What most people know is that oatmeal is a rich source of fiber, some of which absorbs cholesterol away from your bloodstream. Eat oatmeal regularly, and your bad / "lousy" cholesterol level (LDL) will stay down. Besides the fiber, some of the compounds in oatmeal also help lower your cholesterol. So this is one reason: fiber, which keeps you regular and your arteries healthy. It also helps you lose weight.
Oatmeal also prevents sudden drops or spikes in your blood sugar, reduces high blood pressure, and decreases the risk of breast cancer. More research is done to see if it may prevent other types of cancer as well.
Oatmeal contains plenty of vitamins, minerals, and protein, as well as omega-6 and omega-3 fatty acids. Yes, you may not have realized this, but oats contain not only carbs, but also protein and fats. Some of those fats are omega-6 and omega-3 fatty acids. Yes, the famous omega-3, albeit in a small amount. If you thought only cold-water fish (salmon, tuna, sardines, herring, etc.), nuts (walnuts, butternuts, and to a lesser extent peanuts, cashews, hazelnuts, and other nuts) and certain seeds (flaxseeds, pumpkin seeds, etc.) were a source of omega-3 fatty acids, think again.