Having constipation with IBS is really quite common because of the effect that IBS has on our peristalsis, as mentioned above. Any upset in our natural rhythm of the movement of food is likely to cause a blockage or build-up of food matter within the intestines that thus leads to constipation and an inability to pass food effectively out of the body.
The good news is that changes to your diet can be highly effective for managing and easing constipation caused by IBS.
First, however, it is important to ask what has caused your IBS.