Fermented whole grain or sourdough breads have some benefit in moderation due to either their fiber content and reduction in gluten and specific sugars due to the wild yeast and bacteria content of the fermentation process. These breads have a lower glycemic index than ‘regular’ bread so the impact to your blood sugar is slower compared to the spike you get from highly refined carbohydrate foods. Additionally, these types of breads can support the creation of short-chain-fatty-acids in the colon which are beneficial to your health on multiple levels because they nourish the cells in your GI tract, metabolize carbohydrates and fats, and lower inflammation. If you are going to include bread in your diet, 100% whole grain fermented or sourdough is the best option, but should still be used in moderation in the context of a whole-foods diet. While some people with gluten sensitivity (not an allergy) may be able to consume small amounts of sourdough bread without digestive discomfort due to the reduction in gluten content due to fermentation, if you are one of the many people with a gluten allergy, both should be avoided unless your bread uses 100% gluten-free whole grains.