Lectins are a very diverse class of sugar-binding protein chemicals that are found in all forms of life—animals, plants, and microorganisms, including humans. Both plants and animals evolved to use these chemicals. Plants evolved them for defense while animals evolved them for cell-to-cell communication. The concern is that animals eat plants and most plant lectins are designed to make them sick or kill them. On the other hand, plants (except for a few, such as the Venus flytrap, Monkeycaps or Sundew), don't eat animals and have no concerns about animal lectins affecting them—except when plants want their seeds germinated by the consistently moist environment in the gastrointestinal tract of animals.
In plants, the main function of lectins is to protect the plant cells against invading fungi, virus and bacteria (microorganisms). Although not studied extensively, it appears that microorganisms also use their own types of lectins to allow them to bind to animal, insect and plant cells in preparation for invasion into the cells. For example, the influenza virus gets into cells by using a lectin called hemagglutinin to bind to the sugar-proteins on the surface of body cells in the throat and gut. Another example is the gut bacteria, Escherichia coli, which is able to adhere to the surface of epithelial cells of the human gastrointestinal tract using their types of lectins.
Plants can also use their types of lectins to stop microorganisms from binding to the surface of the plant cells, and effectively stopping them from infecting the cells.
Plants also use lectins to protect themselves against the insects and animals that attempt to eat them. They do this by disrupting the "cell-to-molecule" and "cell-to-cell" communication within the organisms, which then leads to organ and immune system dysfunction, and can result in illness or death. Plant lectins cause animal cells such as red-blood cells to clump together. They can disrupt immune T-cell function to cause illness and inflammation. Animals and insects need to be careful which plants they eat when they are not feeling healthy.
In animals, the main function of their types of lectins is to allow "cell-to-molecule" and "cell-to-cell" communication, which is somewhat like the action of Velcro, where each binding process promotes very high communication efficiency, but also allows the binding to be undone quite easily to allow for new communication. This type of communication allows the groups of organ and immune cells to maintain high levels of body homoeostasis and high effectiveness at protecting the body against infection and chemical toxicity.
Humans can only eat a few hundred species of plants out of the hundreds of thousands of species living on the planet. Most plants are just too toxic to eat because each plant species uses a great variety of defense chemicals, and among them are the toxic lectin groups.
Humans suffer poor health when they eat plants with lectins that disrupt the "cell-to-molecule" and "cell-to-cell" communication. Plant lectins are anti-nutrients because block nutrient absorption.
Of the plant foods we eat, most of them have to be cooked, baked or boiled. Their temperature has to be raised to a sufficient level to break down the chemical structure of defense toxins and this includes lectins. The plant lectins that cause us illness are the ones that are stable even after normal cooking or baking, because they are still biologically active when we eat them. The toxic lectins in the foods humans eat are called prolamins. Prolamins are plant storage and defense proteins that also assist with seed germination. Gliadin is the best-known and most thoroughly studied example of a toxic lectin—it is a prolamin.
In the cereal grass seeds (grains) such as wheat, barley and rye, the protein component is gluten. This is a complex molecule that consists of gliadin and glutenins. There are at least 50 toxic molecules in gluten that researchers know are targeted byour immune system using antibodies, B-cells, and T-cells. Gluten disrupts immune and cell-to cell-communication—it is cytotoxic. Examples of non-gluten prolamins in the other grains are: hordein in barley, secalin in rye, zein in corn, kafirin in sorghum, orzenin in rice, and avenin in oats.
Humans can eat certain plants with particular prolamine lectins and not suffer any ill effects—only if they can biologically deactivate them by breaking down their structure into their subunits (peptides and amino acids). We can do this either by cooking or through the action of our stomach's digestive enzymes. However, the prolamin lectins in the grain seeds have a chemical structure that is not broken down by normal temperature cooking nor baking, and they are still biologically active when processed into bakery products and eaten as foods. People with coeliac disease know that even if they char a piece of toast until it is black, they will still experience an immune reaction to the still-chemically-intact gluten.
Grain seeds will germinate if they can remain in a high-moisture and constantly warm, but not hot environment for around 24 hours—this is the gastrointestinal tract of animals. When a herbivore (e.g. a goat) eats the stem, leaves and seeds of grain plants they can obtain carbohydrate nutrition from the cellulose. However when a herbivore eats the hard-shelled seeds of grain plants, they pass through the gastrointestinal tract intact. While in the moist environment the seeds germinate and after they are excreted, they sprout in the stool left by the animal. If the environmental conditions are not right for germination of a cereal plant's seeds, they can also use animals to germinate their seeds. In so doing, they have evolved effective defense lectins to protect the seeds against the immune system in the gastrointestinal tract of animals. Lectins such as gluten assist the plant seed by disrupting the host's immune defense efficiency in this process.
The only animals that can naturally utilise the nutrition of hard-shelled grass seeds (grains) are birds with crops that can grind the seeds into flour (all birds have a crop or gizzard, but those species that eat easily digested foods such as soft-bodied insects, soft fruits, or nectar have very small crops that cannot grind down hard-shelled grass seeds). Note: there are some insects with mandibles that can also grind these seeds into flours and get nutrition from them.
In the last 13,800 years, humans have used tools (mortice and pestle) to grind down the hard seed shells of grains into flours. However the temperature of baking cereal flours into breads and biscuits does not denature the naturally toxic lectins. Every person who eats grains experiences low to high grade immune system inflammation and disruption to the function of gut cells. Those who are unfortunate to create an autoimmune disease related to toxic lectins can experience debilitating symptoms and even death.
Even cancer has been linked to eating cereal grains: Dr. Stanislas Tanchou, a physician, and one of Napoleon’s surgeons, gave a lecture to the Paris Medical Society in 1842 at the time when France was a world leader of science and medicine. This was an era of scientific focus to support the political intention for Europeans to conquer and civilize the world to make it safer for Christianity. Against this political culture, Tanchou in his lecture claimed he could predict the exact incidence of cancer in all the major European cities over the next fifty years, and it was mostly dependent on the percentage of grain-derived foods in an individual’s diet.
Tanchou’s recorded predictions proved true—a certain percentage of people in Berlin fell to cancer, a different percentage for Munich, and so on. This set off a major outrage across the civilised world, since the great mission of this European age had been to civilise every inch of the globe, and here was somebody in the centre of civilisation who declared that uncivilised people following a more indigenous hunter-gatherer diet free of grains were free of the scourge of cancer. Cancer is sometimes called a "Disease of Civilisation".