It’s so personal. I’ve seen the world’s best athletes eat porridge, bananas, bagels, energy bars and stuff like that. Use whatever is going to give you a really good amount of carbohydrate that you can easily digest and sits comfortably. I used to sometimes have a plain bowl of pasta for breakfast, because it’s just a lump of fuel that’s going to give you energy.
What you don’t want to do is just copy what someone else is doing and then bail out to the loo because there’s too much fibre. Porridge might be an issue where it’s fine for others. Make sure you’re comfortable with it and try it in all of your long runs.
Also I think a big mistake people make is they focus on the breakfast, but they haven’t thought about what they had to eat the night before and probably the afternoon before. One of the reasons you might suffer with gut issues could not be the breakfast, but actually because there was too much fibre, perhaps too many vegetables, and too much protein in the meal you had in the afternoon or the evening before.
I would look at more beige, bland carbohydrates that are easy to digest, reducing the amount of protein and just a very light amount of vegetables the afternoon and night before as well. So everything’s very settled. It’s very boring. It’s just fuel.