Oat vary among oat varieties. Also, oats products are frequently cross-contaminated with other gluten-containing cereals during grain harvesting, transport, storage or processing. Pure oats contain less than 20 parts per million of gluten from wheat, barley, rye, or any of their hybrids. Use of pure oats in a gluten-free diet offers improved nutritional value from the rich content of oat protein, vitamins, minerals, fiber, and lipids, but remains controversial because a small proportion of people with celiac disease react to pure oats. Some cultivars of pure oat could be a safe part of a gluten-free diet, requiring knowledge of the oat
Rye bread "maslin" (or variants of the name) was the bread of the better-off peasants for hundreds of years, in contrast to the white manchet bread eaten by the rich, and the horsebread eaten by the poorer peasants, which was made of cheaper grains including oats, barley and pulses. Wheat-rye breads, particularly light rye (sissel) and American pumpernickel, but also a combination known as "marble rye", are very closely associated with Jewish-American cuisine, particularly the delicatessen. The bulk of the flour is white wheat flour (often a less-refined form known as "first clear"), with a substantial portion of rye mixed in for