Hi shiraT, gluten, casein and fructose can all cause a condition of malabsorption, vital nutrients are not absorbed by the small intestine thus creating a condition of deficiency. 50% of the worlds population is casein intolerant, 30% of Europeans and people of European decent are fructose malabsorbers and about 1 in 130 (some say 1 in 60) are gluten intolerant. Ironically I was taking a sublingual B12 but the first 2 ingredients were fructose and sorbitol, within 48 hours after my last one my depression completely lifted and I have been fine since.