Once your yeast is proofed, add in the egg, egg whites, lightly cooled melted butter (you don't want to scramble the eggs or kill the yeast!) and vinegar. Mix with an electric mixer for a couple minutes until light and frothy. Add the flour mixture in two batches, alternating with the sour cream, and mixing until thoroughly incorporated. You want to mix thoroughly and quickly to activate the xanthan gum, though the dough will become thick as the flours absorb the moisture. 
I don’t have dietary issues and do not adhere to a strict paleo diet. I do, however, have a raging sweet tooth that I try to keep in check by eating a low glycemic diet day to day, and limit high glycemic foods to those times when I am deliberately treating myself to “sweets”. This bread is more the texture of “quick bread” (like banana, or zucchini), which was a surprise. Its very tasty and satisfying, almost rich. This bread will be a good delivery system for peanut butter and bananas or soft boiled eggs.
Evolution of the Human Diet: The Known, the Unknown, and the Unknowable by Peter S. Ungar. Diet is key to understanding the ecology and evolution of our distant ancestors and their kin, the early hominins. A study of the range of foods eaten by our progenitors underscores just how unhealthy many of our diets are today. This volume brings together authorities from disparate fields to offer new insights into the diets of our ancestors. Paleontologists, archaeologists, primatologists, nutritionists and other researchers all contribute pieces to the puzzle. The book has four sections: Reconstructed diets based on hominin fossils--tooth size, shape, structure, wear, and chemistry, mandibular biomechanics. Archaeological evidence of subsistence--stone tools and modified bones. Models of early hominin diets based on the diets of living primates--both human and non-human, paleoecology, and energetics. Nutritional analyses and their implications for evolutionary medicine. https://www.youtube.com/watch?v=LssXGFdueFM