The metaphysical connection to chronic digestive problems is related to not "digesting" your feelings. If you are denying how you feel, giving into your fears, or suppressing your feelings then the energies of these emotions get lodged in your solar plexus literally twisting you physically trying to make you to take notice of how you have not been acknowledging your own true feelings. In contrast, someone with a balanced solar plexus accepts themselves, acknowledges their own feelings and ergo is able to truly accept and understand the feelings of others. Because a person with a balanced solar plexus honors their feelings, they are able to clearly understand their own wishes. And with a balanced solar plexus they have the energy to use toward feeding their willpower rather than expending it on maintaining their convoluted Rube Goldberg contraption of feeling.
One way to gauge your own clarity of your solar plexus is to ask yourself how you feel about something. If your answer has multiple conflicting feelings then it is very likely that your solar plexus could use some balancing. Malachite is a really awesome stone for helping to bring out these lodged in feelings.