What is the difference between quick-cooking and old-fashioned oats…and can they be used interchangeably? —J.M., Wauwatosa, WisconsinQuick-cooking oats and old-fashioned oats are interchangeable, as long as you consider a the differences between the two. Both have been flattened with large rollers, but quick-cooking oats are cut into smaller pieces first. As a result, quick-cooking oats cook faster, and they offer a more delicate texture to baked goods and desserts. If you want a heartier texture, use old-fashioned oats.