I follow a pretty intense core/abs workout since 15 days and I have diarrhea since 12-13 days, can it be linked? I mean, does such kind of workout compress so much the bowel that it 'liquify' its 'production'? If so, does it get back to a normal when the core is sufficiently strong? (I have a weak core)
No. Diarrhea is a symptom of what's going on inside your stomach. Your abdominal muscles are outside, and don't have any effect on your digestive system.
If you have a problem with diarrhea, you should take a second look at what you're eating, as a poor diet is the number one cause of diarrhea.
If you're certain that it's not the diet, see a doctor. You could have an infection like gastroenteritis, which is very annoying and also very contagious.
Certain types of exercise cause food to pass through your digestive tract faster than normal. ... It often occurs during or after intense forms of exercise such as running, weightlifting, and cycling. Though it's not convenient, diarrhea connected to working out is relatively normal and usually isn't a cause for concern.