Omega-3 is an essential fatty acid that your body cannot make, so you must get it from your diet. It is found naturally in fish oil, which means it can be difficult to get enough of what you eat alone. How to use: Omega-3 is an essential fatty acid that your body cannot produce, so you must obtain it from your diet. It is found naturally in fish oil, which means it can be difficult to get enough of what you eat alone.