An observation, I acknowledge a far from scientific one: if I make a loaf of 100% wholemeal loaf with 500gms of wholemeal flour, water and salt and use yeast as a leavening agent it 'fills me up' (stops hunger) less than exactly the same ingredients using a sourdough starter. The sourdough keeps me full for longer*. I've checked a few times now - obviously it's not a controlled experiment, just observation and I'm unwilling to commit to it.

Increased fibre is known to moderate blood sugar released from eating carbs - one of the reasons wholegrains are generally better (along with increased nutrients). In theory the fibre content is identical between loaves. It's roughly the same water in the dough prior to baking. So all that has changed is the starter. It's just a curious observation and it'd be fascinating to do a trial with blood glucose monitoring because it seems counterintuitive - if anything the fibre content should be reduced with a longer fermentation dictated by the sourdough process.

It's homemade 100% wholemeal sourdough with 4 ingredients. Not sure it's be the same without wholemeal or more ingredients.

* I'm willing to accept that could be a placebo effect or maybe some other unobserved confounder. I don't think so though.