This is quite a claim. Eliminating grains from the diet is not at all dangerous, Where is the scientific evidence or convincing example of this? It does not exist. There is ample anthropological, medical, and historical evidence that our bodies have no biological, nutritional, or physiological requirement for grain foods. None. In fact, there is some legitimate debate as to whether we really need much carbohydrate but even if we do, vegetables and fruits are far superior sources of carbohydrate.
There is absolutely no need to have carbs from grains. There is no specific type of carb or nutrient that we need that is found only in grains. That is just silly. Every nutrient that we need can be more easily obtained and digested from other plant and animal foods.
Eliminating grains isn't at all difficult to achieve physically. It is only difficult psychologically. We live in a culture which attempts to *ingrain" i.e. indoctrinate people into the false idea that it is mandatory to consume grain foods when it is simply is not true. If you can digest them and wish to eat them, that is fine. However, it is absurd to tell people that it is dangerous not to eat them. That just isn't true. There are too many documented cases of health improvements and healthy lifestyles achieved from lowering carbs and/or eliminating grain foods.
Your claim doesn't hold up.
Personally, I have not consumed any grain foods or foods containing grains for 5 years and have severely restricted carbs. My health just gets better and better. My ability to absorb nutrients has actually improved so that I no longer have the mineral defiencies and other problems with digestion that I had previously suffered.