectins are known to be benign and some might even have antimicrobial and cancer-preventing properties.

Divided opinion

Dr Gundry and his proponents claim that humans can’t fully digest lectins, so when we eat them in large quantities they damage our intestines. This, they say, can cause ‘leaky gut syndrome’ – a condition (not officially recognised by mainstream medicine) in which lectins escape into the bloodstream and enter the joints, nerve junctions, blood vessels and even the brain, causing inflammation and disease.

However, Jon Rhodes, emeritus professor of medicine at the University of Liverpool, has studied lectins and says they’re so abundant and diverse in nature it “makes no sense” to avoid eating them. “It’s like saying proteins are bad for you just because you can find proteins that have toxic effects,” he says. “You can’t generalise. Scientists have only just scratched the surface of trying to understand what dietary lectins may or may not do.”

There are various theories that focus on the idea that some lectins pass through the gut lining into the bloodstream, causing health problems. For example, for some people it’s possible that some lectins irritate their gut, increasing their sensitivity to cereals and breads. Another theory is that lectins may promote the development of rheumatoid arthritis in certain susceptible people.

But much more research is needed to substantiate these claims; the small number of studies carried out so far have been conducted on laboratory animals using isolated lectins, not actual food.

“It’s just a vaguely intriguing hypothesis with no fact behind it,” says Prof Rhodes. So, to sum up – there’s no need to avoid foods with high concentrations of lectins? “Correct,” he says. “In fact, scientific evidence suggests the Mediterranean diet is the best diet for human health. It’s rich in plant-based foods, wholegrains, legumes and nuts – the opposite in fact of a low-lectin diet.”

Nutritional concerns

Nutritionists are concerned that low-lectin diets are, in themselves, unhealthy. Low-lectin advocates suggest swapping wholegrains for white, because grain husks contain high concentrations of lectins. They also recommend peeling fruit and veg, as most of the lectins are in the skin. Some lectin naysayers claim that corn, corn-fed meat, some dairy, peanuts, cashews and unfermented soy products should be cut out completely – and legumes, grains, fruit and veg from the nightshade family (tomatoes, aubergines, potatoes, bell peppers) and squash should only be eaten sparingly.

“Many of the foods listed as lectin sources also contain fibre, vitamins and minerals,” says a spokesperson for the British Nutrition Foundation. “Peeling fruit and vegetables and choosing white grains over wholegrain removes some of the fibre, fruit and veg from the diet – an important nutrient and two food groups that, in the UK, the general population doesn’t eat enough of as it is.”

The bottom line?

Claims that lectins cause a wide range of medical problems are unproven, and avoiding foods rich in these proteins could actually damage your health. There are hundreds of types of lectins performing different functions in nature, but scientists are only just beginning to explore their role in human health. If particular foods cause you discomfort or make you feel unwell, seek medical advice.

True or false?

Scientists have proved that some lectins trigger disease: FALSE

Some lectins are known toxins: TRUE

All lectins are bad for human health: FALSE

Avoiding foods with high concentrations of lectins could damage your health: TRUE

Scientists know very little about the role of lectins in human health: TRUE