Oil in the muffin batter is what makes them moist. According tou003ca href=u0022https://www.bobsredmill.com/blog/baking-101/oil-substitutes-bakingu0022 target=u0022_blanku0022 rel=u0022noreferrer noopeneru0022u003e Bob's Red Millu003c/au003e, oil slows down gluten formation to keep certain baked goods tender and fluffy in texture