The "leaky-gut" or porous intestine

The intestinal wall has a complex structure. It is lined by a single layer of rectangular cells called enterocytes. These cells are bound together by proteins called "tight junctions" on their side walls and are impermeable to the passage of substances, unless the enterocytes "authorise" their opening. Thus, most of the substances we absorb pass through these cells to enter our body, rather than between them, allowing better control of what does and does not pass through. These cells also have a 'brush border' at the top (the part that faces the intestinal lumen), which are little hairs called microvilli that allow them to absorb many substances very efficiently. Also, on the surface of the microvilli are certain enzymes that help to finish digesting food, the digestion of which began in the lumen of the stomach or intestine thanks to gastric or pancreatic juices, which are liquids loaded with digestive enzymes that are released when we eat. An example of this is lactose, the sugar contained in dairy products, which is digested at the level of the intestinal microvilli thanks to an enzyme called lactase, and whose deficiency can lead to the famous lactose intolerance. When there is chronic inflammation in the intestinal wall, enterocytes can die or lose their microvilli, and this can lead to malabsorption, poor digestion or even intolerance (for example, lactose intolerance can be genetic if the gene encoding lactase is missing, or it can be acquired through excessive chronic intestinal inflammation). Also, "pores" can open up between cells due to loss or malfunction of tight junctions, so that the impermeability of these junctions is lost. There are also molecules such as gluten gliadin (the non-water-soluble part of gluten) that have the ability to bind directly to the tight junctions and open them. Thus, even in the absence of inflammation, these foods can produce intestinal porosity "per se". Intestinal porosity allows substances that should normally stay in the intestinal lumen and not enter our body, such as toxins or pieces of the wall of some intestinal bacteria called lipopolysaccharides, to pass the intestinal barrier without any control by enterocytes. Thus, these substances directly provoke a local inflammatory reaction or even pass into the bloodstream causing inflammation at a distance. For example, lipopolysaccharides can cross the blood-brain barrier, reach the brain and cause neuroinflammation (inflammation of the central nervous system). This is thought to be one of the mechanisms favouring the onset of neurodevelopmental disorders in children, such as autism for example, or neurodegenerative diseases such as Parkinson's or Alzheimer's in adults.

Lectins

Humans have long been omnivorous animals. Throughout evolution, our digestive system has specialised in digesting and assimilating many green plants, wild fruits (especially berries and nuts) and animal products (meat, eggs and fish), as these foods were what we could mainly gather or hunt. For millions of years our digestive system has had very little contact with cereals or leguminous plants. Although we sometimes found "wild" cereals or legumes that we ate, they were far from being our main source of food. However, with the arrival of the Neolithic revolution, where man learned to cultivate the land and domesticate animals, our eating style changed completely. This was about 8,000 to 10,000 years ago. From that time onwards, the consumption of cereals and cereal flours increased dramatically, and to a lesser extent that of pulses, because they were foods that could be easily preserved. And since then, this has only increased. Our digestive system, despite its adaptability and flexibility, has not been able to adapt to such a drastic change in such a short time (yes, yes, 10 000 years is a very short time in the history of evolution). As a result, over-consumption of these foods has put "stress" on our gut and its guardians, the cells of the immune system. 

     One of the reasons why grains and legumes promote inflammation is the presence of substances called lectins. Lectins are proteins found in many plants. Most cereals except rice, millet, teff and little else contain them. In fact, gluten is one type of lectin, although other non-gluten cereals, such as maize or oats, contain similar lectins. All legumes also contain lectins, as do solanaceous plants such as tomatoes, potatoes and aubergines. Lectins are chemical substances that allow plants to defend themselves against predators, as they do not have claws or teeth like animals, nor can they flee when attacked. On the one hand, they produce a certain toxicity and cause intestinal inflammation, so many animals and insects avoid eating them. On the other hand, lectins allow plants to survive, favouring the expansion of their seeds, as the animal gut often has no mechanism to digest them. Thus, the seed ingested by an animal will pass through its digestive tract and come out intact in the faeces a few hours later, while the animal will probably have moved on. In this way the seed will be "planted" elsewhere, surrounded by the wonderful fertiliser that is faeces. Lectins are therefore a very clever and effective form of plant defence. In small doses, they are not a problem for our organism, as our digestive tract can tolerate them. But the problem comes when we ingest too much. And this is what has been happening more and more. From the invention of agriculture to the present day, the consumption of lectin-laden foods has risen sharply, especially since the mid-20th century. It should not be forgotten that, back in the 1960s-70s, health authorities began to recommend the consumption of cereals, milk, cheese, margarine and potatoes as the basis of our diet. These recommendations were later transformed into the famous "nutritional pyramid", which first appeared in Sweden in 1974 and was later exported to the rest of the world, recommending the percentage of each type of food that we should eat for good health. According to this nutritional pyramid, which varied little from country to country, products such as cereals, bread, rice, pasta and dairy products should be at the base of our diet. Today, these recommendations have been more than contested by many scientists, and it has even been demonstrated that the high consumption of carbohydrates has a harmful effect on health and is linked to many chronic diseases such as diabetes and cardiovascular disease. However, this way of eating has become established in Western societies and most people today still think that healthy eating consists of eating this way. This is not to say that these foods should not be eaten, but they should be eaten in moderation and, preferably, with the knowledge of how to prepare them in order to inactivate some of the effect of their anti-nutrients.

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