Posted 10/24/2014 3:48 PM (GMT -6)
You need to contact the doctor's office and ask them.
I also have issues with constipation and went on the low fiber and low residue diet, etc, before my first colonoscopy. I was severely constipated, typically going nearly 3 weeks between BMs. For the prep, they told me to stop the red/purple/even blue foods/liquids for just 2 days before the test. I think for most, it's just one day before. But, you really need to talk to your doc about the specifics of what they want YOU to do. You could check with the pharmacist (I realize it's a weekend and you can't get in touch with your doc until Monday probably), they might have some advice for you.
Of course, I assume you've had a colonoscopy before if you have the dx of IBS-C. Any clue what they said last time?
When you talk to the doc Monday, I'd also ask them about what to do if the prep doesn't work well for you. You really don't want to end up doing the special diet and the prep only to be told that it didn't work well enough for them to get a good look. So, I'd find out ahead of time what to do in case you aren't getting cleaned out well the night before.
Good Luck and hope it goes well!