Soon or later in our life we can all be affected by an adverse reaction between the lectins contained in food and our small intestine. These carbo binding protein are ubiquitaries in the vegetal world and are very useful to plants to protect them against attack. The major lectins are:
-peanut agglutinin
-wheat germ agglutinin
-soy lectin
And many others contained primarily in grains, cereals, nuts and legumes
We never had problems with lectins and there are population of the world where this problem is rarely seen, but sometime our digestive system become weak and in some situation and during stress face a thinning of its lining that combined with the bound of certain lectins to its tissues may cause serious adverse reactions such as bloating, constipation, diarrhea, blooding, and allergic reaction as well.
In all these cases the best thing to do would be eliminate all sorts of lectin sources ( soy, milk, wheat, oat, barley, quinoa, beans, nuts and others ) till the side effects disappear. For some it might even go further for life. 
In some searches this had been related to Blood type, origin, but for others it doesn’t have any relation to it. Better would be to have a diet rich on these nutrients unless you have a problem that is symptomatic, but not specific and may affect your articulation, give headache, autoimmune syndromes and digestive tribulations. Some time the only discards of these food give an immediate relieve. This is what the SCD ( specific carbo diet ) or GAPS ( gastro psychotic syndrome ) diet are all about eliminating all complex carbo, privileging monosaccaride diet and permitting these food, here listed:
• Asparagus, spinach, lettuce, broccoli, beets, cauliflower, carrots, celery, artichokes, garlic, onions, zucchini, squash, rhubarb, cucumbers, turnips, watercress.
• Fermented foods: Sauerkraut, kimchi, pickled ginger, fermented cucumbers, coconut yogurt, kombucha, etc. 
• Meats: Fish, chicken, beef, lamb, organ meats, . Best choice are grass-fed and pastured meats from a local farm. Second best is organic. Avoid factory-farmed meats that contain antibiotics and hormones..
• Low glycemic fruits: Apricots, plums, apple, peach, pear, cherries, berries, etc.
• Coconut: Coconut oil, coconut butter, coconut milk, coconut cream.
• Herbal teas
• Olives and olive oil
Also is suggested to avoid coffee that may react as gluten in sensitive people.
The WGA ( lectin of wheat ) is capable of simulating the effect of insulin, some people might be able to disacctivate it before it react with the intestinal linen, but other are more sensitive, and worse could happen if combined with other grains and legumes. Potatoes tomatoes and eggplants may trigger autoimmune syndrome to the articular system with pain felt in fingers and knee.
But why this is happening more and more now and was less evident before. For two simple reasons:
– We should start to eat whole at an early age instead of white form of cereal that at long term to some sensitive people may trigger important adverse reactions
– And then the touch of man that by genetically modifying food had change for ever the relation between our cells and the foods cells ( i.g. corn, soy, wheat and many others )
What shall we do then : if healthy, eat a varied diet especially whole grain and of old derivation like kamut or spel or Capelli senator and many other different cereals and not just wheat
If sick instead, try to start avoiding all sort of lectins to reintroduce them one at the time and not together to better understand what cause the adverse reaction