Doctors may tell you to cut the fat, but not all fats are unhealthy. Omega-3 fatty acids may have far-reaching health benefits. Studies suggest they help lower the risk of heart disease, the nation’s top killer. They may also protect against symptoms of depression, dementia, cancer, and arthritis. Omega-3s are found in salmon, nuts, leafy greens, and more – but the health benefits can differ greatly from one source to another.