Because oatmeal latte uses oatmeal milk, not ordinary latte milk. Oat is a food with low sugar, low fat and high fiber, and its calories are relatively low. In addition, oat milk contains more dietary fiber and protein, which also helps to increase satiety and reduce calorie intake. In addition, sugar will be added in the process of making ordinary latte, which will also increase the calorie intake. In contrast, oatmeal latte contains less sugar, so the calories are relatively low.