In order to perceive something subtle there needs to be a degree of peace and quiet in the environment. This is the Weber Fechner law. A flame is bright in a dark cave and imperceptible on a bright sunny day. Our internal signals are clear when our system and habits are more still and imperceptible when we busy ourselves and buzz around with a multitude of inputs. Becoming a skilled noticer and quietening our life enables us to detect important signals. From there we can build and test hypotheses as to what foods and habits affect us in what ways