Is there a big difference between oat milk and milk? Can I drink to lose weight? There is a big difference between oat milk and milk. Milk is pure milk, and it is nutritious, containing extremely high calcium and protein. However, oat milk and oat milk only say that there are grains in it, and a little milk is blended, so they are mixed, and there is no claim that milk is nutritious. Generally speaking, it is not recommended to drink, not milk, but oatmeal milk.