Use vegetable glycerine as the liquid sweetener for a low carb version. If you don't need low carb, use Sucanat or honey for more natural options. If you don't use glycerine, then 1 scoop stevia extract is a good choice or you could alternatively use xylitol or about ? more erythritol.*)
Substitute up to the total amount of the flax meal with the same amount of rice protein for an extra punch of protein. Nutribiotic makes a great brand from non-GMO brown rice. You could also use some of this great grass-fed gelatin to firm up the bars and give more protein.