No, it’s not some sort of horror/science fiction movie. Real studies have shown that the bacteria (aka flora) in our guts have a large impact upon our moods.
This seems to be due to signals relayed to the brain through the hormonal link between the adrenal glands and the hypothalamus and pituitary.
Perhaps part of the key to reducing your stress and anxiety is to eat more fibre to feed the helpful microbes as well as some good, traditionally fermented foods like tub-set yoghurt, sauerkrat and kim chi…. but less of the refined carbohydrates and damaged fats which feed the unhelpful microbes.