I suggest go with an all vegan diet. No alcohol, no meats, no oil (olive oil, vegetable oil etc...). Fruits and veggies only. Lots of greens. You'll feel better in a few weeks.
Colonoscopy's aren't so bad, I've had a few and they saved my life from cancer. Without the colonoscopy, they would have never found the cancer and I'd be dead by now. Highly recommended for anyone over 50....