Sugar, mainly. Oatly adds amylase to their mix which breaks down the oat starch into maltose, a type of sugar. While that is happening naturally during digestive process since our saliva contains amylase, it doesn’t happen in that amount, which means Oatly has significantly more sugar than natural oat milk. Maltose also has a glycemic index of 105, which means that it raises blood sugar level more rapidly than even pure glucose. For reference, cane sugar has a GI of 60, lactose of 46. This means the sugar level of Oatly is effectively higher than Coca-Cola’s.