Lectins - Natural Toxins found in some grains and some vegetables
If you look at life from the point of view of a plant, it doesn't want to be eaten. Therefore it works hard to find poisons which make it bitter or unpalatable or ideally kill whatever it is that is eating it. Most plants achieve this to a certain extent but then animals and particularly insects are equally quick to adapt so we end up with a balance in nature of the two. However there are many plants that humans can't eat, although having said that we eat a greater variety of foods than any other mammal. If we have a perfect digestive system and a perfect detoxification system in the liver then these foods do not represent a problem. However should these natural defences break down then some foods may become poisonous to some people.
Lectins are substances in some grains and vegetables which cause the blood to haemolyse. So for example if I injected somebody intravenously with wheat lectin then they would die very quickly. Some plants produce other proteins for a similar reason and these too can be very toxic - the best noted example is ricin which was placed on the tip of a sharpened umbrella to assassinated the Bulgarian diplomat Marcos as he crossed London Bridge. Interestingly he knew he had been assassinated and survived long enough to tell the casualty officer who took a blood test and confirmed the diagnosis.
We don't have any good tests for lectin sensitivity, it is a case of trial and error but the main lectin containing foods for practical purposes are wheat, potato, tomato and most pulses. So if you get reactions to this group of foods then this could explain the mechanism by which that problem could be caused.
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