Is Crohn's disease and Ulcerous colitis hereditary?

It could be. There's a considerable debate about this. I think people can have a predisposition to getting IBD, but the lifestyle, diet, sleep, the way you eat, fasting, overall health, and how often you workout play a HUGE role in your IBD. As David Sinclair says, "Your lifespan is only 20% genetic. The rest is up to you. Take your epigenome into your own hands." He also refers to this Nature article, https://www.nature.com/articles/s41586-019-1411-0

I definitely think how we live and eat is the biggest factor.