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.

Make sourdough. Ferment longer.

Background

For those unfamiliar with the glycemic index: Foods with a higher value are more likely to cause spikes in blood sugar. On a scale from 0-100, foods like potatoes with a value of 70 or greater have a high glycemic index, while foods like peas and garlic, with a value of 55 or less, have a low glycemic index. There’s also a “very low” glycemic index categories for foods with a rating of less that 20, which includes lots of green vegetables, mushrooms, meat, and sesame and flax seeds. I’m sure everyone reacts a little differently to these foods, but the ratings serve as a tool to help people guess what they should try to eat more of or less of.

Sourdough

According to Wardee Harmon, non sourdough white bread has a glycemic index of 71, in the “high” category, while sourdough bread has a glycemic index of 53, which puts it in the “low” category. That’s because the bacteria and yeast consume the starches and sugars in the flour, so there’s less starch for us to process. The longer the fermentation, the lower the glycemic index. And when I make sourdough bread, I also use quite a bit of whole wheat flour, nuts, and seeds, which fall in the “low” category, even without being processed with sourdough starter.

I do similar recipes. Some other additives I use to increase fiber/lower GI:

Oat bran; buckwheat; Indian rice grass flour (native American, high fiber, high protein); kaniwa; quinoa flour; teff; spelt; rye; amaranth flour; 9-grain cereal to increase fiber (such as Bob's Red Mill).

I frequently use some rye flour, which also adds much flavor to the loaf.

I agree that sourdough breads with their longer-rising times and higher acid content have lower GI.