Grains containing least enzyme-inhibiting substances are rolled oats. For they are hard to maintain raw, 'raw' rolled oats are hardly ever really raw, and generally have had some kind of heat-treatment. Brussel sprouts, beetroot, parsley , celeriac, kale, broccoli and peas contain most of these special carbohydrates. Mangold, rhubarb, spinach, purslane, bamboo shoots and beetroot contain most of these special carbohydrates. Mushrooms easily absorb damaging cadmium and arsenium, and contain alkaloids which inhibit digestion and cause gripes.
Many people have no problem at all eating mushrooms however.
Therefore humans did only start eating plants after having discovered how to use fire to prepare food. Vegetables and grains however are not protected this effectively. Heating does not help. Many toxins, like oxalic acid, glycosides, glycoalkaloids, aflatoxins, sterigmatocystine and quercetine are not destroyed by heat. Heating doesn't help at all, but even originates cancerous N-nitroso compounds.