What can I change about this bread recipe to lower its glycemic index? I'm starting with a recipe from Peter Reinhart's Whole Grain Breads that uses an overnight autolyse of a soaker (whole wheat flour, your choice of other grains, salt, and water) and a refrigerated  biga (whole wheat flour, a small bit of commercial yeast, and water). The recipe is for a hearth bread. I grind my own hard white wheat on the finest grind my KitchenAid mixer attachment can manage.

I'm looking to increase the fiber and protein content. The options I'm looking at in the "other grain" category include 


psyllium husk: I am having a great deal of difficulty finding any instructions on baking with psyllium husk outside of gluten free baking, which I am obviously not doing. I am most concerned with how the psyllium might impact the water content of the recipe and how much is too much, given how small a standard serving is. I don't even know if using psyllium husk is a good idea given that no one seems to have tried it before.
chia seeds: like psyllium, there aren't a lot of resources on using chia in wheat breads. I found one website that said it worked in commercial applications as up to 5% of the bread without changing much. In my recipe that works out to about 1 oz. Does that make sense?
wheat bran: I have so far found one recipe that used a cup of wheat bran to 2 cups of white flour and 1/2 cup of whole grain mix. It seems like I can safely use a good portion of wheat bran, but I'm unsure of exactly how much
vital wheat gluten: I have always seen a suggestion to use about 1 1/2 tsp. of wheat gluten per 1 c. of wheat flour for increased wheat dough elasticity. How high can I push the wheat content before it gets to be too much? My recipe allows for the "other grains" to be up to 33% of the baker's percentage. Could I use the whole thing on bran or would that taste like sandpaper?
flax seed meal: I've seen people online adding 1/4 to 1/3 c. of flax to bread recipes. Does that sound about right?


Am I missing any high fiber or high protein seeds or grains that I should consider (like a bean, perhaps?).
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.