In a medium sized bowl or measuring cup, add the sugar to the 1.5 cups of water and stir to dissolve. Then add the yeast and gently stir. Let it sit for 5-10 minutes, it will rise and get foamy.
While the yeast is rising, add the rice flour, arrowroot, flax, xantham gum, salt, oil, vinegar and egg whites to a large food processor with the S-blade attached.
Add the risen yeast to the mixture and process for about 10-20 seconds, until the dough starts to come together. It will be a little more wet and sticky than your average dough.
Spray a standard size loaf pan with cooking spray and pour the dough into the loaf pan.
Cover with a kitchen towel, set aside and let it rise for 1 1/2-2 hours.
When the dough is done rising, preheat the oven to 350 degrees.
Bake for 38-40 minutes, until slightly golden on top.
Let it cool in the loaf pan for 5-10 minutes before removing it.
To finish cooling, carefully invert the pan upside down and let the bread sit in a cooling rack for at least 30 minutes.