"Why do I have food intolerances?

Food intolerances are growing and more and more people are unable to eat FODMAPs-containing foods, histamine-containing foods, nightshades, legumes, fructose-containing foods and numerous others, sometimes reduced to consuming only a handful of "safe" foods. Why is this happening, something that was virtually unknown only a generation or two ago? Much of it is due to the excessive proliferation of Proteobacteria species in your gut. But it's not just about food intolerances, as these i...