I use a variety of organic grains, including ancient grains (date back thousands of years and have not been genetically modified or hybridized), heirloom grains (meaning they date back hundreds of years and have not been genetically modified or hybridized), and modern wheat (hybridized for higher yield and often higher gluten). Note that hybridized means the plants have been bred for a certain characteristic, versus a GMO grain has been genetically altered. I don’t use GMO grains since I use only organic grains, which are always non-GMO. Each grain type has different characteristics, including differences in flavor, texture, gluten structure, protein content, etc. I often am asked which grain is healthiest or which grain is lowest in gluten, which is a hard question to answer.
Generally, higher protein means higher gluten, but that’s not always true. For example, Einkorn is very high in protein, but its gluten structure is weak which makes it easier to digest and even tolerable for some people with gluten sensitivities. Also, gluten content can vary depending on growing conditions, like rainfall, and the region it is grown in. So it’s hard to say which wheat varieties are “highest” or “lowest” in gluten. With that said, gluten isn’t as much of a concern with sourdough since the long fermentation process breaks down carbohydrates and protein (including gluten proteins). The bacteria in the sourdough starter essentially pre-digest the grains (including the gluten protein) for you which reduces anti-nutrients (far more than yeast fermentation) and helps the bread not spike your blood sugar as much. Often times people with gluten sensitivities can eat traditional, long fermented sourdough products.
In the end, the healthiest option depends on your body and what makes you feel the best. I advocate for experimenting with yourself when it comes to diet since no book or person can tell you what is right for you.
Einkorn
Einkorn is considered the oldest variety of wheat and has a deep, nutty flavor. It has a weak gluten structure, despite its high protein content, which makes it easier to digest.
Khorasan (Kamut)
Khorasan, also known by the brand name Kamut, has a sweet, nutty, buttery flavor. It is known to be easier to digest than modern wheat even though it has a high protein content.
Spelt
Spelt has a strong, nutty, sweet flavor. It is known to be easier to digest than modern wheat due to its weaker gluten structure, even though it has a moderately high protein content.
Emmer
Emmer, also known as farro, has a deep, earthy flavor. It has a moderate protein content, but is known to be lower in gluten.