Sardines may be small, but they are packed with nutrients. The oily fish is a source of protein, omega-3 fatty acids, calcium, vitamin D, vitamin B12 and selenium, which can support heart, brain and bone health. They are also often considered a convenient, budget-friendly seafood option. Experts note that people watching sodium intake, or those with gout or certain kidney concerns, may want to be mindful of how often they eat them.