What can I change about this bread recipe to lower its glycemic index?
My mother is the founder of the Glycemic Index Foundation of South Africa (http://www.gifoundation.com/), so let's see how well I've been listening to her!

Stephie is right, legume flours do lower the GI. Beans contain slow release carbohydrates which lowers the GI. Chickpea flour is the best to use here. I find you cannot sub more than 1/4 of the total flour in the recipe as it does have a slight odor - much more when the dough is raw, after cooking it's hardly noticeable. 

As for fibre: Because Psylium Husk is SUPER HIGH in fibre - it's like 80 - 90% fibre - a little does go a long way. Use the powder though, as the rough husks can damage the gluten strands (same for wheat bran here... I wouldn't use more than 1/2 cup of wheat bran per loaf) during proofing. I use about 40ml of psylium husk powder per loaf of bread.

BEST way to lower the GI is also to use a longer fermentation process because it allows the living yeast organisms to break down the gluten into a more digestible form. I got this straight from my mother. Artisan Breads with a long, overnight, fermentation process is LOw GI even when white bread flour is used. Longer fermentation also adds incredible flavour, so why not! Double perks! 

But well done for making your own flour. Unbleached, stone ground flour is ideal.